The formula is as follows:
(1) Annual depreciation rate = 2 ÷ estimated depreciable life × 100%, and annual depreciation = net book value of fixed assets at the beginning of the period × annual depreciation rate.
(2) Monthly depreciation rate = annual depreciation rate ÷ 12
(3) Monthly depreciation amount = net depreciated value of fixed assets at the beginning of the year × monthly depreciation rate
(4) Net book value of fixed assets at the beginning of the year = original value of fixed assets - accumulated depreciation
Fixed assets subject to the double-declining-balance method should be depreciated over a number of years before the expiration of depreciation years of the fixed assets (when the depreciation using the straight-line method is greater than or equal to the depreciation using the double-declining-balance method), the net book value of the fixed assets less the estimated net salvage value should be amortized equally.