Accounting for depreciation with the straight line method, sum of years digits method and declining balance method, example shows how to calaculate depreciation expense using each of these methods, for (1) straight line method calculate the full year based on (1/1) fiscal year determine the depreciation charge (cost minus salvage value divided by service life equals the depreciation charge per period, with straight line depreciation, depreciation expense is a function of time rather than a function of usage, (2) sum of years digit method calculate the depreciation fraction as the sum of years for the depreciation period or as the equation (n(n+1)/2 = sum of years), use the sum of years as the denominator dividing it into the remaining life and multiplying the fractional amount times the depreciation base equals the depreciation for the period, (3) using the declining balance method do not deduct the salvage value from the cost for computing the depreciation base, the depreciation rate is based on a percentage (multiple) of the straight line depreciation rate, double declining balance would be two times the straight line depreciation rate, depreciation expense for the period is calculated by multiplying the declining balance rate times the book value (carrying value) for the asset for each period, detailed calculations by Allen Mursau