Interest Rate Calculator
Updated on 22 Oct 2026 · Checked by Aotob
Repaying $20,000 at $450 a month for 5 years means an interest rate of 12.5%.
You pay $7,000 in interest.
Interest rate
12.5%a year
Check this against the APR the lender quotes. If yours is higher, fees are being added to the loan.
Show the working
Solve 20,000 × r ÷ (1 − (1 + r)−60) = 450.00 for r
r = 1.042% a month = 12.504% a year
Payment at nearby rates
| Rate | Payment |
|---|---|
| 10.5% | 429.92 |
| 11.5% | 439.89 |
| 12.5% | 450.00 |
| 13.5% | 460.24 |
| 14.5% | 470.61 |
Questions people ask
Why work out the rate?
Dealers and some lenders quote only a monthly payment. Knowing the rate lets you compare it with other offers.
How is it worked out?
The rate is found by trial: the calculator tries rates until the standard loan payment formula gives your payment.
Is this the APR?
It is the rate that matches the payment. If you also paid fees up front, the APR calculator gives the true yearly cost.
Updated 22 Oct 2026Source: Standard financial maths (time value of money)Checked by AotobAssumes equal monthly payments. Not financial advice.Report an issue