Most people sign a car loan, see a monthly payment, and never look at how the interest actually works. That's expensive, because the mechanics decide whether you pay $4,000 or $15,000 in interest on essentially the same car. The math is simpler than dealers make it sound, and once you see it, every lever — term, down payment, extra principal — becomes obvious.
Nearly all car loans today are simple-interest contracts. Interest accrues daily on your unpaid balance: your APR divided by 365, multiplied by the principal, times the days since your last payment. Each month, your payment first covers that accrued interest, and whatever is left knocks down the principal. Next month the interest slice is slightly smaller, because the balance is. That's amortization.
The important property is that interest never compounds — you're never charged interest on interest. That's what makes extra payments on a car loan so effective: every dollar of principal you retire early stops generating daily interest for the rest of the loan.
Lenders use the standard installment formula: payment = P × (r ÷ 12) ÷ (1 − (1 + r ÷ 12)−n), where P is the amount borrowed, r is the annual rate as a decimal, and n is the number of payments. The auto loan calculator runs this with your exact numbers; the pattern to internalize is the front-loading:
Take a $30,000 loan at 6.39% for 60 months. The payment is $585.44. The first month's interest is $30,000 × 0.0639 ÷ 12 = $159.75, so only $425.69 of your payment touches principal. By the final year the split has flipped, and almost the whole payment is principal. Early in the loan you're renting money; late in the loan you're paying it back.
According to Experian's State of the Automotive Finance Market data for Q1 2026, the average new-car APR was 6.39% and the average used-car APR was 11.43%. Where you sit in that range is mostly your credit tier:
| Credit tier | Score range | New APR | Used APR | Avg new payment |
|---|---|---|---|---|
| Super prime | 781+ | 4.55% | 6.30% | $753 |
| Prime | 661–780 | 6.23% | 8.77% | $774 |
| Near prime | 601–660 | 9.67% | 14.03% | $811 |
| Subprime | 501–600 | 13.44% | 19.42% | $792 |
| Deep subprime | 300–500 | 16.01% | 21.77% | $763 |
Read the gap between the top and bottom rows twice: a deep-subprime borrower pays more than three times the super-prime rate on a new car, and more than double the average on a used one. The average new-car loan is now $43,925 with a payment of $770 a month, which is why the rate you qualify for moves the total cost by five figures.
Rate and term multiply each other. The same $40,000 borrowed at the 6.39% average new-car rate, across common terms:
| Term | Monthly payment | Total interest |
|---|---|---|
| 36 months | $1,224 | $4,063 |
| 48 months | $947 | $5,435 |
| 60 months | $781 | $6,835 |
| 72 months | $670 | $8,262 |
| 84 months | $592 | $9,715 |
Now the same loan at the 13.44% subprime new-car average: $919 a month over 60 months with $15,149 of interest, or $812 over 72 months with $18,484. Stretch to 84 months and it's $21,932 — you'd pay more than half the car's price again in interest. This is the arithmetic behind the old advice to buy a cheaper car or a bigger down payment instead of a longer loan: term length is where subprime pricing does its damage.
On a car loan they're often the same number, but not always. The interest rate is the pure cost of borrowing; the APR folds in mandatory fees the lender charges, expressed as a yearly rate. If two quotes show the same rate but different APRs, the higher-APR loan has more fees buried in it. Comparing APR to APR — and asking the lender to itemize the fees — is the only apples-to-apples way to judge quotes. Also confirm which number a dealer is quoting you: "buy rate" is what the lender approved; dealers in most states can mark it up, and the markup is negotiable.
A small minority of loans — mostly older contracts and some subprime paper — use precomputed interest: the full interest for the term is calculated upfront and baked into your balance. Paying early saves you little or nothing, and some of these contracts carry prepayment penalties on top. The worst variant, the rule of 78s, front-loads even more of the interest into the early months.
It's a dying structure, and several states bar it, but the defense takes one minute: read the prepayment section of the contract before signing. If the words "precomputed" or "rebate of unearned interest" appear, ask for a simple-interest contract instead, or a different lender.
Enter price, down payment, rate, and term — the calculator returns the payment, total interest, and total cost so you can compare terms side by side before you sit down at the dealership.
Auto Loan Calculator →Car loan interest is simple interest that accrues daily on what you owe: payment covers the accrued interest first, principal second, and the balance tips toward principal as the loan ages. The average borrower pays 6.39% on a new car and 11.43% on a used one, with subprime tiers at 13% to 22%. Term is the quiet multiplier — stretching $40,000 from 60 to 84 months costs nearly $2,900 more at average rates. Price the loan before the car with the auto loan calculator, check the payment against your budget with the car payment calculator, and revisit the rate later with the auto refinance calculator.
Most car loans are simple-interest contracts: interest accrues daily on your unpaid principal at your APR divided by 365, and each payment covers the accrued interest first with the remainder reducing principal. There is no interest on interest, so paying early or extra always saves you money on a simple-interest loan.
Super prime territory, roughly 781 and above, where the average new-car APR is 4.55% and the average used-car APR is 6.30% as of Q1 2026. Prime borrowers (661-780) average 6.23% new and 8.77% used. Below 660 the pricing climbs fast: 9.67% new for near-prime, 13.44% for subprime, and 16.01% for deep subprime.
Yes, and for an unglamorous reason. Biweekly payments produce 26 half-payments a year, which is 13 full payments instead of 12. On a simple-interest loan the extra payment goes straight to principal, which shortens the loan and cuts total interest. You can get the identical effect by adding one-twelfth of a payment to each monthly check.
Usually, yes. Most auto loans today are simple-interest contracts with no prepayment penalty, so extra principal payments save interest directly. Check your contract before assuming: a small share of older or subprime contracts carry precomputed interest or rule-of-78s terms, where paying early saves you little or nothing.
Used vehicles serve as collateral worth less and falling, so lenders price more risk into the loan: the average used-car APR was 11.43% in Q1 2026 versus 6.39% for new. Older cars also carry higher default rates in lender data. Manufacturer-subsidized new-car rates, sometimes 0.9% to 4.9%, widen the gap further.