Depreciation is the cost you feel when a car is worth less at resale than it was at purchase. It is not a monthly bill in the same way as fuel, but ignoring it can make an expensive car look cheaper than it really is to own.
The relationship behind the number
Future value = current value × (1 − annual depreciation rate)^years.
Numbers on a real vehicle
A $30,000 vehicle depreciating at an assumed 15% each year becomes $30,000 × 0.85^5 = about $13,311 after five years. The loss is $16,689. This is a planning model, not a resale promise; the first year may fall faster and a popular used model may lose value more slowly.
Before you compare two results
Mileage, service history, accident records, colour, specification, season and local supply all affect the actual price. Compare expected resale values for the same ownership period and mileage rather than applying one universal rate to every model. Dealer trade-in and private-sale prices are different too.
Where estimates commonly go wrong
Straight-line depreciation subtracts the same dollar amount each year; percentage depreciation compounds. Neither model captures a sudden market change, warranty expiry or a costly accident. Keep the model labelled as an estimate.
Keep the numbers useful over time
Conditions change. Fuel prices move, tyres wear, a battery loses usable energy in cold weather, and a vehicle’s mileage changes its resale value. Date your estimate and note the market or unit standard it uses. A dated, explainable estimate is more useful than a highly precise number with no trail back to its assumptions.
For comparisons, change one variable at a time. That reveals what is actually driving the result and avoids the false confidence that comes from changing distance, price and efficiency together.
A small habit that improves every estimate
Use a notebook or phone note with four columns: input, number, unit and source. It takes longer than typing three figures from memory, but it makes later corrections straightforward. You can replace a fuel price without accidentally replacing the MPG standard, or update an odometer reading without losing the earlier baseline.
For comparisons, keep the method fixed. Compare two cars with the same route, passengers, price date and ownership period. That is more informative than collecting impressive-looking figures from different adverts and hoping the labels line up.
Use a second scenario, not a second guess
Once the first answer is on screen, change one assumption that could realistically move. For a journey that might mean adding a detour; for a tyre calculation it may mean comparing an approved alternative; for finance it may mean a shorter term. Keeping every other input unchanged tells you how much that single choice matters. Write down the result and the assumption beside it.
This is also a useful way to spot implausible inputs. If doubling a distance barely changes a fuel bill, something is wrong. If a small tyre-profile change produces an enormous diameter difference, check the rim conversion and percentage calculation. A quick sense check often catches a typo before it becomes an expensive decision.
One detail worth carrying forward
A resale estimate is stronger when it uses local adverts or recent completed sales for the same age and mileage. Asking prices are not achieved prices, so leave room for negotiation and preparation costs. Service records and honest condition notes make the estimate more defensible than a generic annual percentage.
Pair the depreciation estimate with the ownership-cost calculator to see both cash expenses and value loss. For official specifications, safety limits and contract terms, use the responsible manufacturer, professional or lender document as the final authority.
Questions drivers often ask
Is depreciation higher in the first year?
Often, especially for a new car, but the pattern varies by brand, demand, incentives and market conditions.
Does mileage reduce resale value?
Usually higher mileage narrows the buyer pool, but condition and documented servicing also matter.
How can I reduce depreciation cost?
Choosing a model with steady demand, keeping records and avoiding unnecessary modifications can help, but no method guarantees a resale price.
Updated September 10, 2026