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Summary of Significant Accounting Policies | 12 Months Ended
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Dec. 31, 2021
Accounting Policies [Abstract] |
Summary of Significant Accounting Policies | Summary of Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements have been prepared in conformity with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and include accounts of the Company and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Stock Split On October 26, 2020, the Company effected a two-for-one stock split of its common stock and redeemable convertible preferred stock. All share and per share information has been retroactively adjusted to reflect the stock split for all periods presented. Initial Public Offering The Company’s registration statement on Form S-1 (the “IPO Registration Statement”) related to its initial public offering (“IPO”) was declared effective on December 9, 2020 and the Company’s Class A common stock began trading on the Nasdaq Global Select Market on December 10, 2020. On December 14, 2020, the Company completed its IPO, in which the Company sold 50.0 million shares of Class A common stock at a price to the public of $68.00 per share. On the same day, the Company sold an additional 5.0 million shares of Class A common stock at a price to the public of $68.00 per share pursuant to the exercise of the underwriters’ option to purchase additional shares. The Company received aggregate net proceeds of $3.7 billion after deducting underwriting discounts and commissions of $79.3 million and offering expenses of $9.8 million. Upon completing the IPO, all outstanding shares of the Company’s redeemable convertible preferred stock, of which 239,623,894 shares were outstanding prior to the IPO, converted into an aggregate of 240,910,588 shares of the Company’s Class B common stock, including 1,286,694 shares of common stock issuable pursuant to the anti-dilution adjustment provisions relating to the Company’s Series C redeemable convertible preferred stock. Upon the Company’s IPO, the Company recognized $2.8 billion of stock-based compensation expense for awards with a liquidity-event performance-based vesting condition satisfied at IPO. Shares were then issued related to the vesting of the restricted stock units ("RSUs") with such performance-based vesting conditions. The Company withheld 24.2 million shares of common stock based on the IPO price of $68.00 per share to satisfy tax withholding and remittance of approximately $1.6 billion. Under the Company’s restated certificate of incorporation, which became effective immediately prior to the completion of the IPO, the Company is authorized to issue 4,736,000,000 shares of common stock, including 2,000,000,000 shares of Class A common stock, 710,000,000 shares of Class B common stock, 2,000,000,000 shares of Class C common stock and 26,000,000 shares of Class H common stock. As a result, following the completion of the IPO, the Company has four classes of authorized common stock: Class A, Class B, Class C, and Class H common stock, of which Class A and Class B had shares outstanding as of December 31, 2020. In November 2020, 9,200,000 shares of Class H common stock were issued to the Company’s wholly-owned Host Endowment Fund subsidiary and held as treasury stock. COVID-19 Pandemic Beginning in 2020, the coronavirus (“COVID-19”) pandemic severely restricted the level of economic activity globally and continues to have an unprecedented effect on the global travel and hospitality industry. The various government measures implemented to contain the COVID-19 pandemic, such as imposing restrictions on travel and business operations, led to unprecedented levels of booking cancellations. The extent and duration of the impact of the COVID-19 pandemic over the longer term remain uncertain and dependent on future developments that cannot be accurately predicted at this time, such as the severity and transmission rate of COVID-19, the introduction and spread of new variants of the virus, including, for example, the Omicron variant which emerged in November of 2021, that may be more easily transmittable and resistant to currently approved vaccines, the continuation of existing or implementation of new government travel restrictions, the extent and effectiveness of containment actions taken, including mobility restrictions, the timing, availability, and effectiveness of vaccines, and the impact of these and other factors on travel behavior in general, and on the Company’s business in particular, which may result in a reduction in bookings and an increase in booking cancellations. Principles of Consolidation The accompanying consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries and variable interest entities (“VIE”) in which the Company is the primary beneficiary in accordance with consolidation accounting guidance. All intercompany transactions have been eliminated in consolidation. The Company determines, at the inception of each arrangement, whether an entity in which it has made an investment or in which it has other variable interest in is considered a VIE. The Company consolidates a VIE when it is deemed to be the primary beneficiary. The primary beneficiary of a VIE is the party that meets both of the following criteria: (i) has the power to direct the activities that most significantly affect the economic performance of the VIE; and (ii) has the obligation to absorb losses or the right to receive benefits that in either case could potentially be significant to the VIE. Periodically, the Company determines whether any changes in its interest or relationship with the entity impact the determination of whether the entity is still a VIE and, if so, whether the Company is the primary beneficiary. If the Company is not deemed to be the primary beneficiary in a VIE, the Company accounts for the investment or other variable interest in a VIE in accordance with applicable U.S. GAAP. As of December 31, 2020 and 2021, the Company’s consolidated VIEs were not material to the consolidated financial statements. Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company regularly evaluates its estimates, including those related to bad debt reserves, fair value of investments, useful lives of long-lived assets and intangible assets, valuation of acquired goodwill and intangible assets from acquisitions, contingent liabilities, insurance reserves, revenue recognition, valuation of common stock, stock-based compensation, and income and non-income taxes, among others. Actual results could differ materially from these estimates. Segment Information Operating segments are defined as components of an entity for which discrete financial information is available and is regularly reviewed by the Chief Operating Decision Maker (“CODM”) in making decisions regarding resource allocation and performance assessment. The Company’s CODM is its Chief Executive Officer. The Company has determined it has one operating and reportable segment as the CODM reviews financial information presented on a consolidated basis for purposes of allocating resources and evaluating financial performance. Cash, Cash Equivalents, and Restricted Cash Cash and cash equivalents are held in checking and interest-bearing accounts and consist of cash and highly-liquid securities with an original maturity of 90 days or less. The following table reconciles cash, cash equivalents, and restricted cash reported on the Company’s consolidated balance sheets to the total amount presented in the consolidated statements of cash flows (in thousands):
| As of December 31,
| 2019 | 2020 | 2021
Cash and cash equivalents | $ | 2,013,547 |  | $ | 5,480,557 |  | $ | 6,067,438 |
Cash and cash equivalents included in funds receivable and amounts held on behalf of customers | 3,129,781 |  | 2,153,849 |  | 3,645,087 |
Restricted cash | 115 |  | 33,846 |  | 14,764 |
Total cash, cash equivalents, and restricted cash presented in the consolidated statements of cash flows | $ | 5,143,443 |  | $ | 7,668,252 |  | $ | 9,727,289 |
Marketable Securities The Company considers all highly-liquid investments with original maturities of greater than 90 days to be marketable securities. The Company determines the appropriate classification of its investments in marketable securities at the time of purchase. As the Company views these securities as available to support current operations, it accounts for these debt securities as available-for-sale and classifies them as short-term assets on its consolidated balance sheets. The Company determines realized gains or losses on the sale of equity and debt securities on a specific identification method. Unrealized gains and non-credit related losses on available-for-sale debt securities are reported as a component of accumulated other comprehensive income (loss) in stockholders’ equity (deficit). Realized gains and losses and impairments are reported within other income (expense), net in the consolidated statements of operations. The assessment for impairment takes into account the severity and duration of the decline in value, adverse changes in the market or industry of the investee, the Company’s intent to sell the security and whether it is more likely than not that it will be required to sell the security before recovery of the amortized cost basis. The Company’s marketable equity securities with readily determinable fair values are measured at fair value on a recurring basis with changes in fair value recognized within other income (expense), net in the consolidated statements of operations. The Company records an impairment of its available-for-sale debt securities if the amortized cost basis exceeds its fair value and if the Company has the intention to sell the security or if it is more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis. If the Company does not have the intention to sell the security and it is not more likely than not that the Company will be required to sell the security before recovery of the amortized cost basis and the Company determines that the unrealized loss is entirely or partially due to credit-related factors, the credit loss is measured and recognized as an allowance on the consolidated balance sheets with a corresponding charge in the consolidated statements of operations. The allowance is measured as the amount by which the debt security’s amortized cost basis exceeds the Company’s best estimate of the present value of cash flows expected to be collected. Any remaining decline in fair value that is non-credit related is recognized in other comprehensive income (loss). Improvements in expected cash flows due to improvements in credit are recognized through reversal of the credit loss and corresponding reduction in the allowance for credit loss. Non-Marketable Investments Non-marketable investments consist of debt and equity investments in privately-held companies, which are classified as other assets, noncurrent on the consolidated balance sheets. The Company classifies its non-marketable investments that meet the definition of a debt security as available-for-sale. The accounting policy for debt securities classified as available-for-sale is described above. The Company’s non-marketable equity investments are accounted for using either the equity method of accounting or as equity investments without readily determinable fair values under the measurement alternative. The Company uses the equity method if it has the ability to exercise significant influence, but not control, over the operating and financial policies of the investee. For investments accounted for using the equity method, the Company’s proportionate share of its equity interest in the net income (loss) and other comprehensive income (loss) of these companies is recorded in the consolidated statements of operations within other income (expense), net. The carrying amount of the investment in equity interests is adjusted to reflect the Company’s interest in the investee’s net income or loss and any impairments and is classified in other assets, noncurrent on the consolidated balance sheets. Equity investments for which the Company is not able to exercise significant influence over the investee and for which fair value is not readily determinable are accounted for using the measurement alternative. Such investments are carried at cost, less any impairments, and are adjusted for subsequent observable price changes obtained from orderly transactions for identical or similar investments issued by the same investee. This election is reassessed each reporting period to determine whether non-marketable equity securities have a readily determinable fair value, in which case they would no longer be eligible for this election. Changes in the basis of the equity investment are recognized in other income (expense), net in the consolidated statements of operations. The Company reviews its non-marketable debt and equity investments for impairment at the end of each reporting period or whenever events or circumstances indicate that the carrying value may not be fully recoverable. Impairment indicators might include negative changes in industry and market conditions, financial performance, business prospects, and other relevant events and factors. Upon determining that an impairment exists, the Company recognizes as an impairment in other income (expense), net in the consolidated statements of operations the amount by which the carrying value exceeds the fair value of the investment. Fair Value of Financial Instruments The Company applies fair value accounting for all financial assets and liabilities that are recognized or disclosed at fair value in the financial statements. The authoritative guidance on fair value measurements establishes a hierarchical disclosure framework which prioritizes and ranks the level of market price observability used in measuring financial instruments at fair value. This hierarchy requires the Company to use observable market data when available and to minimize the use of unobservable inputs when determining fair value. Financial instruments with readily available quoted prices in active markets generally will have a higher degree of market price observability and a lesser degree of judgment used in measuring fair value. Financial instruments measured and disclosed at fair value are classified and disclosed based on the observability of inputs used in the determination of fair value as follows: Level 1: Observable inputs such as quoted prices in active markets. Level 2: Observable inputs other than Level 1 prices, such as quoted prices in less active markets or model-derived valuations that are observable either directly or indirectly. Level 3: Unobservable inputs in which there is little or no market data that are significant to the fair value of the assets or liabilities. The carrying amount of the Company’s financial instruments, including cash equivalents, funds receivable and amounts held on behalf of customers, accounts payable, accrued liabilities, funds payable and amounts payable to customers, and unearned fees approximate their respective fair values because of their short maturities. Level 2 Valuation Techniques Financial instruments classified as Level 2 within the Company’s fair value hierarchy are valued on the basis of prices from an orderly transaction between market participants provided by reputable dealers or pricing services. Prices of these securities are obtained through independent, third-party pricing services and include market quotations that may include both observable and unobservable inputs. In determining the value of a particular investment, pricing services may use certain information with respect to transactions in such investments, quotations from dealers, pricing matrices and market transactions in comparable investments and various relationships between investments. The Company’s foreign exchange derivative instruments are valued using pricing models that take into account the contract terms, as well as multiple inputs where applicable, such as interest rate yield curves and currency rates. Level 3 Valuation Techniques Financial instruments classified as Level 3 within the Company’s fair value hierarchy consist primarily of a derivative warrant liability relating to the warrants issued in conjunction with the second lien loan discussed in Note 10, Debt. Valuation techniques for the derivative warrant liability include the Black-Scholes option-pricing model with key assumptions such as stock price volatility, expected term, and risk-free interest rates. Internal-Use Software The Company capitalizes certain costs in connection with obtaining or developing software for internal use. Amortization of such costs begins when the project is substantially complete and ready for its intended use. Capitalized software development costs are classified as property and equipment, net on the consolidated balance sheets and are amortized using the straight-line method over the estimated useful life of the applicable software. Property and Equipment Property and equipment are stated at cost, less accumulated depreciation and amortization. Depreciation and amortization on property and equipment is calculated using the straight-line method over the estimated useful lives indicated below:
Asset Category | Period
Computer equipment | 5 years
Computer software and capitalized internal-use software | 1.5 to 3 years
Office furniture and equipment | 5 years
Buildings | 25 to 40 years
Leasehold improvements | Lesser of estimated useful life or remaining lease term
Costs of maintenance and repairs that do not improve or extend the useful lives of assets are expensed as incurred. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statements of operations. Business Combinations The Company accounts for business combinations using the acquisition method of accounting, under which assets acquired and liabilities assumed are recorded at their respective fair values at the date of acquisition, with the exception of contract assets and liabilities which are accounted for in accordance with Topic 606. The excess purchase price over the fair values of these identifiable assets and liabilities is recorded as goodwill. Transaction costs associated with business combinations are expensed as incurred. Leases The Company determines whether an arrangement is or contains a lease at inception. Operating lease right-of-use (“ROU”) assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. Operating lease liabilities represent the present value of lease payments not yet paid. Operating lease ROU assets represent the Company’s right to use an underlying asset and are based upon the operating lease liabilities adjusted for prepayments or accrued lease payments, initial direct costs, lease incentives, and impairment of operating lease assets. As most of the Company’s leases do not provide an implicit rate, the Company uses its incremental borrowing rate based on the information available at commencement date in determining the present value of lease payments. The Company has real estate and equipment lease agreements that contain lease and non-lease components, which are accounted for as a single lease component. The Company’s leases often contain rent escalations over the lease term. The Company recognizes expense for these leases on a straight-line basis over the lease term. Additionally, tenant incentives, primarily used to fund leasehold improvements, are recognized when earned and reduce the Company’s right-of-use asset related to the lease. These are amortized through the right-of-use asset as reductions of expense over the lease term. The Company’s lease agreements may contain variable costs such as common area maintenance, operating expenses or other costs. Variable lease costs are expensed as incurred on the consolidated statements of operations. The Company’s lease agreements generally do not contain any residual value guarantees or restrictive covenants. For substantially all leases with an initial non-cancelable lease term of less than one year and no option to purchase, the Company elected not to recognize the lease on its Consolidated Balance Sheets and instead recognize rent payments on a straight-line basis over the lease term within operating expense on its Consolidated Statements of Operations. The Company adopted ASU No. 2016-02, Leases (Topic 842) on January 1, 2019. Upon adoption, the Company recognized an operating lease ROU asset of $340.2 million and lease liabilities of $366.0 million, as well as a cumulative-effect adjustment to the opening balance of accumulated deficit of $22.2 million. Goodwill Goodwill represents the excess of the purchase price over the fair value of net assets acquired in a business combination. The Company has one reporting unit. The Company tests goodwill for impairment at least annually, in the fourth quarter, or whenever events or changes in circumstances indicate that goodwill might be impaired. There were no impairment charges in any of the periods presented in the consolidated financial statements. Refer to Note 6, Intangible Assets and Goodwill, for additional information. Intangible Assets Intangible assets are amortized on a straight-line basis over the estimated useful lives ranging from one to ten years. The Company reviews intangible assets for impairment under the long-lived asset model described below. There were no impairment charges in any of the periods presented in the consolidated financial statements. Refer to Note 6, Intangible Assets and Goodwill, for additional information. Impairment of Long-Lived Assets Long-lived assets that are held and used by the Company are reviewed for impairment when events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable. Determination of recoverability of long-lived assets is based on an estimate of the undiscounted cash flows resulting from the use of the asset and its eventual disposition. If the carrying value of the long-lived asset is not recoverable on an undiscounted cash flow basis, impairment is recognized to the extent that the carrying value exceeds its fair value. Fair value is determined through various valuation techniques including discounted cash flow models, quoted market values, and third-party independent appraisals, as necessary. Any impairments to ROU assets, leasehold improvements, or other assets as a result of a sublease, abandonment, or other similar factor are initially recognized when a decision to do so is made and recorded as an operating expense. Similar to other long-lived assets, management tests ROU assets for impairment whenever events or changes in circumstances occur that could impact the recoverability of these assets. For ROU assets, such circumstances may include subleases that do not fully recover the costs of the associated leases or a decision to abandon the use of all or part of an asset. For the years ended December 31, 2020 and 2021, the Company recorded $35.8 million and $112.5 million, respectively, of long-lived asset impairment charges within restructuring charges in the consolidated statement of operations. The Company had no impairments of long-lived assets for the year ended December 31, 2019. Revenue Recognition The Company generates substantially all of its revenue from facilitating guest stays at accommodations offered by Hosts on the Company’s platform. The Company considers both Hosts and guests to be its customers. The customers agree to the Company’s Terms of Service (“ToS”) to use the Company’s platform. Upon confirmation of a booking made by a guest, the Host agrees to provide the use of the property. At such time, the Host and guest also agree upon the applicable booking value as well as Host fees and guest fees (collectively “service fees”). The Company charges service fees in exchange for certain activities, including the use of the Company’s platform, customer support, and payment processing activities. These activities are not distinct from each other and are not separate performance obligations. As a result, the Company’s single performance obligation is to facilitate a stay, which occurs upon the completion of a check-in event (a “check-in”). The Company recognizes revenue upon check-in as its performance obligation is satisfied upon check-in and the Company has the right to receive payment for the fulfillment of the performance obligation. The Company charges service fees to its customers as a percentage of the value of the booking, excluding taxes. The Company collects both the booking value from the guest on behalf of the Host and the applicable guest fees owed to the Company using the guest’s pre-authorized payment method. After check-in, the Company disburses the booking value to the Host, less the fees due from the Host to the Company. The Company’s ToS stipulates that a Host may cancel a confirmed booking at any time up to check-in. Therefore, the Company determined that for accounting purposes, each booking is a separate contract with the Host and guest, and the contracts are not enforceable until check-in. Since an enforceable contract for accounting purposes is not established until check-in, there were no partially satisfied or unsatisfied performance obligations as of December 31, 2020 and 2021. The service fees collected from customers prior to check-in are recorded as unearned fees. Unearned fees are not considered contract balances because they are subject to refund in the event of a cancellation. Guest stays of at least 28 nights are considered long-term stays. The Company charges service fees to facilitate long-term stays on a monthly basis. Such stays are generally cancelable with a 30 days advance notice for no significant penalty. Accordingly, long-term stays are treated as month-to-month contracts; each month is a separate contract with the Host and guest, and the contracts are not enforceable until check-in for the initial month as well as subsequent monthly extensions. The Company’s performance obligation for long-term stays is the same as that for short-term stays. The Company recognizes revenue for the first month upon check-in, similar to short-term stays, and recognizes revenue for any subsequent months upon each month’s anniversary from initial check-in date. The Company evaluates the presentation of revenue on a gross versus net basis based on whether or not it is the principal (gross) or the agent (net) in the transaction. As part of the evaluation, the Company considers whether it controls the right to use the property before control is transferred. Indicators of control that the Company considers include whether the Company is primarily responsible for fulfilling the promise associated with the rental of the property, whether it has inventory risk associated with the property, and whether it has discretion in establishing the prices for the property. The Company determined that it does not control the right to use the properties either before or after completion of its service. Accordingly, the Company has concluded that it is acting in an agent capacity and revenue is presented net reflecting the service fees received from Hosts and guests to facilitate a stay. The Company has elected to recognize the incremental costs of obtaining a contract, including the costs of certain referrer fees, as an expense when incurred as the amortization period of the asset that the Company otherwise would have recognized is one year or less. The Company has no significant financing components in its contracts with customers. The Company has elected to exclude from revenue, taxes assessed by a governmental authority that are both imposed on and are concurrent with specific revenue producing transactions. Accordingly, such amounts are not included as a component of revenue or cost of revenue. Payments to Customers The Company makes payments to customers as part of its referral programs and marketing promotions, collectively referred to as the Company’s incentive programs, and refund activities. The payments are generally in the form of coupon credits to be applied toward future bookings or as cash refunds. Incentive Programs The Company encourages the use of its platform and attracts new customers through its incentive programs. Under the Company’s referral program, the referring party (the “referrer”) earns a coupon when the new guest or Host (the “referee”) completes their first stay on the Company’s platform. Incentives earned by customers for referring new customers are paid in exchange for a distinct service and are accounted for as customer acquisition costs. The Company records the incentive as a liability at the time the incentive is earned by the referrer with the corresponding charge recorded to sales and marketing expense in the same way the Company accounts for other marketing services from third-party vendors. Any amounts paid in excess of the fair value of the referral service received are recorded as a reduction of revenue. Fair value of the service is established using amounts paid to vendors for similar services. Customer referral coupon credits generally expire within one year from issuance and the Company estimates the redemption rates using its historical experience. As of December 31, 2020 and 2021, the referral coupon liability was not material. Through marketing promotions, the Company issues customer coupon credits to encourage the use of its platform. After a customer redeems such incentives, the Company records a reduction to revenue at the date it records the corresponding revenue transaction, as the Company does not receive a distinct good or service in exchange for the customer incentive payment. Refunds In certain instances, the Company issues refunds to customers as part of its customer support activities in the form of cash or credits to be applied toward a future booking. There is no legal obligation to issue such refunds to Hosts or guests on behalf of its customers. The Company accounts for refunds, net of any recoveries, as variable consideration, which results in a reduction to revenue. The Company reduces the transaction price by the estimated amount of the payments by applying the most likely outcome method based on known facts and circumstances and historical experience. The estimate for variable consideration was not material as of December 31, 2020 and 2021. The Company evaluates whether the cumulative amount of payments made to customers that are not in exchange for a distinct good or service received from customers exceeds the cumulative revenue earned since inception of the customer relationships. Any cumulative payments in excess of cumulative revenue are presented within operations and support or sales and marketing on the consolidated statements of operations based on the nature of the payments made to customers. The following table summarizes total payments made to customers (in thousands):
| Year Ended December 31,
| 2019 | 2020 | 2021
Reductions to revenue | $ | 274,461 |  | $ | 384,181 |  | $ | 156,160 |
Charges to operations and support | 103,364 |  | 83,093 |  | 68,850 |
Charges to sales and marketing expense | 129,623 |  | 56,680 |  | 46,730 |
Total payments made to customers | $ | 507,448 |  | $ | 523,954 |  | $ | 271,740 |
Funds Receivable and Funds Payable Funds receivable and amounts held on behalf of customers represent cash received or in-transit from guests via third-party credit card processors and other payment methods, which the Company remits for payment to the Hosts following check-in. This cash and related receivable represent the total amount due to Hosts, and as such, a liability for the same amount is recorded to funds payable and amounts payable to customers. The Company records guest payments, net of service fees, as funds receivable and amounts held on behalf of customers with a corresponding amount in funds payable and amounts payable to customers when cash is received in advance of check-in. Host and guest fees are recorded as cash with a corresponding amount in unearned fees. For certain bookings, a guest may opt to pay a percentage of the total amount due when the booking is confirmed, with the remaining balance due prior to the stay occurring (the “Pay Less Upfront Program”). Under the Pay Less Upfront Program, when the Company receives the first installment payment from the guest upon confirmation of the booking, the Company records the first installment payment as funds receivable and amounts held on behalf of customers with a corresponding amount in funds payable and amounts payable to customers, net of the Host and guest fees. The full value of the service fees is recorded as cash and cash equivalents and unearned fees upon receipt of the first installment payment to represent what the Company expects to be recognized as revenue if the underlying booking is not canceled. Upon receipt of the second installment, such payment amounts are also recorded as funds receivable and amounts held on behalf of customers with a corresponding amount in funds payable and amounts payable to customers. Following check-in, the Company remits funds due to Hosts and recognizes unearned fees as revenue as its performance obligation is satisfied. Bad Debt The Company generally collects funds related to bookings from guests on behalf of Hosts prior to check-in. However, in limited circumstances the Company disburses funds to a Host or a guest on behalf of a counterparty guest or Host prior to collecting such amounts from the counterparty. Such uncollected balances generally arise from the timing of payments and collections related to a dispute resolution between the guest and Host or certain alterations to stays and are included in prepaids and other current assets on the consolidated balance sheets. The Company records a customer receivable allowance for credit losses for funds that may never be collected. The Company estimated its exposure to balances deemed to be uncollectible based on factors including known facts and circumstances, historical experience, reasonable and supportable forecasts of economic conditions, and the age of the uncollected balances. The Company writes off the asset when it is determined to be uncollectible. Bad debt expense was $77.1 million, $107.7 million, and $27.3 million for the years ended December 31, 2019, 2020, and 2021, respectively. Cost of Revenue Cost of revenue primarily consists of payment processing charges, including merchant fees and chargebacks, costs associated with third-party data centers used to host the Company’s platform, and amortization of internally developed software and acquired technology. Operations and Support Operations and support costs primarily consist of personnel-related expenses and third-party service provider fees associated with customer support provided via phone, email, and chat to Hosts and guests, customer relations costs, which include refunds and credits related to customer satisfaction and expenses associated with the Company’s Host protection programs, and allocated costs for facilities and information technology. These costs are expensed as incurred. Product Development Product development costs primarily consist of personnel-related expenses and third-party service provider fees incurred in connection with the development of the Company’s platform and new products as well as the improvement of existing products, and allocated costs for facilities and information technology. These costs are expensed as incurred. Sales and Marketing Sales and marketing costs primarily consist of performance and brand marketing, personnel-related expenses, including those related to field operations, portions of referral incentives and coupons, policy and communications, and allocated costs for facilities and information technology. These costs are expensed as incurred. Advertising expenses were $712.6 million, $176.0 million, and $542.1 million for the years ended December 31, 2019, 2020, and 2021, respectively. General and Administrative General and administrative costs primarily consist of personnel-related expenses for executive management and administrative functions, including finance and accounting, legal, and human resources, as well as general corporate and director and officer insurance. General and administrative costs also include certain professional services fees, allocated costs for facilities and information technology expenses, indirect taxes including lodging taxes where the Company may be held jointly liable with Hosts for collecting and remitting such taxes, and bad debt expense. These costs are expensed as incurred. Restructuring Charges Costs and liabilities associated with management-approved restructuring activities are recognized when they are incurred. One-time employee termination costs are recognized at the time of communication to employees, unless future service is required, in which case the costs are recognized ratably over the future service period. Ongoing employee termination benefits are recognized as a liability when it is probable that a liability exists and the amount is reasonably estimable. Restructuring charges are recognized as an operating expense within the consolidated statements of operations and related liabilities are recorded within accrued expenses and other liabilities on the consolidated balance sheets. The Company periodically evaluates and, if necessary, adjusts its estimates based on currently available information. Income Taxes Income taxes are accounted for under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax law in effect for the years in which the temporary differences are expected to be recovered or settled. The effect of a change in tax rates on deferred tax assets and liabilities is recognized in the period that includes the enactment date. A valuation allowance is recorded for deferred tax assets if it is more likely than not that some portion or all of the deferred tax assets will not be realized. The Company evaluates and accounts for uncertain tax positions using a two-step approach. Recognition, step one, occurs when the Company concludes that a tax position, based solely on its technical merits, is more-likely-than-not to be sustained upon examination. Measurement, step two, determines the largest amount of benefit that is greater than 50% likely to be realized upon ultimate settlement with a taxing authority that has full knowledge of all relevant information. Derecognition of a tax position that was previously recognized would occur when the Company subsequently determines that a tax position no longer meets the more-likely-than-not threshold of being sustained. Foreign Currency The Company’s reporting currency is the U.S. dollar. The Company determines the functional currency for each of its foreign subsidiaries by reviewing their operations and currencies used in their primary economic environments. Assets and liabilities for foreign subsidiaries with functional currency other than U.S. dollar are translated into U.S. dollars at the rate of exchange existing at the balance sheet date. Statements of operations amounts are translated at average exchange rates for the period. Translation gains and losses are recorded in accumulated other comprehensive income (loss) as a component of stockholders’ equity (deficit). No material amounts were reclassified from accumulated other comprehensive income (loss) for the years ended December 31, 2019, 2020, and 2021. Remeasurement gains and losses are included in other income (expense), net in the consolidated statements of operations. Monetary assets and liabilities are remeasured at the exchange rate on the balance sheet date and nonmonetary assets and liabilities are measured at historical exchange rates. As of December 31, 2020, the Company had a cumulative translation loss of $3.1 million and as of December 31, 2021, the Company had a cumulative translation gain of $2.8 million. Total net realized and unrealized gains (losses) on foreign currency transactions and balances totaled $(4.8) million, $31.5 million, and $(5.1) million for the years ended December 31, 2019, 2020, and 2021, respectively. Derivative Instruments The Company enters into financial derivative instruments, consisting of foreign currency contracts to mitigate its exposure to the impact of movements in currency exchange rates on its transactional balances denominated in currencies other than the functional currency. The Company does not use derivatives for trading or speculative purposes. Derivative instruments are recognized in the consolidated balance sheets at fair value. Gains and losses resulting from changes in the fair value of derivative instruments that are not designated as hedging instruments for accounting purposes are recognized in other income (expense), net in the consolidated statements of operations in the period that the changes occur. Stock-Based Compensation Stock-based compensation expense primarily relates to restricted stock units (“RSU”), restricted common stock, stock options, and the Employee Stock Purchase Plan (“ESPP”). RSUs and restricted common stock are measured at the fair market value of the underlying stock at the grant date and the expense is recognized over the requisite service period. The fair value of stock options and ESPP shares granted to employees is estimated on the date of grant using the Black-Scholes option pricing model to determine the fair value of stock options on the date of grant. The Company estimates the expected term of stock options granted based on the simplified method and estimates the volatility of its common stock on the date of grant based on the average historical stock price volatility of comparable publicly-traded companies. The simplified method calculates the expected term as the mid-point between the weighted-average time to vesting and the contractual maturity. The simplified method is used as the Company does not have sufficient historical data regarding stock option exercises. The contractual term of the Company’s stock options is ten years. The Company accounts for forfeitures as they occur. The benefits of tax deductions in excess of recognized compensation costs are recognized in the income statement as a discrete item when an option exercise or a vesting and release of shares occurs. Prior to the Company’s IPO, the absence of an active market for the Company’s common stock required the Company’s board of directors, which includes members who possess extensive business, finance, and venture capital experience, to determine the fair value of its common stock for purposes of granting stock options and RSUs. The Company obtained contemporaneous third-party valuations to assist the board of directors in determining the fair value of the Company’s common stock. All stock options granted were exercisable at a price per share not less than the fair value of the shares of the Company’s common stock as determined by the board of directors (the “Fair Value”) underlying those stock options on their respective grant dates. Historically, substantially all of the Company’s RSUs vested upon the satisfaction of both a service-based vesting condition and liquidity-event performance-based vesting condition. The liquidity-event performance-based vesting condition for RSUs was satisfied upon the effectiveness of the Company’s IPO Registration Statement on December 9, 2020. Upon the Company’s IPO in December 2020, the Company recorded a cumulative one-time stock-based compensation expense of $2.8 billion, determined using the grant-date fair values. The remaining unrecognized stock-based compensation expense related to these RSUs is recorded over their remaining requisite service periods. Net Loss Per Share Attributable to Common Stockholders The Company applies the two-class method when computing net loss per share attributable to common stockholders when shares are issued that meet the definition of a participating security. The two-class method determines net income (loss) per share for each class of common stock and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires earnings available to common stockholders for the period to be allocated between common stock and participating securities based upon their respective rights to receive dividends as if all earnings for the period had been distributed. The Company’s previously outstanding redeemable convertible preferred stock was a participating security as the holders of such shares participated in dividends but did not contractually participate in the Company’s losses. Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, less weighted-average shares subject to repurchase. The diluted net loss per share is computed by giving effect to all potentially dilutive securities outstanding for the period. For periods in which the Company reports net losses, diluted net loss per share attributable to common stockholders is the same as basic net loss per share attributable to common stockholders, because potentially dilutive common shares are anti-dilutive. Comprehensive Loss Comprehensive loss consists of net loss and other comprehensive income (loss). Other comprehensive income (loss) reflects gains and losses that are recorded as a component of stockholders’ equity and are excluded from net loss. Other comprehensive income (loss) consists of foreign currency translation adjustments related to consolidation of foreign entities and unrealized gains (losses) on securities classified as available-for-sale. Contingencies The Company is subject to legal proceedings and claims that arise in the ordinary course of business. The Company accrues for losses associated with legal claims when such losses are probable and can be reasonably estimated. These accruals are adjusted as additional information becomes available or circumstances change. Recently Adopted Accounting Standards In January 2020, the Financial Accounting Standards Board (“FASB”) issued ASU No. 2020-01, Investments-Equity Securities (Topic 321), Investments-Equity Method and Joint Ventures (Topic 323), and Derivatives and Hedging (Topic 815): Clarifying the Interactions between Topic 321, Topic 323, and Topic 815, which clarifies the interaction of the accounting for equity securities under Topic 321 and investments accounted for under the equity method of accounting under Topic 323, and the accounting for certain forward contracts and purchased options accounted for under Topic 815. For public companies, the guidance was effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years. Early adoption was permitted. The Company adopted the standard on January 1, 2021. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. In August 2020, the FASB issued ASU 2020-06, Debt — Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging — Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity, which simplify the accounting for convertible instruments by reducing the number of accounting models available for convertible debt instruments. This guidance also eliminates the treasury stock method to calculate diluted earnings per share for convertible instruments and requires the use of the if-converted method. For public companies, the guidance is effective for fiscal years beginning after December 15, 2021, and interim periods within those fiscal years. Early adoption is permitted. The Company early adopted the standard on January 1, 2021 and applied this guidance to its convertible senior notes issued in March 2021. Refer to Note 10, Debt, for additional information. In October 2020, the FASB issued ASU 2020-08, Codification Improvements to Subtopic 310-20, Receivables — Nonrefundable Fees and Other Costs, which clarifies when an entity should assess whether a callable debt security is within the scope of accounting guidance, which impacts the amortization period for nonrefundable fees and other costs. For public companies, the guidance was effective for fiscal years beginning after December 15, 2020, and interim periods within those fiscal years. Upon adoption, the amendments are to be applied on a prospective basis as of the beginning of the period of adoption for existing or newly purchased callable debt securities. Early adoption was not permitted. The Company adopted the standard on January 1, 2021. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. In October 2021, the FASB issued ASU 2021-08, Business Combinations - Accounting for contract assets and contract liabilities from contracts with customers (Topic 805), which requires contract assets and contract liabilities acquired in a business combination to be recognized and measured by the acquirer on the acquisition date in accordance with Revenues from contracts with customers (Topic 606). For public companies, the guidance is effective for fiscal years beginning after December 15, 2022, and interim periods within those fiscal years. Early adoption is permitted. The Company early adopted the guidance upon issuance within the fourth quarter of 2021. The adoption of this guidance did not have a material impact on the Company’s consolidated financial statements. Recently Issued Accounting Standards Not Yet Adopted In March 2020, the FASB issued ASU 2020-04, Reference Rate Reform (Topic 848), which provides optional expedients and exceptions to contract modifications and hedging relationships that reference the London Interbank Offered Rate or another reference rate expected to be discontinued. The standard is effective upon issuance and may be applied at the beginning of the interim period that includes March 12, 2020 through December 31, 2022. In January 2021, the FASB issued ASU 2021-01, which clarified the scope of Topic 848 to include derivatives that are affected by a change in the interest rate used for margining, discounting, or contract price alignment that do not also reference London Interbank Offered Rate or another reference rate that is expected to be discontinued as a result of the reference rate reform. The standard is effective upon issuance and may be applied retroactively as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or prospectively to any new modifications within an interim period including or subsequent to January 7, 2021, up to the date that the financial statements are available to be issued. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In May 2021, the FASB issued ASU 2021-04, Earnings Per Share (Topic 260), Debt - Modifications and Extinguishments (Topic 470-50), Compensation - Stock Compensation (Topic 718), and Derivatives and Hedging - Contracts in Entity's Own Equity (Subtopic 815-40), which clarifies existing guidance for freestanding written call options which are equity classified and remain so after they are modified or exchanged in order to reduce diversity in practice. The standard is effective for public entities in fiscal years beginning after December 15, 2021, including interim periods within those fiscal years. Early adoption is permitted, including adoption in an interim period. The Company is evaluating the impact of adopting this guidance on its consolidated financial statements. There are other new accounting pronouncements issued by the FASB that the Company has adopted or will adopt, as applicable, and the Company does not believe any of these accounting pronouncements have had, or will have, a material impact on its consolidated financial statements or disclosures.

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