What is the straight line method of depreciation?

Straight Line Depreciation Method

Straight line method depreciates cost evenly throughout the useful life of the fixed asset. Straight line depreciation is calculated as follows:

Depreciation per annum = (Cost - Residual Value) / Useful Life

Where:

Cost includes the initial and any subsequent capital expenditure.

Residual Value is the estimated scrap value at the end of the useful life of the asset. As the residual value is expected to be recovered at the end of an asset's useful life, there is no need to charge the portion of cost equaling the residual value?

Useful Life is the estimated time period an asset is expected to be used from the time it is available for use to the time of its disposal or termination of use. Useful life is normally calculated in units of years but it may be calculated based on an alternative basis. Useful life of an oil extraction company may for example be the estimated oil reserves.

In straight line depreciation method, depreciation is charged uniformly over the life of an asset. We first subtract residual value of the asset from its cost to obtain the depreciable amount. The depreciable amount is then divided by the useful life of the asset in number of accounting periods to obtain depreciation expense per accounting period. Due to the simplicity of the straight line method of depreciation, it is the most commonly used depreciation method.

The formula to calculate the straight-line depreciation of an asset for a full accounting period is: