Twice the straight-line rate, applied to book value
Double-declining balance is an accelerated US book method. The annual rate is 2 ÷ useful life. Each full year multiplies beginning book value by that rate, then the charge is capped so book value does not fall below salvage. Straight-line spreads cost minus salvage evenly. This page matches Excel DDB without switching to straight-line when that amount would be larger, and it does not load MACRS percentages or a half-year convention.
Year t expense = min(beginning book value × rate, beginning book value − salvage)
Book value = cost − accumulated depreciation
Example
A $10,000 machine with $1,000 salvage and a 5-year life uses a 40% rate. Year 1 depreciation is $4,000 and book value is $6,000. Year 2 is $2,400. By year 5 the cap leaves $296 so book value equals salvage. A $50,000 asset with $5,000 salvage and a 5-year life is $20,000 in year 1; year 5 is $1,480.
What this schedule leaves out
Useful life and the year to report must be whole numbers. Year 0 leaves book value equal to cost. Partial-year conventions, 150% declining balance, the optional switch to straight-line, Section 179, and IRS MACRS tables stay outside this full-year identity.