Depreciation is a term used in accounting, economics and finance with reference to the fact that assets with finite lives lose value over time.

In accounting, depreciation is a term used to describe any method of attributing the historical or purchase cost of an asset, across its useful life, roughly corresponding to normal wear and tear.[1] It is of most use when dealing with assets of a short, fixed service life, and which is an example of applying the matching principle as per generally accepted accounting principles. Depreciation in accounting is often mistakenly seen as a basis for recognizing impairment of an asset, but unexpected changes in value, were seen as significant enough to account for, are handled through write-downs or similar techniques which adjust the book value of the asset to reflect its current value. Therefore, it is important to recognize that depreciation, when used as a technical accounting term, is the allocation of the historical cost of an asset across time periods when the asset is employed to generate revenues. This process of cost allocation has little or no direct relationship to the market value or current selling price of the asset, it is simply the recognition that a portion of the asset's cost--the portion that will never be recuperated through re-sale or disposal of the asset--was "used up" in the generation of revenues for that time period.

The use of depreciation affects the financial statements and in some countries the taxes of companies and individuals. The recording of depreciation will cause an expense to be recognized, thereby lowering stated profits on the income statement, while the net value of the asset (the portion of the historical cost of the asset that remains to provide future value to the company) will decline on the balance sheet. Depreciation reported for accounting and tax purposes may differ substantially.

Depreciation and its related concept, amortization (generally, the depreciation of intangible assets), are non-cash expenses. Neither depreciation nor amortization will directly affect the cash flow of a company, as both are accounting representations of expenses attributable to a given period. In accounting statements, depreciation may neither figure in the cash flow statement, or may be "added back" to net income (along with other items) to derive the operating cash flow.[2] Depreciation recognized for tax purposes will, however, affect the cash flow of the company, as tax depreciation will reduce taxable profits; there is generally no requirement that treatment of depreciation for tax and accounting purposes be identical. Where depreciation is shown on accounting statements, the figure usually does not relate to depreciation for tax purposes.