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Stock-based Compensation | 12 Months Ended
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Dec. 31, 2023
Stock-based Compensation |
Stock-based Compensation | 9. Stock-based Compensation 2017 Equity Incentive Plan The Rhythm Pharmaceuticals, Inc. 2017 Equity Incentive Plan (the “2017 Plan”) provides for the grant of incentive stock options, non-qualified stock options, stock appreciation rights, performance units, restricted stock awards, restricted stock units and stock grants to employees, consultants, advisors and directors of us or our affiliates, as determined by the board of directors. The number of shares authorized under the 2017 Plan increases on the first day of each calendar year, commencing on January 1, 2018 and ending on (and including) January 1, 2027, by an amount equal to 4% of the outstanding shares of stock outstanding as of the end of the immediately preceding fiscal year. On January 1, 2024, 2023 and 2022, 2,377,062, 2,264,497, and 2,011,343 shares, respectively, were added to the 2017 Plan. Notwithstanding the foregoing, the board of directors may act prior to January 1 for a given year to provide that there will be no such January 1 increase in the number of shares authorized under the 2017 Plan for such year, or that the increase in the number of shares authorized under the 2017 Plan for such year will be a lesser number than would otherwise occur pursuant to the preceding sentence. Shares of common stock issued upon the exercise of stock options are generally issued from new shares of the Company. The 2017 Plan provides that the exercise price of incentive stock options cannot be less than 100% of the fair market value of the common stock on the date of the award for participants who own less than 10% of the total combined voting power of stock of the Company, and not less than 110% for participants who own more than 10% of the Company's voting power. Awards granted under the 2017 Plan will vest over periods as determined by the Company's board of directors. For options granted to date, the exercise price equaled the fair value of the common stock as determined by the board of directors on the date of grant. As of December 31, 2023, an aggregate of 11,729,382 shares of common stock were authorized for issuance under the 2017 Plan, of which a total of approximately 4,187,953 shares of common stock remained available for future awards. In addition, a total of 7,541,429 shares of common stock reserved for issuance were subject to currently outstanding stock options, performance share units and restricted stock units granted under the Plan. 2022 Inducement Plan On February 9, 2022, the Company’s board of directors adopted the Rhythm Pharmaceuticals, Inc. 2022 Employment Inducement Plan (the “2022 Inducement Plan”), which became effective on such date without stockholder approval pursuant to Rule 5635(c)(4) of the Nasdaq Stock Market LLC listing rules (“Rule 5635(c)(4)”). The 2022 Inducement Plan provides for the grant of non-qualified stock options, stock appreciation rights, performance units, restricted stock awards, restricted stock units and stock grants. In accordance with Rule 5635(c)(4), awards under the 2022 Inducement Plan may only be made to a newly hired employee who has not previously been a member of the Company’s board of directors, or an employee who is being rehired following a bona fide period of non-employment by the Company or a subsidiary, as a material inducement to the employee’s entering into employment with the Company or its subsidiary. An aggregate of 1,000,000 shares of the Company’s common stock have been reserved for issuance under the 2022 Inducement Plan. The exercise price of stock options granted under the 2022 Inducement Plan will not be less than the fair market value of a share of the Company’s common stock on the grant date. Other terms of awards, including vesting requirements, are determined by the Company’s board of directors and are subject to the provisions of the 2022 Inducement Plan. Stock options granted to employees generally vest over a four-year period but may be granted with different vesting terms. Certain options may provide for accelerated vesting in the event of a change in control. Stock options granted under the 2022 Inducement Plan expire no more than 10 years from the date of grant. As of December 31, 2023, there were 526,177 stock option awards outstanding, 233,719 restricted stock unit awards outstanding and 179,925 shares of common stock available for future grant under the 2022 Inducement Plan. ​ 2017 Employee Stock Purchase Plan The Company maintains the Rhythm Pharmaceuticals, Inc. 2017 Employee Stock Purchase Plan, (the “2017 ESPP”), which became effective in connection with the completion of the Company’s IPO in October 2017. As of December 31, 2023, a total of 1,323,026 shares of common stock were reserved for issuance under the 2017 ESPP. In addition, the number of shares authorized under the 2017 ESPP increases on the first day of each calendar year, commencing on January 1, 2019 and ending on (and including) January 1, 2027, by an amount equal to the lesser of 1% of outstanding shares as of the end of the immediately preceding fiscal year. On January 1, 2023, 2022 and 2021, 0, 502,835 and 0 shares, respectively, were added to the 2017 ESPP. Notwithstanding the foregoing, the board of directors may act prior to January 1 of a given year to provide that there will be no such January 1 increase in the number of shares authorized under the 2017 ESPP for such year, or that the increase in the number of shares authorized under the 2017 ESPP for such year will be a lesser number than would otherwise occur pursuant to the preceding sentence. The board of directors elected not to increase the number of shares available under the 2017 ESPP on January 1, 2024 and 2023. During the years ended December 31, 2023, 2022 and 2021, shares of 49,819, 92,932, and 38,051 were issued under the 2017 ESPP. ​ The purchase price of common stock under our ESPP is equal to 85.0% of the lower of (i) the market value per share of the common stock on the first business day of an offering period or (ii) the market value per share of the common stock on the purchase date. The fair value of the discounted purchases made under our ESPP is calculated using the Black-Scholes model. The fair value of the look-back provision plus the 15.0% discount is recognized as compensation expense over the 6 month purchase period. ​ Stock Options The Company estimates the fair value of stock option awards to employees and non-employees using the Black-Scholes option-pricing model, which requires the input of subjective assumptions, including (a) the expected volatility of the underlying common stock, (b) the expected term of the award, (c) the risk-free interest rate, and (d) expected dividends. The Company bases its estimate of expected volatility using a blend of its stock price history for the length of time it has market data for its stock and using the historical volatility of a group of companies in the pharmaceutical and biotechnology industries in a similar stage of development as the Company that are publicly traded. For these analyses, the Company selected companies with comparable characteristics to its own including enterprise value, risk profiles and with historical share price information sufficient to meet the expected life of the stock-based awards. The Company computes the historical volatility data using the daily closing prices for the selected companies' shares during the equivalent period of the calculated expected term of its stock-based awards. The Company will continue to apply this process until a sufficient amount of historical information regarding the volatility of its own stock price becomes available. The Company estimated the expected life of its employee stock options using the “simplified” method, whereby, the expected life equals the average of the vesting term and the original contractual term of the option. The risk-free interest rates for periods within the expected life of the option are based on the U.S. Treasury yield curve in effect during the period the options were granted. We have elected to account for forfeitures as they occur. The grant date fair value of awards subject to service-based vesting is recognized ratably over the requisite service period, which is generally the vesting period of the respective awards. The Company's stock option awards typically vest over a service period that ranges from one to four years and includes awards with one year cliff vesting followed by ratable monthly and quarterly vesting thereafter and ratable monthly and quarterly vesting beginning on the grant date. During the years ended December 31, 2023, 2022 and 2021, the Company granted 842,528, 1,929,345, and 1,678,230 stock option awards pursuant to the 2017 Plan to certain directors, employees and non-employees, respectively. Using the Black-Scholes option pricing model, the weighted-average grant date fair value relating to outstanding stock options granted under the 2017 Plan during the years ended December 31, 2023, 2022 and 2021 was $17.72, $4.14, and $15.69, respectively. During the years ended December 31, 2023, 2022 and 2021, the Company granted 229,360, 347,985, and 0 stock option awards pursuant to the 2022 Inducement Plan. Using the Black-Scholes option pricing model, the weighted-average grant date fair value relating to outstanding stock options granted under the Company’s stock option plan during the years ended December 31, 2023, 2022 and 2021 was $15.30, $13.05, and $0, respectively. The fair value of stock options granted to employees and directors was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year ended
​ | ​ | December 31,
​ | ​ | 2023 |  | ​ | 2022 |  | ​ | 2021 |
Risk‑free interest rate | ​ | 2.35 | % | ​ | 2.19 | % | ​ | 0.79 | %
Expected term (in years) | ​ | 6.11 | ​ | ​ | 6.11 | ​ | ​ | 6.11 | ​
Expected volatility | ​ | 76.11 | % | ​ | 69.16 | % | ​ | 69.80 | %
Expected dividend yield | ​ | — | ​ | ​ | — | ​ | ​ | — | ​
​ ​ A summary of the Company's stock option activity for the year ended December 31, 2023 is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ |  | ​ |  | ​ |  | ​ | Weighted‑ | ​ |  | ​
​ | ​ | ​ | ​ | ​ | ​ | Weighted- | ​ | ​ | Average | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | Average | ​ | ​ | Remaining | ​ | ​ | Aggregate
​ | ​ | ​ | ​ | Number of | ​ | Exercise | ​ | ​ | Contractual | ​ | ​ | Intrinsic
​ | ​ | ​ | ​ | Options | ​ | Price | ​ | ​ | Term | ​ | ​ | Value
Outstanding as of December 31, 2022 |  | 6,374,544 | ​ | $ | 17.85 | ​ | ​ | 7.73 | ​ | $ | 73,994
Granted | ​ | ​ |  | 1,053,888 | ​ | $ | 25.42 | ​ |  | — | ​ | $ | —
Exercised | ​ | ​ |  | (529,854) | ​ | $ | 14.09 | ​ |  | — | ​ | $ | 9,225
Cancelled | ​ | ​ |  | (347,553) | ​ | $ | 21.23 | ​ |  | — | ​ | $ | —
Outstanding as of December 31, 2023 |  | 6,551,025 | ​ | $ | 19.19 | ​ | ​ | 7.23 | ​ | $ | 175,419
Options exercisable at December 31, 2023 |  | 3,936,040 | ​ | $ | 19.77 | ​ | ​ | 6.54 | ​ | $ | 103,122
​ Restricted Stock Units ​ The Company may grant restricted stock units (“RSUs”) to employees and nonemployee directors under the 2017 Plan and to employees under the 2022 Inducement Plan. Each RSU represents a right to receive one share of the Company's common stock upon the completion of a specific period of continued service. RSU awards granted are valued at the market price of the Company's common stock on the date of grant. The Company recognizes stock-based compensation expense for the fair values of these RSUs on a straight-line basis over the requisite service period of these awards. A summary of the Company's restricted stock unit activity for the year ended December 31, 2023 is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ |  | ​ |  | ​
​ | ​ | ​ | ​ | ​ | ​ | Weighted-
​ | ​ | ​ | ​ | ​ | ​ | Average
​ | ​ | ​ | ​ | Number of | ​ | Grant Date
​ | ​ | ​ | ​ | RSUs | ​ | Fair Value
Unvested as of December 31, 2022 |  | 774,166 | ​ | $ | 12.18
Granted | ​ | ​ |  | 643,028 | ​ |  | 24.97
Vested | ​ | ​ |  | (214,837) | ​ |  | 14.30
Cancelled | ​ | ​ |  | (97,750) | ​ |  | 15.61
Unvested as of December 31, 2023 |  | 1,104,607 | ​ | $ | 17.44
​ As of December 31, 2023, the aggregate intrinsic value of unvested RSUs was $50,779. ​ Performance Stock Units ​ In November 2021, the Company granted up to a maximum of 956,145 performance stock units (“PSUs”) to employees under the 2017 Plan. Each PSU represents a right to receive one share of the Company's common stock upon vesting. The performance-based stock units granted in 2021 will vest on December 31, 2023 based upon i) continued service through the vesting date and (ii) the achievement of specific clinical development and regulatory performance events, as approved by the compensation committee. PSU awards granted are valued at the market price of the Company's common stock on the date of grant. The Company recognizes stock-based compensation expense for the fair value of these PSUs for the awards that are probable of vesting over the service period. During each financial period, management estimates the probable number of PSU’s that would vest until the ultimate achievement of the performance goal is known. At December 31, 2023, the Company estimates that 90.0% of the PSUs granted will be eligible to vest in the quarter ended March 31, 2024. ​ A summary of the Company's performance stock unit activity for the year ended December 31, 2023 is as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ |  | ​ |  | ​
​ | ​ | ​ | ​ | ​ | ​ | Weighted-
​ | ​ | ​ | ​ | ​ | ​ | Average
​ | ​ | ​ | ​ | Number of | ​ | Grant Date
​ | ​ | ​ | ​ | PSUs | ​ | Fair Value
Unvested as of December 31, 2022 |  | 804,797 | ​ | $ | 13.24
Granted | ​ | ​ |  | — | ​ |  | —
Vested | ​ | ​ |  | — | ​ |  | —
Cancelled | ​ | ​ |  | (223,451) | ​ |  | 13.24
Unvested as of December 31, 2023 |  | 581,346 | ​ | $ | 13.24
​ ​ The following table summarizes the classification of the Company's stock-based compensation expenses related to stock options, restricted stock units, performance stock units and the employee stock purchase plan recognized in the Company's consolidated statements of operations and comprehensive loss. ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended
​ | ​ | December 31,
​ |  | 2023 | ​ | 2022 | ​ | 2021
Research and development | ​ | $ | 8,449 | ​ | $ | 5,814 | ​ | $ | 7,687
Selling, general, and administrative | ​ |  | 24,104 | ​ |  | 14,017 | ​ |  | 13,117
Total | ​ | $ | 32,553 | ​ | $ | 19,831 | ​ | $ | 20,804
​ Stock-based compensation expense by award type recognized during the years ended December 31, 2023, 2022 and 2021 was as follows: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Year Ended
​ | ​ | December 31,
​ |  | 2023 | ​ | 2022 | ​ | 2021
Stock options | ​ | $ | 17,671 | ​ | $ | 15,477 | ​ | $ | 17,988
Employees stock purchase plan | ​ | ​ | 581 | ​ | ​ | 408 | ​ | ​ | 310
Restricted stock units | ​ |  | 5,998 | ​ |  | 2,918 | ​ |  | 1,924
Performance stock units | ​ | ​ | 8,303 | ​ | ​ | 1,028 | ​ | ​ | 582
Total | ​ | $ | 32,553 | ​ | $ | 19,831 | ​ | $ | 20,804
​ As of December 31, 2023, the Company has unrecognized compensation cost of $27,322 related to non-vested employee, non-employee and director stock option awards under all equity plans that are expected to be recognized over a weighted-average period of 2.07 years. The Company has unrecognized compensation cost of $16,880 related to non-vested employee restricted stock unit and performance stock unit awards under all equity plans that are expected to be recognized over a weighted-average period of 2.63 years.

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