The common characteristic of the double declining balance method and the sum of years method is that the depreciation amount calculated in the early period of the service life of fixed assets is large, and the depreciation amount calculated in the later period is gradually reduced, so as to achieve the purpose of accelerating the compensation of fixed production cost in the service life, so they are also called accelerated depreciation method. Under the accelerated depreciation method, in order to simplify the calculation, the annual depreciation is usually calculated first, and then the annual depreciation divided by 12 to calculate the monthly depreciation.The double declining balance method is a method to calculate the depreciation of fixed assets according to the frame value of fixed assets at the beginning of each period (that is, the original value minus accumulated depreciation) multiplied by the linear depreciation rate of two times without considering the estimated net salvage value of fixed assets.