In accountancy, depreciation refers to two aspects of the same concept:The former affects the balance sheet of a business or entity, and the latter affects the net income that they report. Generally the cost is allocated, as depreciation expense, among the periods in which the asset is expected to be used. This expense is recognized by businesses for financial reporting and tax purposes. Methods of computing depreciation, and the periods over which assets are depreciated, may vary between asset types within the same business and may vary for tax purposes. These may be specified by law or accounting standards, which may vary by country. There are several standard methods of computing depreciation expense, including fixed percentage, straight line, and declining balance methods. Depreciation expense generally begins when the asset is placed in service. For example, a depreciation expense of 100 per year for 5 years may be recognized for an asset costing 500.