How the mortgage calculator works
Enter your loan amount, the annual interest rate, and the loan term in years, then press Calculate. You'll see your estimated monthly repayment, the total you'll repay over the life of the loan, and the total interest. You can open the amortisation schedule to see how each repayment is split between principal and interest over time.
The offset account calculator
After you calculate your loan, try the built-in offset account calculator. An offset account is a savings or transaction account linked to your home loan: its balance is subtracted from your loan balance before interest is charged, so you pay interest on less. For example, with a $500,000 loan and $30,000 sitting in your offset, you're only charged interest on $470,000.
The calculator shows both ways people use an offset: keeping your repayment the same so you pay the loan off years earlier and save interest, or keeping the term the same so your required monthly repayment drops. Most people choose the first — they simply leave their savings in the offset and let the loan finish early.
What affects your repayment
- Loan amount — a larger loan means higher repayments and more total interest.
- Interest rate — even a small rate change has a big effect over 25–30 years.
- Loan term — a longer term lowers the monthly repayment but increases total interest.
- Offset balance — the more you keep in your offset, the less interest you're charged.
Assumptions & What's Not Included
To keep results clear and fast, this calculator makes some simplifying assumptions. Knowing them helps you read the numbers correctly:
- Principal & interest only — the repayment covers loan principal and interest. It does not include property taxes/council rates, home & contents insurance, lenders mortgage insurance (LMI), establishment or ongoing account fees, or any escrow/property-cost bundling.
- Fixed rate for the full term — the interest rate you enter is assumed constant for the entire loan. Real variable rates change over time, which will alter your repayments and total interest.
- Monthly compounding & monthly repayments — interest is calculated monthly and one repayment is made per month. Choosing weekly or fortnightly repayments in real life would slightly reduce total interest.
- Payment timing — each repayment is treated as occurring at the end of the month, after that month's interest has accrued.
- No lump sums or offset unless entered — extra repayments aren't modelled here (see the offset feature for that). Redraw, repayment holidays, and rate buffers aren't included.
These figures are estimates for general guidance only, not a loan quote or financial advice. Always confirm exact repayments, rates, and fees with your lender.
Worked example
Say you borrow $500,000 over 30 years at a 6% annual interest rate, with no offset account.
| Loan amount | $500,000 |
| Interest rate | 6% p.a. |
| Term | 30 years |
| Monthly repayment | $2,998 |
| Total interest | $579,190 |
| Total repaid | $1,079,190 |
What it tells you: You’d pay about $2,998 a month, and over the full 30 years the interest alone (~$579,000) exceeds the amount borrowed. It’s why even a small rate change, or extra repayments, makes a big difference to the total.
Frequently Asked Questions
How does an offset account save me money?
An offset account is linked to your home loan and its balance is subtracted from your loan balance before interest is calculated. So if you owe $500,000 and have $30,000 in your offset, you are only charged interest on $470,000. Keeping money in your offset reduces the interest you pay and can shorten your loan term.
How is my monthly mortgage repayment calculated?
It uses the standard amortising loan formula based on your loan amount, annual interest rate, and term. Each repayment covers the interest accrued that month plus a portion of the principal, with the split shifting toward principal over time.
Does this calculator include fees or insurance?
No. It estimates the principal-and-interest repayment only. Real mortgages may include establishment fees, lenders mortgage insurance, ongoing fees, and property costs such as rates and insurance, which this tool does not factor in.
Is this calculator private? Do you store my data?
Yes, it is completely private. Every calculation runs locally in your browser, so the figures you enter are never sent to a server, never stored, and never shared. There are no accounts and no sign-up.
More Free Calculators