Plain definition
Useful life is the period over which a business expects to use an asset or the number of units it expects to obtain from it. It is an accounting estimate of consumption, not necessarily the physical life, warranty period, or loan term. It drives depreciation or amortisation and should reflect expected use, maintenance, technological change, legal rights, and disposal plans.
Illustrative example
A machine can physically run for ten years, but a company expects to replace it after five because a new process will make it uneconomic. If the evidence supports five years, finance uses five as the useful life for depreciation rather than ten. The manager must revisit the estimate if the replacement plan is cancelled or usage changes.
Useful life is reviewed when facts indicate change; revising an estimate is not the same as correcting a past error. The applicable framework determines how changes are reflected.
Why it matters
An unrealistically long useful life spreads cost too slowly and inflates profit and asset value. An unrealistically short life can depress current profit and make a viable investment appear poor. Both can distort capital-allocation decisions.
Practical consequence
For each material asset, document expected use, maintenance plan, technology risk, legal term, replacement intention, and evidence for the selected life. Compare actual utilisation and disposal history with estimates annually. Require review approval for changes and explain their effect to management rather than changing lives merely to meet a target.