Obsolescence is the loss of an asset’s usefulness or value from causes other than physical wear and tear, which is why an asset in good working order can still be obsolete. Technological change, a shift in demand, a change of style or design, and a change in law or process all produce it. In US accounting and tax work the word does three distinct jobs: it is a named cause inside the depreciation allowance for fixed assets, it is one of the causes that pushes inventory off its cost basis, and in fair value measurement it is a wider term that takes in physical deterioration as well.
The consumer sense of the word, planned obsolescence, is a design and marketing question about products built so they need replacing sooner than they otherwise would, and it shares the word and none of the accounting treatment.
Obsolescence Inside the Depreciation Allowance
Federal tax law names obsolescence directly. The depreciation allowance includes an allowance for normal obsolescence, which should be taken into account to the extent that the expected useful life of property will be shortened by reason of it, and obsolescence may render an asset economically useless to the taxpayer regardless of its physical condition (26 CFR 1.167(a)-9). The statutory allowance that sentence sits inside is covered in depreciated.
The same section lists what it has in mind. Obsolescence is attributable to many causes, including technological improvements and reasonably foreseeable economic changes, and among these causes are normal progress of the arts and sciences, supersession or inadequacy brought about by developments in the industry, products, methods, markets, sources of supply and other like changes, and legislative or regulatory action (26 CFR 1.167(a)-9).
Two limits decide how often any of that reaches a return. A shorter life has to be shown rather than asserted, because a change to a new and shorter estimated useful life is permitted where the taxpayer shows obsolescence greater than had been assumed, and no such change is permitted merely because in the unsupported opinion of the taxpayer the property may become obsolete (26 CFR 1.167(a)-9). The second limit is that property reached by the Modified Accelerated Cost Recovery System has no estimated useful life to shorten in the first place, because its recovery period is assigned by statute instead of estimated, which is the ground MACRS covers.
Obsolescence Inside Inventory
The second context is stock rather than equipment, and the standard keeps obsolescence separate from physical deterioration there too. Under US GAAP a loss should be recognized whenever the utility of goods is impaired by damage, deterioration, obsolescence, changes in price levels or other causes (Accounting Research Bulletin No. 43, Chapter 4, paragraph 8). The goods are still on the shelf and still countable, so what has changed is the amount they can be carried at, not the quantity. How that departure from cost gets measured, and the tax rule for goods that can no longer be sold at normal prices, are worked through in shrinkage.
Functional, Economic and Physical Obsolescence
Fair value measurement splits the idea into components. Under the cost approach the amount required to acquire or construct a substitute asset of comparable utility is adjusted for obsolescence, and obsolescence there encompasses physical deterioration, functional or technological obsolescence, and economic or external obsolescence, which the standard treats as broader than depreciation for financial reporting purposes, an allocation of historical cost, or for tax purposes, which runs on specified service lives (FASB Statement No. 157, paragraph 18). That is a wider use of the word than the tax regulation’s, which keeps obsolescence separate from an asset’s physical condition.
The IRS uses the same three headings when a donated building is valued from replacement cost. Physical deterioration is the wear and tear on the building itself. Functional obsolescence usually appears in older buildings, with, for example, inadequate lighting, plumbing or heating, small rooms, or a poor floor plan. Economic obsolescence is outside forces causing the whole area to become less desirable (IRS, Publication 561, Rev. December 2025). The split is about where the cause sits: functional obsolescence is a fact about the asset itself, while economic or external obsolescence leaves the asset unchanged and moves everything around it.
What Obsolescence Is Commonly Confused With
Obsolescence is a cause, and depreciation is an allocation. Depreciation spreads an asset’s cost across the periods it serves and runs on its schedule whether or not anything has gone wrong, the mechanics of which sit in straight line depreciation. Obsolescence can change the estimate a book schedule was built on, but it is not the schedule.
Obsolescence is also the driver rather than the number. An impairment loss is a measured write-down of carrying amount, recognized only after a test says the carrying amount is not recoverable. Obsolescence is one of the reasons that test gets run, and the loss is what the test produces.
The third confusion is the cleanest. Obsolescence prices goods the business still has, while shrinkage counts goods it no longer has. One is a question about price, the other a question about quantity.
Common Questions
A client’s server is a common one. The hardware still runs, but the software the business depends on has stopped supporting it, so its remaining service to the business is shorter than the schedule assumed. Inventory gives the other version, a bin of parts for a model that is no longer made, still counted, still on the shelf, and no longer worth what it cost.
Accountably places trained offshore accountants and tax preparers inside US CPA and EA firms, and a firm can run a block of its own fixed asset and inventory work through a trial task before anything client facing depends on it.
