We test goodwill for impairment at least annually as of our measurement date of May 31st and on an interim basis if an event or circumstance indicates that it is more likely than not that an impairment loss has been incurred. We did not identify a triggering event during the three months ended March 31, 2023, that would indicate it is more likely than not that an impairment loss has been incurred.

We believe the assumptions used in our goodwill impairment analysis are appropriate and result in reasonable estimates of the implied fair value of each reporting unit. However, given the economic environment and the uncertainties regarding the impact on our business, there can be no assurance that our estimates and assumptions, made for purposes of our goodwill impairment testing, will prove to be an accurate prediction of the future. If our assumptions regarding future performance are not achieved, we may be required to record additional goodwill impairment charges in future periods.

Estimating the fair value of each reporting unit requires us to make assumptions and estimates regarding our future. We utilized a combination of both a discounted cash flows and market approach. The financial projections used in the valuation models reflected management's assumptions regarding revenue growth rates, economic and market trends, cost structure, discount rate, and other expectations about the anticipated short-term and long-term operating results for each of our three reporting units.

Changes in the net carrying amount of goodwill by segment were as follows:


(in millions)		ACCO Brands North America			ACCO Brands EMEA				ACCO Brands International			Total
Balance at December 31, 2022	$		348.0	$		145.6		$		177.9	$		671.5
Foreign currency translation			—			(0.2	)			0.6			0.4
Balance at March 31, 2023	$		348.0	$		145.4		$		178.5	$		671.9

The gross carrying value and accumulated amortization by class of identifiable intangible assets as of March 31, 2023 and December 31, 2022, were as follows:


		March 31, 2023										December 31, 2022
(in millions)		Gross Carrying Amounts			Accumulated Amortization				Net Book Value			Gross Carrying Amounts			Accumulated Amortization				Net Book Value
Indefinite-lived intangible assets:
Trade names(1)	$		295.1	$		(44.5	)	$		250.6	$		410.6	$		(44.5	)	$		366.1
Amortizable intangible assets:
Trade names			491.0			(127.9	)			363.1			369.7			(123.0	)			246.7
Customer and contractual relationships			359.5			(204.7	)			154.8			356.9			(198.2	)			158.7
Vendor relationships			82.4			(12.6	)			69.8			82.4			(11.2	)			71.2
Patents			8.2			(4.1	)			4.1			8.1			(3.8	)			4.3
Subtotal			941.1			(349.3	)			591.8			817.1			(336.2	)			480.9
Total identifiable intangibles	$		1,236.2	$		(393.8	)	$		842.4	$		1,227.7	$		(380.7	)	$		847.0

(1)

Accumulated amortization prior to the adoption of authoritative guidance on goodwill and other intangible assets, at which time further amortization ceased.

The Company's intangible amortization expense for the three months ended March 31, 2023 and 2022 was $10.9 million and $11.1 million, respectively.

Estimated amortization expense for amortizable intangible assets, as of March 31, 2023, for the current year and the next five years is as follows:


(in millions)		2023			2024			2025			2026			2027			2028
Estimated amortization expense(2)	$		43.6	$		42.0	$		40.4	$		38.3	$		35.9	$		33.7

(2)

Actual amounts of amortization expense may differ from estimated amounts due to changes in foreign currency exchange rates, additional intangible asset acquisitions, impairment of intangible assets, accelerated amortization of intangible assets and other events.

We test indefinite-lived intangibles for impairment at least annually as of our measurement date of May 31st and on an interim basis if an event or circumstance indicates that it is more likely than not that an impairment loss has been incurred. We did not identify a triggering event during the three months ended March 31, 2023, that would indicate it is more likely than not that an impairment loss has been incurred.

Estimating the fair value of each indefinite-lived intangible requires us to make assumptions and estimates regarding our future. We utilize a relief-from-royalty discounted cash flows approach to estimate fair values. Key inputs and assumptions involved include the estimated near-term revenue growth, long-term growth rate, royalty rate, and discount rate.

As of December 31, 2022, we changed the indefinite-lived Leitz® trade name to an amortizable intangible asset. The change was made as a result of decisions regarding the Company's future use of the trade name. The Company began amortizing the Leitz® trade name on a straight-line basis over a life of 30 years effective January 1, 2023.