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.

As of January 1, 2024, the Company reorganized its previously reported North America, EMEA and International operating segments into two operating segments, Americas and International. See "Note 16. Information on Business Segments" for further details. Goodwill was re-allocated between our two new operating segments based on a relative fair value approach.

We determined that the Americas and International also represent our reporting units for goodwill impairment testing purposes. We identified the reorganization as a triggering event and performed a quantitative assessment of impairment for goodwill for each of our two new reporting units as of January 1, 2024. The result of our assessments for the Americas and International reporting units was that the fair value of each exceeded its carrying values and we concluded that no impairment existed. No further triggering events were identified during the quarter ended March 31, 2024.

Estimating the fair value of each reporting unit requires us to make assumptions and estimates regarding our future. We utilized a combination of 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 two reporting units.

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 of 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.

We have reclassified our goodwill by segment for the period presented below to reflect the change in operating segments. Changes in the net carrying amount of goodwill by segment were as follows:


(in millions)	ACCO Brands Americas			ACCO Brands International			Total
Balance at December 31, 2023	$	383.6		$	206.4		$	590.0
Foreign currency translation		(0.2	)		(12.7	)		(12.9	)
Balance at March 31, 2024	$	383.4		$	193.7		$	577.1

The gross carrying value and accumulated amortization by class of identifiable intangible assets as of March 31, 2024 and December 31, 2023, were as follows:


	March 31, 2024							December 31, 2023
(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	$	295.1	$	(44.5	)	$	250.6
Amortizable intangible assets:
Trade names		489.8		(145.1	)		344.7		497.1		(142.0	)		355.1
Customer and contractual relationships		358.0		(222.6	)		135.4		362.4		(221.3	)		141.1
Vendor relationships		82.4		(18.1	)		64.3		82.4		(16.7	)		65.7
Patents		8.0		(5.1	)		2.9		8.2		(5.0	)		3.2
Subtotal		938.2		(390.9	)		547.3		950.1		(385.0	)		565.1
Total identifiable intangibles	$	1,233.3	$	(435.4	)	$	797.9	$	1,245.2	$	(429.5	)	$	815.7

(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, 2024 and 2023 was $10.6 million and $10.9 million, respectively.

Estimated amortization expense for amortizable intangible assets, as of March 31, 2024, for the current year and the next five years is as follows:


(in millions)	2024		2025		2026		2027		2028		2029
Estimated amortization expense(2)	$	42.1	$	40.5	$	38.4	$	36.0	$	33.8	$	32.0

(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 quarter ended March 31, 2024, that would indicate it is more likely than not that an impairment loss has been incurred.