How the Depreciation Calculator Works
The calculator works from three inputs — the asset cost, its salvage (residual) value and its useful life in years — plus a chosen method, and builds a year-by-year schedule of opening value, depreciation, accumulated depreciation and closing book value. The depreciable base is cost − salvage, and the asset is never written below salvage, so accumulated depreciation tops out at exactly the depreciable base. Five methods are supported. Straight-line charges (cost − salvage) ÷ useful life every year. Declining balance charges (factor ÷ life) × the opening book value, where the factor is selectable (1.25×, 1.5× or 2×). Double-declining balance is the 200% case (2 ÷ life × book value) and switches to straight-line on the remaining balance in the year that gives a larger deduction, so the asset reaches salvage exactly. Sum-of-years’-digits charges (remaining life ÷ sum-of-years) × depreciable base, where sum-of-years = n(n+1)/2. Units-of-production charges (cost − salvage) ÷ total units × the units produced each year, assuming constant usage by default. Every result comes from a pure function in a small, unit-tested engine, shown live with a pure-SVG book-value chart.
- Depreciable base = cost − salvage; book value never falls below salvage
- Straight-line = (cost − salvage) ÷ useful life, equal every year
- Declining balance rate = factor ÷ life, applied to opening book value
- Double-declining = 200% declining, switching to straight-line near the end
- Sum-of-years = n(n+1)/2; units-of-production charges by output
