I don't use price to track depreciation of fixed assets. At the end of an accounting period (e.g. annually), I insert an adjusting entry to recognize the depreciation as an expense. There are several methods for figuring out the depreciation amount for a period, but straight-line depreciation is
(Purchase Cost - Salvage Value) / Useful Life. Salvage value is the amount you expect to recoup when you dispose of the asset, which can be 0 if you plan to use the asset until it's worthless, or an estimate of a fair value to get for selling it. For a business, the accounting principles for your locale will dictate rules on salvage value and useful life. But for personal accounting (where, at least in the U.S., you cannot use depreciation for personal assets), you can use whatever you want for those values. The transactions would look like:
2020-01-01 * "Car" "Purchase"
Assets:Bank:MyBank -20,000 EUR
Assets:Equipment:Vehicles 1 CAR.MAKEMODEL {20,000 EUR}
2020-12-31 * "Car" "Depreciation Expense"
Assets:Equipment:Vehicles
Expenses:AccumulatedDepreciation 2,000 EUR
2021-12-31 * "Car" "Depreciation Expense"
Assets:Equipment:Vehicles
Expenses:AccumulatedDepreciation 2,000 EUR
Note that this will store multiple commodities in the Assets:Equipment:Vehicles – you still have 1 CAR.MAKEMODEL, in addition to a contra-asset in EUR representing the depreciated value. Upon the sale (or other disposition) of the asset, you would debit the fixed asset (CAR.MAKEMODEL) and credit the entire amount of accumulated depreciation. That balances against the profit/loss of the sale of the car. E.g., sell the car 2 years later at 18,000 EUR for a profit of 2,000 EUR:
2022-01-01 * "Car" "Sale"
Assets:Equipment:Vehicles -1 CAR.MAKEMODEL {20,000 EUR} @ 18,000 EUR
Assets:Equipment:Vehicles 4,000 EUR
Assets:Bank:MyBank 18,000 EUR
Income:Equipment:Vehicles:PnL -2,000 EUR
I think this is preferable to using price directives, because the price of the car is actually the fair-market value for what you could get if you were to sell it at a point in time. The price could be less or greater than current depreciated value based on your useful life estimate.
- Robert