Double Declining Balance Calculator

Because depreciation compounds through the loop: each year's deduction is applied to whatever book value survived the previous years, so later years show a smaller deduction than earlier ones -- at the default 20% DDB rate, moving from year 1 to year 2 cuts the current-year deduction from $10,000 to $8,000, roughly a 20% drop, and book value falls by a similar share. Once the selected year passes useful life, the loop stops adding deductions entirely and current-year depreciation drops to zero (line 21-23). Asset cost has its own effect on both figures: a 10% change in cost shifts the deduction and book value by about 10% at any year, since both scale linearly with cost -- a different kind of change than a one-year step in the selected year, so the two aren't directly comparable as multiples of each other.

In year 1 specifically, yes, in opposite directions. Year 1 depreciation reduces to cost * (2 / usefulLife), so a 10% increase in cost raises it by about 10%, and a 10% increase in useful life lowers it by almost exactly the same amount -- the two inputs have a genuinely tied effect on the first year's deduction, not one outweighing the other.

Only when depreciation would otherwise carry book value below it. The engine caps each year's deduction at max(0, bookValue - salvageValue) (line 16), so at the default $50,000 cost, $5,000 salvage, and 10-year life, the declining-balance amount never gets close enough to the salvage floor to be capped -- salvage value sits inert until you push useful life short enough, or salvage value high enough, that the floor starts binding.

DDB Rate is the fixed percentage applied to book value every year, equal to 2 / usefulLife (200% of the straight-line rate, hence "double"). It depends on useful life alone -- asset cost, salvage value, and which year you're viewing never change it, since it's a rate, not a dollar amount, and this engine keeps that rate constant across every year of the schedule.