Know the payment but not the rate? Work backward to the APR.
A loan rate calculator solves for the interest rate (APR) implied by a loan amount, monthly payment, and term, useful when you know the payment but not the rate you're being charged.
Loan quotes sometimes lead with the payment and bury the rate. Given the amount, payment, and term, there's exactly one interest rate that fits, and the calculator finds it with a numerical search. Knowing the true APR lets you compare an offer against others on equal footing.
A low monthly payment can hide a high rate stretched over a long term, so a payment that feels affordable may carry an expensive APR. If the payment is barely above the interest, the implied rate is high and little goes to principal. Always convert a 'payment' offer back to its rate before signing.
Given the amount, payment, and term, exactly one rate fits. The calculator solves for it numerically and shows the APR.
They should, and by law usually must, but 'payment-first' offers can obscure it. Converting back to the APR reveals the true cost.
If total payments don't exceed the loan, no positive rate fits, the payment wouldn't cover the principal.
See the exact formula and a worked example on our methodology page.