Loan Interest Rate Finder
Know your loan amount, monthly payment, and term but not the rate? Find it instantly. Or calculate monthly payment or loan duration from the other two variables.
All calculations happen in your browser. No data is sent anywhere.
Find Interest Rate
Enter the loan amount, your monthly payment, and the loan term.
Find Monthly Payment
Find Loan Term
How It Works
Finding the Interest Rate
There is no algebraic formula to solve for the interest rate from payment, principal, and term — it requires numerical iteration. This calculator uses Newton–Raphson to converge on the monthly rate in typically fewer than 50 steps, with precision to 8 decimal places. The annual nominal rate is monthly rate × 12; APR (EAR) is (1 + monthly rate)^12 − 1.
The Amortizing Loan Formula
A standard loan uses equal monthly payments that cover interest and principal: PMT = PV × r × (1+r)^n / [(1+r)^n − 1]. Each month, interest accrues on the remaining balance, and the rest of the payment reduces the principal. Early payments are mostly interest; later payments are mostly principal. This calculator handles all three unknowns.
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Open calculator →FAQ
How do I find the interest rate on a loan?
Enter the loan amount, monthly payment, and number of months in the "Find Interest Rate" tab. The calculator uses Newton–Raphson iteration to find the monthly rate and converts it to annual nominal rate and APR.
What is the difference between nominal rate and APR?
The nominal annual rate = monthly rate × 12. APR (EAR) = (1 + monthly rate)^12 − 1, which accounts for monthly compounding. For example, a 12% nominal rate becomes a 12.68% APR. Lenders in many countries are required to disclose APR so borrowers can compare products fairly.
How is the monthly loan payment calculated?
PMT = PV × r × (1+r)^n / [(1+r)^n − 1], where PV is the principal, r is the monthly rate (annual ÷ 12), and n is months. For a $200,000 mortgage at 6% for 30 years: r = 0.005, n = 360, PMT ≈ $1,199.
Why does my payment seem too small?
If your monthly payment is less than the monthly interest accrued (Principal × monthly rate), the loan balance grows each month and never pays off. The "Find Loan Term" tab shows an error in this case. You need to increase your payment above the monthly interest amount.