# How do I calculate the depreciation value of a car?

$V = C - {\left(1 - r\right)}^{t}$
where $V$ is the value of the car after $t$ years, $C$ is the original cost and $r$ is the depreciation rate.
Example if the initial cost of the car is $10,000, the depreciation rate is 25% and the present value of the car is$4,000, we can calculate how old the car is.
4000=10000*(1-0.25)^t => 0,75^t = 0.4 => t*log0.75=log0.4 => t=log0.4/log0.7~~2.57 years