Loan interest rate calculator
When a lender gives you the payment and term without a clear rate, this tool finds the rate that matches the numbers.
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Processing and privacy: The result is calculated inside your browser and your data is not sent to any server.
How to use it
- Enter loan amount, monthly payment and number of payments.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
We solve numerically for the monthly rate x where P = payment × (1 − (1 + x)^−n) ÷ x. Annual rate = x × 12, effective annual rate = (1 + x)^12 − 1.
Example
Inputs: Loan amount = 100,000, Monthly payment = 599.55, Number of payments = 360 months. Result: Annual interest rate: 6%; Effective annual rate: 6.168%; Total interest: 115,838.00.
Limits and caveats
- Assumes equal monthly payments with no fees or balloon.
- If there are upfront fees, enter the net amount received to get a rate that includes them.
Questions about this tool
How is the rate found without a formula?
There is no closed-form formula, so the tool tries rates and narrows the range until the payment matches closely.
Why do I get 5.9999 instead of 6?
The payment you entered is rounded to cents, and that tiny gap shows up as a tiny gap in the rate.
What is the difference between the annual and effective rates?
The annual rate is the monthly rate × 12; the effective rate adds monthly compounding over the year.