Depreciation expense is the allocated portion of the cost of a company's fixed assets that is appropriate for the accounting period indicated on the company's income statement. For instance, if a company had paid $2,400,000 for its office building (excluding land) and the building has an estimated useful life of 40 years, each monthly income statement will report straight-line depreciation expense of $5,000 for 480 months. [However, the allocated cost of the fixed assets used in manufacturing will be part of the manufacturing overhead which will become part of the cost of the products manufactured.]

Depreciation expense is referred to as a noncash expense because the recurring, monthly depreciation entry (a debit to Depreciation Expense and a credit to Accumulated Depreciation) does not involve a cash payment. As a result, the statement of cash flows prepared under the indirect method will add depreciation expense to the amount of net income.

The common methods for computing depreciation expense include straight-line, double-declining balance, sum-of-the-years digits, and units of production or activity.