Start with three buckets
A lower monthly payment does not always mean a cheaper car. A longer loan can lower the payment while adding interest and keeping you in debt after the five-year comparison period.
1. Enter the deal, not the advertisement
Use the vehicle's negotiated price before your down payment. Add the sales-tax rate and the title, documentation and registration fees you expect to pay. For the loan, use the annual percentage rate you are actually offered—not the best rate in an ad.
Down payments change cash flow, not depreciation. Putting more down can reduce the monthly payment and interest, but the vehicle still loses value from the same purchase price.
2. Estimate the costs that repeat
- Insurance: use a quote for the exact model when possible. Your current premium may not transfer to a newer or more expensive car.
- Fuel: combine your annual mileage, expected miles per gallon and a realistic local fuel price.
- Maintenance: include routine service, tires and an allowance for wear. Older cars may need a larger repair cushion.
3. Treat resale value carefully
Depreciation is often the largest ownership cost, even though it never appears as a monthly bill. Use a conservative estimate of what the vehicle may be worth after five years. If two cars cost the same today, the one that retains more value can be meaningfully cheaper to own.
Keep mileage and insurance constant while comparing vehicles. Then test a higher fuel price, a lower resale value or a less favorable APR to see whether the decision still works.
What this estimate leaves out
The calculator does not include parking, tolls, annual property taxes, registration renewals, unexpected repairs, tax credits or the investment return you might have earned on your down payment. Add those separately when they are important to your decision.