On a $28,000, 60-month auto loan, raising the APR from 6.00% to 6.75% raises total interest paid over the loan from $4,479.11 to $5,068.21, a $589.10 difference, even though the monthly payment itself rises by only $9.82, from $541.32 to $551.14.
auto loan apr vs total interest cost: the measured relationship
The annual percentage rate (APR) is a standardized, annualized measure of a loan's cost that federal Truth in Lending disclosures require lenders to state; total interest cost is the actual dollar sum of every interest charge paid across the loan's full amortization schedule, which depends on both the APR and the number of payments. APR lets a borrower compare loans of the same term on a standardized annual basis; total interest cost is a term-dependent dollar figure, so a loan with a lower APR but a longer term can still produce more total interest than a loan with a higher APR and a shorter term, as the second case below shows.
| Amount financed | $28,000 |
|---|---|
| Term | 60 months |
| 6.00% APR: payment / total interest | $541.32 / $4,479.11 |
| 6.75% APR: payment / total interest | $551.14 / $5,068.21 |
| Interest difference | $589.10 |
auto loan apr vs total interest cost: a worked dollar case
Financing $28,000 for 60 months at a 6.00% APR gives a monthly rate of 0.06 divided by 12, or 0.005. The standard payment formula, principal times the monthly rate divided by one minus one plus the monthly rate raised to the negative number of payments, gives a monthly payment of $541.3184, rounded to $541.32. Over 60 payments, total paid is $32,479.11, so total interest is $32,479.11 minus $28,000, or $4,479.11. Raising the APR to 6.75% on the identical $28,000 and 60-month term changes the monthly rate to 0.005625, the payment to $551.1369, rounded to $551.14, total paid to $33,068.21, and total interest to $5,068.21 -- a $589.10 increase in interest cost from a 0.75-percentage-point APR difference.
auto loan apr vs total interest cost: calculation method
Monthly payment equals principal times the monthly rate divided by one minus one plus the monthly rate raised to the negative power of the payment count, where the monthly rate is the APR divided by 12. Total paid equals the monthly payment times the number of payments, and total interest equals total paid minus the amount financed. Recompute the monthly rate every time the APR, principal, or term changes; none of the three inputs can be assumed constant across two loan offers.
autoloanaprvstot related calculations: auto loan calculator; APR calculator; APR versus APY guide.
A second case: the same 6.00% APR over a shorter term
The same $28,000 principal at the same 6.00% APR produces a different total-interest figure once the term changes from 60 months to 36 months. At 36 months the monthly payment rises to $851.8142, rounded to $851.81, because the same balance is repaid faster; total paid over 36 payments is $30,665.31, so total interest is $2,665.31 -- $1,813.80 less than the $4,479.11 paid at 60 months on the identical rate and principal. The APR did not move; only the number of payments over which the balance amortizes changed, and that alone reshaped both the monthly payment and the total interest cost.
Three amortization schedules side by side
| Loan | Term | Payment | Total interest |
|---|---|---|---|
| $28,000 at 6.00% | 60 months | $541.32 | $4,479.11 |
| $28,000 at 6.00% | 36 months | $851.81 | $2,665.31 |
| $28,000 at 6.75% | 60 months | $551.14 | $5,068.21 |
Reading the table by column shows two separate levers: moving down the APR column at a fixed 60-month term adds $589.10 of interest, while moving down the term column at a fixed 6.00% APR removes $1,813.80 of interest -- the term change has more than three times the effect of the 0.75-point rate change in this example, which is why total interest cannot be judged from the APR figure alone.
Checking the 60-month, 6.00% result by summing the amortization schedule
The formula-based total interest for the $28,000, 60-month, 6.00% APR loan, $4,479.11, can be checked by simulating the amortization schedule payment by payment rather than trusting the closed-form formula alone. Starting from a $28,000 balance, each month's interest equals the remaining balance times 0.005, and each month's principal equals the $541.32 payment minus that interest; carrying this forward for 60 months and summing the 60 interest charges gives $4,479.1066, which rounds to the same $4,479.11 the formula produced, while the simulated balance after the 60th payment lands at exactly $0.00. A simulation that leaves a nonzero balance after the stated number of payments, positive or negative, signals a rate, rounding, or payment-count error rather than a genuine second answer.
The dispute this guide resolves: does a lower monthly payment mean a cheaper loan?
A monthly payment that looks lower is often read as the cheaper loan, but the 36-month loan in this guide's second case, $851.81 a month, carries a higher payment and a lower total interest cost, $2,665.31, than the 60-month loan's $541.32 payment and $4,479.11 of interest on the identical $28,000 principal and 6.00% APR. The payment figure by itself answers a cash-flow question, how much leaves the account each month, not a total-cost question, how much interest accrues before the balance reaches zero; a longer term lowers the payment specifically by extending the number of months interest is charged on a still-outstanding balance, which is the mechanism that raises the total-interest figure even when the APR itself never changes.
What a 0% APR promotion changes about this comparison
A manufacturer's 0% APR promotion removes the interest-rate variable from this guide's comparison entirely: at a 0.0000 monthly rate, the payment formula simplifies to principal divided by the number of payments, so a $28,000 loan over 60 months would carry a flat $466.67 payment with $0.00 of total interest. Promotional 0% offers are typically restricted to a shorter list of trims, require a larger down payment, or exclude a cash rebate that a standard-rate loan could apply instead, so the true cost comparison is not simply 0% against 6.00%; it is the 0% loan's forgone rebate, if any, against the standard-rate loan's total interest, $4,479.11 in the base case here, minus whatever rebate that loan does receive.
Common mistakes in Auto loan APR vs. total interest cost: how much does 0.75 points really add?
Do not compare two loan offers by monthly payment alone without also checking the term, since a lower payment can come from a longer term that adds interest cost; do not treat a dealer's 'buy rate' as identical to the APR on the contract, since dealer markup can raise the APR above the rate the lender quoted the dealer; and do not assume a rolled-in fee, extended warranty, or GAP insurance premium is excluded from the amount financed just because it is excluded from the interest-rate quote.
Where this calculation stops
This is principal-and-interest math on a level-payment schedule with no down payment, trade-in, sales tax, title fee, or insurance included, and it assumes the lender applies the monthly rate to the declining balance in the standard actuarial way. A specific lender's daily-interest or per-diem method at the first payment, an odd first-payment period, a prepayment penalty, or a co-signed loan's terms can each shift the actual total interest away from this simplified schedule.
auto loan apr vs total interest cost: source check
The Consumer Financial Protection Bureau explains that APR is a broader measure of borrowing cost than the interest rate alone because it can include certain fees, and that comparing the APR figure on a Truth in Lending disclosure is the standard way to compare loan offers. Read the named source. The autoloanaprvstot record should be reconciled to the disclosure, statement, tax bill, or agreement that governs that exact transaction.
auto loan apr vs total interest cost: using the output
The autoloanaprvstot output keeps each input's named unit and date adjacent to the result. Update the autoloanaprvstot scenario when its rate, balance, payment, or property value changes.