Loan Calculator — Monthly Payment & Amortisation Schedule
Work out your repayment, total interest and a full payment-by-payment schedule.
🔒 Runs in your browser — files never uploaded ⚡ No signup 💯 Free
Principal — Interest —
| # | Payment | Principal | Interest | Balance |
|---|
Enter the amount, rate and term to see your repayment, how much interest you will pay in total, and a complete amortisation schedule you can download as a spreadsheet.
Works for personal loans, car finance, student loans and mortgages, with monthly, fortnightly, weekly or quarterly repayments.
How to use Loan Calculator
- Enter the loan amount you are borrowing.
- Enter the annual interest rate. Use the nominal rate the lender quotes, not the APR, unless the APR is the only figure you have.
- Set the term and frequency.
- Open the amortisation schedule to see how each payment splits between principal and interest.
How the payment is calculated
We use the standard annuity formula, the same one lenders use:
Payment = Principal × r ÷ (1 − (1 + r)^−n)
where r is the interest rate per period and n the total number of payments. The schedule is then built payment by payment, so rounding accumulates exactly as it does on a real loan ledger and the final instalment absorbs any residual pennies.
Why early payments are almost all interest
Interest each period is charged on the balance still outstanding. At the start that balance is nearly the whole loan, so most of your payment goes to interest and only a sliver reduces the principal. As the balance falls the split reverses. On a 25-year mortgage, roughly the first seven years go mostly to interest — which is why overpaying early has a disproportionate effect.
Paying fortnightly instead of monthly
Switching to fortnightly payments of half the monthly amount means 26 half-payments a year — the equivalent of 13 monthly payments rather than 12. That single extra payment a year can cut several years off a long loan. Change the frequency above to compare.
What this does not include
Arrangement fees, insurance, property taxes and early-repayment charges are excluded. For a mortgage, your real monthly outgoing will be higher than the figure here.
Frequently asked questions
Is this the same formula my bank uses?
Yes — the standard annuity formula. Small differences in the final total can arise from how a lender rounds each instalment and whether they charge interest daily or per period.
Why is so much of my early payment interest?
Interest is charged on the outstanding balance, which is nearly the whole loan at the start. As the balance falls the split shifts toward principal. This is also why overpaying early saves disproportionately more.
Does this include fees, insurance or taxes?
No. It calculates principal and interest only. Arrangement fees, mortgage insurance and property taxes are extra, so your real monthly outgoing will be higher.
Should I enter the interest rate or the APR?
Use the nominal interest rate the lender quotes. APR bundles fees into a single figure for comparison purposes and will slightly overstate the payment if entered here.