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Calculators / Finance / Interest rate solver
Interest rate solver calculator
Solve the approximate annual rate implied by a principal, fixed payment and term.
On this page
Approximate annual interest rate6%
Total interest3,999.2
Calculator controls
How to calculate
Solve the approximate annual rate implied by a principal, fixed payment and term.
Find the monthly rate r where payment = principal × r ÷ [1 − (1+r)^−n], then annualize as 12r.
Worked example
Loan principal: 25000; Monthly payment: 483.32; Number of payments: 60.
Approximate annual interest rate: 6 %; Total interest: 3,999.2 .
Assumptions and limits
The solution assumes level end-of-month payments, no fees and a positive rate. Payment must be high enough to repay principal within the term.
Results are rounded for display; calculations use unrounded values. Read our calculation methodology.
Understanding the result
Solve the approximate annual rate implied by a principal, fixed payment and term. The displayed figures use the inputs and formula shown on this page.
When this tool is useful
Use the interest rate solver to compare a scenario, check an estimate, or verify a manual calculation.
Understanding your inputs
| Input | What to enter |
|---|---|
| Loan principal | Enter a number of at least 0.000001 and no more than 1000000000000. |
| Monthly payment | Enter a number of at least 0.000001 and no more than 1000000000000. |
| Number of payments | Enter a number of at least 1 and no more than 1200. |
Frequently asked questions
What should I check before using the interest rate solver result?
The solution assumes level end-of-month payments, no fees and a positive rate. Payment must be high enough to repay principal within the term.
Is this interest rate solver result exact?
It is exact for the stated mathematical model and entered values. Real-world results can differ when rates, timing, fees, definitions or measurement conditions differ.