Are useful life and amortisation period the same thing?

For most finite-life intangibles under IAS 38 (UK and global) and ASC 350 (US), yes — the amortisation period equals the assessed useful life. The two concepts diverge in three principal cases: (a) indefinite-life assets, which are not amortised at all; (b) where a legal or contractual cap is shorter than the economic life, in which case the amortisation period is capped per IAS 38.94; and (c) where the entity elects a shorter amortisation period under prudence. Under FRS 102 Section 18 (UK), indefinite life is not permitted, and useful life is capped at 10 years where it cannot be reliably estimated.

What is an indefinite useful life under IAS 38?

An intangible has an indefinite useful life when there is no foreseeable limit to the period over which the asset will generate net cash inflows for the entity. Indefinite is not infinite — it means the entity cannot identify an end point given current expectations. The asset is not amortised but is tested annually for impairment under IAS 36 (UK and global). The classic example is an acquired brand with sustained market position and no contractual or technological ceiling. FRS 102 Section 18 (UK) does not permit indefinite life.

How often must useful life be reviewed?

Under IAS 38.104 (UK and global), useful life and amortisation method must be reviewed at each financial year end. If the expected pattern of consumption of the asset's economic benefits has changed, the amortisation method is adjusted; if the useful life estimate has changed, the remaining carrying value is spread over the revised remaining life prospectively. Indefinite-life assets are reassessed each period under IAS 38.109 to confirm the indefinite assessment remains supported.

What happens if useful life changes from finite to indefinite?

This is rare and tightly constrained. The reclassification can only occur where new evidence supports an indefinite assessment. The cumulative amortisation already charged is not reversed. From the date of reclassification, no further amortisation is recorded; the asset is tested annually for impairment under IAS 36. The change in estimate is disclosed in the notes. Audit attention concentrates on whether the new indefinite assessment is genuinely supported or is being used to mask a depreciating asset.

Can an amortisation period be shorter than the useful life?

Yes, in narrow circumstances. The most common case is where the entity elects to amortise over a tax-aligned period (where tax law specifies a maximum amortisation period that is shorter than the economic useful life). Another case is prudence — where management judgement supports a faster recognition pattern, even though the asset's economic life is longer. Any divergence between useful life and amortisation period must be documented and justified; audit teams will not accept "we chose 5 years" without a basis.

How does FRS 102 differ from IAS 38 on useful life?

FRS 102 Section 18 (UK) requires every intangible asset to have a finite useful life. Indefinite-life classification is not permitted. Where useful life cannot be reliably estimated, the maximum is 10 years. This is a material divergence from IAS 38 (UK and global IFRS), which permits indefinite life for qualifying assets. Under FRS 102, every acquired brand, acquired customer relationship, or acquired technology is amortised; under IAS 38, the same asset might be classified as indefinite-life and tested annually for impairment instead.

What documentation does the auditor expect for useful life?

At recognition: the legal, contractual, and economic factors weighed in arriving at the estimate, with cross-reference to comparable assets, industry life cycles, and known obsolescence trends. At each year end: the annual review outcome — either confirmation that the prior estimate remains supported (with current-year evidence) or a documented revision with prospective adjustment. The audit file should also show the link between useful life and the amortisation period applied, including justification for any divergence. The strongest position is documented at recognition, reassessed every year, and supported by external evidence.

How does this connect to impairment testing?

Finite-life intangibles are tested for impairment under IAS 36 (UK and global) when indicators are present — declining performance, market deterioration, technological change. Indefinite-life intangibles and goodwill are tested annually regardless of indicators. The useful life assessment drives which test applies: a finite-life asset with a 7-year amortisation period faces trigger-based testing; an indefinite-life brand faces annual testing. Where useful life is reclassified from indefinite to finite, the asset moves from annual testing to trigger-based testing from the reclassification date.

concept

Useful Life vs Amortisation Period — How They Differ and When Auditors Care

Useful life is the economic period over which an intangible generates benefit; amortisation period is the accounting horizon over which carrying value is written down. They coincide in most cases — but the divergence cases are exactly where audit attention concentrates.

Useful life and amortisation period are routinely treated as the same thing — but they are two distinct concepts that happen to coincide in most cases. Useful life is the economic period over which an intangible asset is expected to generate benefit. Amortisation period is the accounting horizon over which the cost is written down to profit and loss. The divergence cases — indefinite life, legal cap, prudence election, FRS 102 ceiling — are where the CFO has to be able to explain the choice.

Criteria	Useful Life	Amortisation Period
Definition	Economic period over which the asset generates benefit	Accounting period over which the carrying value is written down
Primary anchor	IAS 38.8 (UK and global); ASC 350-30-35 (US)	IAS 38.97 (UK and global); ASC 350-30-35 (US)
Can be indefinite?	Yes, under IAS 38 (UK and global) and ASC 350 (US) where there is no foreseeable limit	No — by definition, an indefinite-life asset is not amortised
Determined by	Legal life capped by economic life; whichever is shorter	Equal to useful life by default; can be shorter in narrow cases
Review cadence	At each financial year end (IAS 38.104 UK and global)	Adjusted prospectively when useful life estimate changes
Treatment under FRS 102 Section 18 (UK)	Must be finite; maximum 10 years if not reliably estimable	Must be finite; amortisation period bounded by the 10-year cap where applicable
What changes when estimate revised	Reassessment triggers prospective amortisation adjustment	Remaining carrying value spread over revised remaining useful life
Audit focus	Documentation of legal, contractual, and economic factors at recognition	Consistency between useful life and amortisation period; justification of any divergence
Typical range (finite-life intangibles)	3-20 years	3-20 years (mirror of useful life in most cases)
Where the two diverge	Indefinite life under IAS 38 (UK and global); legal cap; prudence election	Mirrors useful life unless one of the divergence cases applies
Impairment interaction	Annual impairment test for indefinite-life assets; trigger-based for finite-life	Amortising assets tested when indicators present; non-amortising assets tested annually

When to Use Each Approach

Useful Life

Setting the economic horizon at acquisition or recognition
Annual reassessment of an existing intangible's expected benefit period
Indefinite-life classification under IAS 38 (UK and global) or ASC 350 (US)
Driving the impairment testing regime (annual vs trigger-based)

Amortisation Period

Calculating the annual amortisation charge
Setting the systematic allocation under IAS 38.97 (UK and global)
Applying a legal or contractual cap shorter than economic life
Aligning with tax amortisation periods where prudence supports a shorter horizon

Our Verdict

For most finite-life intangibles the two concepts coincide. They diverge in three principal cases: indefinite-life assets (no amortisation period), legal caps shorter than economic life, and prudence elections. Auditors will accept any of these patterns when documented; they will challenge any divergence that is not.

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Useful Life vs Amortisation Period — How They Differ and When Auditors Care

When to Use Each Approach

Useful Life

Amortisation Period

Our Verdict

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