The auto loan formula: a 72-month term at 6.8% APR on $35,000 adds nearly $8,000 in interest vs a 48-month loan. How down payment and rate change the total.
An auto loan is an amortizing installment loan, which means each fixed monthly payment covers the interest accrued that month and applies the remainder to the principal. As the principal shrinks, the interest portion of each payment shrinks with it, and more of the payment goes toward principal. The math is identical to a mortgage: the same standard amortization formula governs both.
According to Experian, the average amount financed on a new vehicle in the United States reached approximately $41,000 in 2025, with an average APR of about 6.8% and an average term of roughly 68 months. For used vehicles, the average APR was substantially higher at approximately 11.9%, reflecting the greater default risk and shorter useful life of older collateral. These figures come from the Experian State of the Automotive Finance Market report, published quarterly.
M = P × [ i(1 + i)^n ] / [ (1 + i)^n − 1 ]
| Variable | Meaning |
|---|---|
| M | Monthly payment (principal and interest) |
| P | Principal = vehicle price − down payment − trade-in |
| i | Monthly interest rate = annual APR ÷ 12 |
| n | Total number of monthly payments |
Suppose you finance $35,000 at a 6.8% APR over 72 months. The monthly rate i = 0.068 ÷ 12 = 0.005667, and n = 72. Plugging these into the formula gives a monthly payment of approximately $593.55.
Over the full 72 months you pay $593.55 × 72 = $42,736, of which $7,736 is interest. In the first month, the interest charge is $35,000 × 0.005667 = $198.33, meaning only $395.22 of the $593.55 payment reduces the principal. By month 48, the balance has declined enough that the interest charge is roughly $78 and over $515 of the payment goes to principal. This front-loaded interest structure is the defining feature of amortization and is the reason early extra payments save far more than late ones.
You can verify any of these figures with the Metriova auto loan calculator, which runs the identical formula in your browser.
Extending the loan term lowers the monthly payment but raises total interest, because the principal balance remains outstanding for longer and accrues more interest. The Consumer Financial Protection Bureau (CFPB) warns that longer terms increase the risk of negative equity, where the borrower owes more than the vehicle is worth. Using the same $35,000 balance at 6.8% APR, compare four common terms:
| Term | Monthly Payment — Total Interest |
|---|---|
| 48 months | $835 — $5,080 |
| 60 months | $690 — $6,400 |
| 72 months | $594 — $7,736 |
| 84 months | $525 — $9,108 |
Moving from 60 to 84 months cuts the monthly payment by $165 but adds $2,708 in total interest. The CFPB notes that loans extending beyond 72 months now account for roughly 40% of new-vehicle originations, a record high. The risk is that vehicles depreciate faster than the long-term loan balance declines: Edmunds reports the average new vehicle loses about 20% of its value in the first year and over 40% after five years, so an 84-month loan can leave the borrower underwater for several years.
Interest rates differ sharply between new and used vehicles because lenders price in the risk of default and the residual value of the collateral. The Experian State of the Automotive Finance Market report shows the following average rates and loan amounts for 2025:
| Vehicle Type | Avg APR — Avg Amount Financed |
|---|---|
| New vehicle | ~6.8% — ~$41,000 |
| Used vehicle | ~11.9% — ~$26,000 |
| Average credit score (new) | ~750 |
| Average credit score (used) | ~680 |
A borrower with a credit score above 780 typically qualifies for the lowest advertised rates, often 2-4 percentage points below the average, while subprime borrowers (score below 600) may face APRs above 18%. The Federal Reserve publishes the average auto loan finance rate in its G.19 Consumer Credit release. Because the APR compounds over the full term, a 5 percentage point difference on a $30,000 loan over 72 months changes total interest from roughly $5,600 to over $11,800 — more than double.
Every dollar paid upfront reduces the principal that accrues interest. On a $40,000 vehicle financed at 6.8% APR for 72 months, compare two down payment levels:
A trade-in works the same way: the dealer credit reduces the financed principal. The CFPB recommends negotiating the vehicle price separately from the trade-in and financing to avoid having the trade-in value rolled into a higher loan amount. When the down payment is below 20%, lenders may require Guaranteed Asset Protection (GAP) insurance, which covers the difference between the loan balance and the actual cash value if the vehicle is totaled. GAP insurance typically costs $200-$700 as a one-time add-on to the loan.
Several concrete steps reduce the total cost of an auto loan:
Sources: Experian State of the Automotive Finance Market, Consumer Financial Protection Bureau (auto loan guidance and total cost of credit), Federal Reserve G.19 Consumer Credit release, and Edmunds vehicle depreciation data. Use the Metriova auto loan calculator to model your own scenario with any price, APR, term, and down payment. This content is educational and is not financial advice.
Auto Loan Calculator — Trade-In & Monthly Payment
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