In my case, since I can’t tax depreciation of my card, the only purpose of depreciation is to extend the expense of depreciation among years for my personal interest. So, in this case, I do not want to estimate depreciation yearly. I prefer to wait until I sell or discard the car in order to attribute the depreciation expense to each year.
When I buy the car:
2020-01-01 buy car
assets:properties 1 CAR @@ 30000.00 EUR
assets:cash
If I want to track an estimation of the value of the CAR to estimate better my net worth:
P 2020-12-31 CAR 27000.00 EUR
P 2021-12-31 CAR 24000.00 EUR
P 2022-12-31 CAR 21000.00 EUR
P 2023-12-31 CAR 18000.00 EUR
But when i sell the car, I can exactly put the depreciation per year:
Price values (P directives) are my yearly depreciation estimation. For example, I buy a car for 30000 EUR and I estimate that ten years later it would value 6000 EUR so my price values drop at 2400 EUR per year during 10 years.
But this a personal estimation.
If I finally sell my car after 5 years per 20000 EUR, I lost 10000 EUR in 5 years so I actually had 2000 EUR depreciation per year during 5 years although my estimation was 2400 EUR.
And please take into account that this method is only valid for personal finances. Because anual books should reflect the estimated value of assets and previous annual books should not be modified in corporate finances. Depreciation is to reflect the current value of assets. If you understimate depreciation you will have a capital loss at selling and if you overstimate you will have capital gains at selling.
Since I am doing book keeping for personal finances, i can wait to set the depreciation per year until I know exactly what is the real depreciation and avoid the final capital gain/losses due to divergences between the estimation and the real depreciation.