💰 直線折舊計算機（附不足整年折舊明細表）

Straight-line depreciation spreads the cost of a fixed asset evenly over its useful life. It is the simplest and most widely used depreciation method in accounting. The annual expense equals the depreciable base (cost minus salvage value) divided by the number of years of useful life, exactly matching Microsoft Excel's =SLN(cost, salvage, life) function. This calculator goes further by prorating the first (and trailing) fiscal year so the schedule reflects exactly when the asset was placed in service.

Enter the asset cost, its estimated salvage value, and the useful life in years. Select the month and year the asset was placed in service, then choose your fiscal (tax) year start month. Pick a depreciation convention — full-month, mid-month, mid-quarter, or half-year — to control how much of the placement period is taken. Toggle "Round to Dollars" for whole-dollar amounts and choose "Full Schedule" to see a year-by-year breakdown of expense, accumulated depreciation, and ending book value.

The annual amount is

The monthly amount is that divided by 12. Because an asset rarely starts at the beginning of a fiscal year, the first year receives only a fraction: first-year months ÷ 12. The leftover fraction carries into one extra trailing year so the totals always sum to Cost - Salvage. Conventions adjust the placement period: mid-month gives half a month, mid-quarter places the asset at the quarter midpoint, and half-year always takes six months in the first year.

Cost 10,000, salvage1,000, life 5 years, placed in service March 2020, Jan–Dec fiscal year, full-month convention. Depreciable base = 9,000; annual depreciation =

monthly =150. March is the 3rd fiscal month, so 13 − 3 = 10 months of depreciation in 2020: Years 2021–2024 each take 1,800, and the trailing year 2025 takes the remaining300. The expenses sum to exactly 9,000, leaving a final book value of1,000 (the salvage).