Loan Calculator

Features

• Monthly, fortnightly or weekly payment schedules
• Full amortization table summarised by year
• Extra-payment modelling with interest saved
• Total repaid and total interest breakdown
• Exports the schedule as CSV

How to use it

1. Enter the loan amount, rate and term.
2. Add an extra payment amount to see its effect.
3. Read the payment and total interest above.
4. Download the schedule if you need it in a spreadsheet.

How amortization actually works

An amortizing loan uses a fixed payment split between interest and principal, but the split shifts over time. Interest is charged on the outstanding balance, so early payments are mostly interest and barely dent the principal. On a 25-year mortgage at 5.5%, roughly 70% of the first payment is interest; by the final year that has fallen below 5%. This is why a loan's balance drops slowly at first and then accelerates.

It is also why extra payments are disproportionately effective early on. Any additional amount goes entirely to principal, which removes all the future interest that balance would have generated. Paying an extra 10% each month on a typical 25-year mortgage often cuts four to five years off the term and saves a substantial multiple of what you actually paid in.

Two caveats on the numbers here. This calculates a straightforward amortizing loan and does not include property taxes, insurance, arrangement fees or mortgage insurance, all of which can add materially to what you actually pay each month. And it assumes a fixed rate for the whole term, a variable or tracker rate will diverge from these figures as soon as the rate moves.