The calculation for annual depreciation using the straight-line depreciation method is

A) Initial cost / Estimated useful life
B) Depreciable cost / Estimated useful life
C) Depreciable cost × Estimated useful life
D) Initial cost × Estimated useful life

The straight-line depreciation method calculates annual depreciation by dividing the depreciable cost (initial cost minus salvage value) by the estimated useful life of the asset. Therefore, the correct choice is B, Depreciable cost / Estimated useful life. Option A, Initial cost / Estimated useful life, is incorrect as it does not take into account the salvage value of the asset. Option C, Depreciable cost × Estimated useful life, and Option D, Initial cost × Estimated useful life, are both incorrect as they do not divide by the estimated useful life to determine the annual depreciation amount.