Accumulated depreciation is the total depreciation taken on an asset over all years you’ve owned it. This includes depreciation claimed in prior years plus the current year amount, and it reduces the asset’s remaining value for tax purposes.
To determine this year’s accumulated depreciation, start with last year’s total depreciation (from Form 4562 or your depreciation schedule) and add any depreciation taken in earlier years. Review your prior-year Form 4562 and supporting asset worksheets to see the running total—this combined amount represents your accumulated depreciation to date.