Introduction
If you know how much you borrowed, how long your loan lasts, and what you pay each month, this calculator will find your interest rate. It works backward from the numbers you already have to figure out the annual percentage rate hidden inside your loan. This is useful when a lender does not clearly show you the rate, or when you want to compare two loans side by side. Just type in your loan amount, the term in years and months, and your monthly payment. The calculator does the math instantly and shows you the implied interest rate, total interest paid, and a clear chart of how your balance drops over time.
How to Use Our Interest Rate Calculator
Enter your loan details below, and this calculator will find the annual interest rate on your loan based on the amount you borrowed, your loan term, and your monthly payment.
Loan Amount: Type the total amount of money you borrowed. This is the principal of your loan before any interest is added.
Loan Term (Years): Enter the number of full years you have to pay back the loan. If your loan is less than one year, leave this at zero and use the months field instead.
Loan Term (Months): Enter any extra months on top of the years. For example, a 3-year, 6-month loan would be 3 in years and 6 in months.
Monthly Payment: Type the fixed dollar amount you pay each month toward the loan.
Click Calculate to see your implied annual interest rate, total amount paid, and total interest paid. The tool also shows a chart of principal versus interest and a graph of your remaining balance over time. Click Reset to return all fields to their default values.
What Is an Interest Rate Calculator?
An interest rate calculator helps you find the annual interest rate on a loan when you already know the loan amount, the loan term, and the monthly payment. This is useful when a lender tells you your monthly payment but does not clearly state the interest rate. Instead of guessing, you can plug in your numbers and get the exact rate you are being charged.
How Interest Rates Work
When you borrow money, the lender charges you a fee for using their money. That fee is called interest. The interest rate is shown as a percentage of the loan amount per year. A higher rate means you pay more over the life of the loan. A lower rate means you pay less. Even a small difference in the rate can add up to hundreds or thousands of dollars over time.
What This Calculator Shows You
This tool solves for the implied annual interest rate based on your inputs. It also shows you the total amount you will pay, how much of that is interest, and how much is principal. The principal is the original amount you borrowed. The charts break down how your balance drops over time and how your total payment splits between principal and interest.
When to Use This Calculator
Use this calculator when you are comparing loan offers, checking a dealer's financing terms, or reviewing an existing loan. If you know three of the four values (loan amount, term, monthly payment, and interest rate), you can always find the missing one. This calculator finds the rate for you. If you want to compare the true cost including fees, our APR Calculator accounts for those extra charges.
Simple vs. Compound Interest
This calculator uses compound interest, which is how most real loans work. With compound interest, you pay interest on the remaining balance each month. As you pay down the balance, the interest portion of each payment gets smaller and the principal portion gets larger. This is called amortization. If you want to see how basic, non-compounding interest works instead, our Simple Interest Calculator handles that scenario.