Abstract The article discusses the concept of declining-balance depreciation. The article consists of three formulas which can be useful where computations as to periodic or accumulated depreciation under a declining-balance method are required. Just as a premature disclosure of the guilty party of a good mystery can spoil the plot, so can the disclosure of the derivation of a formula spoil the fun for those interested in such. The calculation of periodic declining-balance depreciation is provided by a formula. For purposes of illustration, the author assumes that an asset costing $10,000 has an estimated life of twenty years, or a ten percent rate for double-declining balance depreciation. Accumulated depreciation at the beginning of the nth year is computed by the formula, when declining-balance depreciation is used. The article presents a table which indicates the undepreciated balance of the asset at the end of the period. Where a large number of unit accounts are maintained and tests are to be made of the computations of depreciation, similar tables with appropriate values can be constructed to facilitate such test checks.