Accelerated Depreciation

Double-declining balance applies a fixed rate to a declining base. The rate is two divided by the useful life in years, and it is applied each period to the asset's beginning net book value, not to the depreciable base. Salvage value is ignored in the arithmetic but acts as a floor: depreciation stops once carrying amount reaches estimated residual value, and the final year's charge is often plugged to land exactly on that floor. Many firms switch to straight-line on the remaining book value once the straight-line charge would exceed the declining-balance charge.

Sum-of-the-years'-digits works from a fraction rather than a rate. The denominator is the sum of the integers from one to the useful life, which equals the life times the life plus one, divided by two. The numerator is the years of life remaining at the start of the period. That fraction is multiplied by cost less salvage, so residual value enters directly. Both methods leave lifetime expense identical to straight-line; only the timing differs.

On the income statement, early-year depreciation is larger, so operating income, net income and margins are lower than under straight-line, and the pattern reverses in later years without any change in the asset's economics. On the balance sheet, accumulated depreciation builds faster and net PP&E is smaller, which shrinks total assets and equity and mechanically lifts asset turnover and leverage measured on book values.

Cash flow from operations is unaffected in the absence of tax consequences, because depreciation is a non-cash charge added back in the indirect method. Where the method is also used for tax, the timing shift is real cash: taxes paid fall early and rise later, and the difference between the tax base and the carrying amount of the asset creates a taxable temporary difference. That difference is recognised as a deferred tax liability, which unwinds as the tax depreciation on the asset runs out while book depreciation continues.

Most jurisdictions prescribe capital allowance or cost-recovery systems for tax that are more aggressive than the reporting method a firm chooses for shareholders, so financial statements and tax returns diverge routinely. Capital-intensive sectors such as telecommunications, utilities, shipping, mining and semiconductor manufacturing therefore carry large deferred tax liabilities that are essentially a running record of that timing gap.

For comparative work the practical issue is that depreciation method, useful life and salvage assumptions are all managerial estimates disclosed in the notes rather than dictated by the standards. Two otherwise identical firms can report very different net income and return on assets. Analysts read the PP&E and tax notes, compare average useful lives and the ratio of accumulated depreciation to gross PP&E to judge relative asset age and conservatism, and adjust or normalise depreciation before comparing margins and returns across peers.

Expect to compute a single year's charge under double-declining balance, including the salvage floor and the crossover to straight-line, and under sum-of-the-years'-digits with the correct remaining-life numerator. Be ready to state the carrying amount at any date, since gain or loss on a later disposal depends on it, and to explain why an early sale of an accelerated-depreciated asset tends to produce a larger accounting gain.

Equally important is directional reasoning without a calculator: identify which method a firm uses, then say how switching would move net income, total assets, equity, return on assets, return on equity, asset turnover, the fixed asset turnover ratio and cash flow from operations in early versus late years. Finally, connect the method choice to deferred taxes, and be able to distinguish a timing difference that reverses from a permanent difference that never does.