Calculate sum-of-years-digits accelerated depreciation with yearly expense breakdown and comparison to straight-line method.
The sum-of-years-digits method loads an asset's depreciation into its early years by multiplying the depreciable base by a shrinking fraction each year. This tool computes that schedule from cost, salvage value, and useful life, then lines it up year by year against straight-line, showing the expense difference in each year and the running book value. The surprise most users hit: the accelerated schedule and straight-line end at exactly the same total. The method only shifts when the expense is recognized, and the depreciable base is cost minus salvage, not the full cost.
A concrete input and expected output from the current implementation.
Input
Cost: $10,000 | Salvage value: $1,000 | Useful life: 5 years
Expected output
Depreciable base: $9,000. Sum of years digits: 15. Year 1: $3,000; Year 2: $2,400; Year 3: $1,800; Year 4: $1,200; Year 5: $600. Total depreciation: $9,000. Book value after year 5: $1,000 (salvage). Straight-line: $1,800 per year. Difference vs. straight-line: +$1,200, +$600, $0, -$600, -$1,200.
Each year's fraction is remaining life over 15 (5/15, 4/15, 3/15, 2/15, 1/15) applied to the $9,000 depreciable base. The fractions sum to 1, so total depreciation equals the base and book value ends exactly at salvage; against straight-line's flat $1,800, SYD is higher in years 1-2, equal in year 3, and lower afterward.
The denominator is the sum of the life's digits: for n years, 1 + 2 + ... + n = n(n+1)/2. Each year's fraction is the remaining life over that sum, so a 5-year asset takes 5/15, 4/15, 3/15, 2/15, then 1/15. Every fraction multiplies cost minus salvage, and because the fractions add to exactly 1, total depreciation always lands on the depreciable base.
Straight-line divides the depreciable base evenly across the life. The tool prints both schedules side by side with a per-year difference: SYD runs ahead in the early years, falls below straight-line around the middle of the life, and the differences sum to zero. Both methods finish with the same total expense and the same ending book value, so the comparison isolates timing rather than total cost.
Because the method is deliberately accelerated: the largest fraction applies in year one. For a 5-year asset that is 5/15 of the depreciable base versus 1/5 under straight-line. The trade-off is smaller deductions in later years, and the lifetime total is identical to straight-line, so the method changes timing, never the total amount recovered.
For U.S. federal tax, usually not. Business tangible property placed in service after 1986 is depreciated under MACRS, per IRS Publication 946, and sum-of-years-digits is not one of its methods. Use this tool for book schedules and internal analysis, and the MACRS tables for the tax return. State or foreign regimes can differ.
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