How this instrument works
A car's value here is modeled as declining-balance depreciation: each year strips a fixed percentage off whatever the car is worth at the start of that year, not off the original sticker price. That is the same shape as compound interest running backward, and it is the model a private seller, a shopper comparing trade-in offers, or someone checking a loan payoff against resale value reaches for, because used-car prices genuinely fall faster early in a car's life than a flat, equal-dollar schedule would predict.
The mechanics matter because a constant rate does not mean a constant dollar loss. A car depreciating at 15% a year sheds a bigger dollar amount in year one, when the balance is still close to the purchase price, than in year five, when the balance has already shrunk several times over — the same percentage applied to a smaller number is a smaller number. This is the detail people confuse with straight-line depreciation, the method used for equipment and buildings, where every year loses an identical dollar amount by design.
The rate itself is an assumption you supply, not a guaranteed curve. Real depreciation varies by make, trim, mileage, accident history, and the used-car market's mood in a given year — a popular compact might hold value near 12% a year while a luxury sedan with costly upkeep can lose 20% or more, and the twelve months after a new-car purchase are typically the steepest stretch of all. This sheet holds the rate flat across every year owned; it does not know your specific vehicle's condition, and it says nothing about what a dealer will actually offer against it.
- Enter Purchase price, $ — what the car cost new, or what you paid for it.
- Set Annual depreciation rate, % to the yearly percentage you expect the car to lose.
- Give Years owned — how long you have held, or plan to hold, the car.
- Read Estimated value today for the declining-balance result after that span.
Worked example — a $30,000 car after five years
Set Purchase price, $ to 30000, Annual depreciation rate, % to 15, and Years owned to 5. Each year multiplies the prior balance by 0.85: $30,000 becomes $25,500 after year one, $21,675 after year two, $18,423.75 after year three, $15,660.19 after year four, and $13,311.16 after year five — the Estimated value today this sheet returns.
Notice the shrinking dollar amounts: the car loses $4,500 in year one but only about $2,349 in year five, even though the percentage never changes. A straight-line model splitting the same total $16,688.84 loss evenly across five years would charge $3,337.77 a year regardless — lighter in year one and heavier in year five than the declining-balance curve above actually shows.
Questions
Why does the car lose more value in year one than in year five?
Because declining-balance depreciation applies the percentage to whatever the car is worth right now, not to the original price. In year one that base is the full $30,000, so 15% is $4,500; by year five the base has already shrunk to about $15,660, so the same 15% is only about $2,349. The rate stays constant — the dollar loss does not.
How is this different from straight-line depreciation?
Straight-line depreciation, used for equipment and buildings, subtracts the same dollar amount every year, on the assumption of even wear over a fixed useful life. Declining-balance depreciation, used here, subtracts a fixed percentage of the remaining balance each year, so the dollar loss is largest early and tapers off — a better match for how cars actually lose value when new.
Where should the annual depreciation rate come from?
There is no single correct number — it is the assumption you are testing. Many mainstream cars settle near 15% to 20% a year on a declining balance; a $40,000 new car losing 20% in its first year alone would be worth $32,000 after twelve months, often called the 'drives off the lot' hit. Check recent private-sale or trade-in listings for your make, model, trim, and mileage to pick a fitting rate.
Will a dealer offer exactly what this calculator shows?
No. A trade-in or dealer offer also weighs mileage, condition, accident history, remaining warranty, and how much that dealer wants your specific model on the lot that week, then subtracts reconditioning cost and margin. This sheet gives a baseline curve built from one price and one rate; treat any real offer as a data point to compare against it, not the other way round.
I still owe money on an auto loan — does this tell me if I'm underwater?
It gives you half the comparison. Estimated value today is the asset side; you still need the loan's current payoff balance, which comes from an amortization schedule, not this sheet. If the payoff balance is higher than the value shown here, the loan is underwater — the car is worth less than what is still owed against it.
Does the depreciation rate stay the same every year in reality?
Rarely — real curves usually front-load the loss even more than one constant rate implies, with a sharp drop in year one that gradually flattens afterward. This sheet applies a single rate to every year for simplicity and transparent arithmetic; approximate a steeper early drop by running the numbers twice, using the year-one or year-two result as a fresh purchase price for the remaining years.
References
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.