Which depreciation method is not based on accounting periods?

The units of production method is the depreciation method that is not based on accounting periods but rather on the actual usage of the asset. This approach calculates depreciation based on the asset's activity level, such as the number of units produced or hours used. As a result, the depreciation expense varies with the level of production, making it more related to the asset's operational effectiveness rather than fixed time periods.

In contrast, the other methods outlined—straight-line, declining balance, and sum-of-the-years'-digits—are all tied to specific accounting periods. For instance, the straight-line method allocates an equal amount of depreciation expense for each period over the asset's useful life, while the declining balance and sum-of-the-years'-digits methods provide accelerated depreciation, typically favoring the earlier years and relying on a formula that incorporates time as a factor. This clear distinction in focus—usage versus time—sets the units of production method apart as being not based on accounting periods.