Loan Calculator
Compute monthly payment and total interest for a fixed-rate loan.
Use one currency throughout. Results are in the same currency as your inputs.
Payment summary
— estimated monthly payment
How this loan calculator works
Personal loans, auto loans, and many installment products use the same math as a fixed-rate mortgage: a constant monthly payment that clears principal and interest by the end of the term. Enter the amount financed, the APR as an annual percent, and the length of the loan in years. The tool returns an estimated monthly payment and total interest over the life of the loan.
When to use it
Use this calculator when you have (or expect) a fixed APR and a set number of monthly payments — for example, comparing a 4-year versus 5-year auto loan, or seeing how a lower rate changes the monthly cost of a personal loan. It is less suitable for credit cards or revolving lines where the balance changes every month; use the debt payoff calculator for those.
Formula
Monthly payment follows standard amortization: with principal P, monthly rate r, and n months, payment = P × [r(1+r)n] ÷ [(1+r)n − 1]. Total interest is (payment × n) − P.
Worked example (dollars)
A $15,000 loan at 9% APR for 4 years has 48 payments. The estimated monthly payment is roughly $373, and total interest over the term is a few thousand dollars depending on rounding. Lowering the rate or shortening the term reduces total interest; lengthening the term usually lowers the monthly payment but raises interest paid.
Illustrative UK / Europe example (£)
Illustrative planning example only — not a loan offer or regulated advice. Enter the £ amounts below in the form to reproduce the comparison.
Compare a personal loan of £8,000 at 7.9% for 3 years versus the same amount over 5 years. The longer term lowers the monthly payment but increases total interest. A car finance sketch of £12,000 at 6.5% for 4 years uses the same amortization math — change only principal, rate, and term to stress-test quotes.
| Term | Months | What changes |
|---|---|---|
| 3 years | 36 | Higher monthly payment; lower total interest |
| 5 years | 60 | Lower monthly payment; higher total interest |
How to use it
- Enter the principal (amount you will borrow or still owe), in the currency of the loan.
- Enter the annual interest rate as a percent.
- Enter the term in years (decimals are allowed if your loan is quoted that way).
- Compare the monthly payment and total interest across a few realistic rate and term combinations.
Decision checklist before you sign
- Payment vs total interest — A longer term can make the monthly number feel affordable while raising lifetime interest. Change only the term and compare both outputs.
- Fees paid in cash vs financed — Origination or arrangement fees financed into the principal raise the amount amortized. Model the financed amount here, then add cash fees outside the calculator.
- Prepayment — If you expect to pay the loan off early, a slightly higher rate with no prepayment penalty can beat a “cheap” rate that locks you in. This page does not score penalties; read the contract.
- Revolving vs installment — Credit cards and lines of credit change every month; use the debt payoff calculator for those balances.
- APR label — Confirm whether the percent you type is the amortization rate or a fee-inclusive APR headline. See APR vs interest rate.
Frequently asked questions
Is APR the same as the interest rate I enter?
Enter the annual rate your lender quotes for amortization. Advertised APR can include fees; this tool models interest on principal only. Read APR vs interest rate before you compare two offers that quote different labels. For how each installment splits between interest and principal over the life of the loan, see loan amortization explained.
Can I model biweekly payments?
Not directly. Biweekly schedules make more payments per year; ask your lender or use a dedicated amortization schedule for that case.
Can I enter amounts in pounds?
Yes. The formula does not depend on currency. Enter £ principals and read the payment as pounds for the same loan.
A comparison you can reproduce
Enter 10,000, 5%, and 3 years: the monthly payment is 299.71 and total interest is 789.52. Change only the term to 5 years: the payment becomes 188.71 and interest becomes 1,322.74. The lower payment costs an extra 533.22 in interest over the full term, before any fees.
We calculate totals before rounding the displayed monthly payment. A lender rounding every instalment to pennies may adjust the last payment slightly. Fractional-year terms round up to a complete month; this tool supports terms up to 100 years.
Background: CFPB guide to loan amortization.
Limitations
Fees, prepayment penalties, and variable rates are not modeled. Lenders may round payments differently. Results are estimates only and are not financial advice.
Results are estimates only and are not financial advice.