Free tool · for car buyers
True Monthly Cost of a Car Estimator
The payment a salesperson quotes you is one line out of eight. It leaves out fuel, insurance, registration and taxes, servicing, tires — and the cost that is usually the largest of all, depreciation, which nobody ever invoices you for. This free estimator adds all eight lines for one car and returns the true monthly cost and the cost per mile, so you can see what the car actually takes from you rather than what leaves your account. It opens pre-filled with a worked example, so the shape of the answer is visible before you type anything.
Take it with you — free, no signup
Direct download. No email, no account — just the file.
What it does
- Adds up all eight monthly lines of owning a car — depreciation, financing cost, fuel, insurance, registration, servicing, tires and the standing costs you forget.
- Compounds depreciation on what the car is still worth, so it can never write off more than the car cost.
- Prices tires as a few cents on every mile from your own set cost and tire life, instead of leaving them as a surprise every few years.
- Returns the cost per mile — the only figure on which a car you drive gently and one you drive hard can be honestly compared.
- Sets the true monthly cost against the payment you were quoted, and explains plainly why those two are not the same kind of number.
- Opens pre-filled with a complete worked example you overwrite with the real car's numbers.
Related reading
Own it, don't rent it
Comparing two cars — and want to know where the answer flips?
This free tool prices one car with one flat depreciation rate. The full workbook reads each car's value off a per-year resale curve for five vehicle classes, anchored on iSeeCars' published analysis of more than 950,000 five-year-old vehicles — and works back to what a used car cost new, so buying at eight years old is computed rather than assumed. It amortizes a lease as a lease (money factor read as a rate, residual, acquisition and disposition fees, and mileage overage charged from the miles you really drive), escalates servicing by the car's age band and segment, and puts three cars side by side. Then it solves for the two things nothing else answers: the annual mileage, and the holding length, at which the cheapest car changes. Eleven connected tabs (Excel, Google Sheets or LibreOffice), five guides, and printable sheets for the dealership.
A one-time purchase you keep and reuse on the next car, and the one after that. No subscription, no lead form, and it works offline.
A financial planning aid, not licensed financial, tax or legal advice, and not a valuation or an appraisal. Every figure that ships in the file is an illustrative example for a car that does not exist — prices, interest rates, insurance, fuel and resale values vary enormously by market and change constantly. Confirm what matters with the dealer, your insurer and your own research. Free to use; please don't resell or redistribute.