When calculating depreciation under the double declining method, what affects the depreciation base each year?

When using the double declining balance method of depreciation, the depreciation base that is used to calculate depreciation each year is the book value at the beginning of that year. This method applies a constant depreciation rate to the remaining book value of the asset, rather than its original cost or purchase price.

As depreciation is calculated, the book value decreases each year because the accumulated depreciation reduces the value of the asset on the balance sheet. This continuous reduction in book value means that the depreciation expense will decrease over the years, reflecting the asset's declining value.

The other choices do not accurately represent how the depreciation base is determined in this method. The original cost does not change and is not used in subsequent calculations after the first year. The estimated residual value is important in other depreciation methods but does not directly affect the depreciation base for calculating double declining balance depreciation. Lastly, only considering the purchase price ignores the ongoing effect of accumulated depreciation on the asset's book value each year.