Loan Calculators
Interest Rate Calculator
Work backwards from a known loan amount, payment and term to the interest rate the lender is actually charging.
Implied annual interest rate
3.2%
- Total repaid
- $19,200
- Total interest
- $1,200
How this calculator works
Solve P = M × (1 − (1 + r)^−n) ÷ r for r, then annualise
- P
- the amount borrowed
- M
- the monthly payment
- n
- the number of payments
Example calculation
Illustrative example — not advice
Worked example — the interest rate calculator as it loads, using the default figures below.
- 01Enter amount borrowed: $18,000.
- 02Enter monthly payment: $400.
- 03Enter term: 48 months.
- 04Read the implied annual interest rate from the results panel: 3.2%.
Implied annual interest rate: 3.2%. Total repaid: $19,200. Total interest: $1,200.
These figures come straight from the calculator above running on the values listed, so you can retype them and confirm every number yourself. Change any input and the results update immediately. Illustrative only — not a quote, offer or recommendation.
Important considerations
- If the payments total less than the amount borrowed, no positive rate exists.
- Fees inside the payment inflate the implied rate — that is closer to an APR.
Related calculators
- APR CalculatorThe true annualised cost of a loan once fees are included.
- Loan Payment CalculatorMonthly repayment, total interest and the effect of paying extra each month.
- Loan Interest CalculatorTotal interest cost across the life of a loan.
- Effective Interest Rate CalculatorEffective annual rate for any compounding frequency.
- Personal Loan CalculatorRepayments and total interest on an unsecured personal loan.
- Student Loan CalculatorStudent loan repayments, interest and payoff timing.
Terms used here
Frequently asked questions
Why would I need this?
Dealers and retailers often quote a payment and a term without a rate. This reveals what that arrangement actually costs.
Disclaimer
Legamoney calculators are educational tools. Results are estimates based on the figures you enter and do not constitute financial, tax or legal advice.
Last reviewed 2026-08-01