Mortgage Calculator
Calculate home loan repayments — then compare renting vs buying or model side-by-side scenarios with an interactive amortisation chart.
Split the loan between 2 or more people. Each person's share of repayments, interest and equity is calculated based on their nominated percentage. Percentages must total 100%.
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Compare the wealth outcome of buying a home vs renting and investing the difference. The model tracks mortgage repayments, interest, maintenance and capital growth against equivalent rent, investment contributions and compound returns.
Override the base calculator costs & fees for this comparison. Leave blank to inherit the base values.
Net wealth over time
Year-by-year comparison
Add alternative mortgages to compare side by side. Leave a field blank to inherit the base values — only change what you want to test.
Balance remaining
Scenario summary
How mortgage repayments are calculated
The standard mortgage repayment formula for a principal‑and‑interest loan is:
M = P × r(1+r)n / ((1+r)n − 1)
where P is the loan amount (principal), r is the periodic interest rate (annual rate ÷ number of payments per year), and n is the total number of repayments. This calculator simulates every period so it can handle interest‑only periods, extra repayments and changes in frequency exactly.
Worked example: $320,000 loan at 6.5% for 30 years
| Period | Repayment | Interest | Principal | Balance |
|---|---|---|---|---|
| Month 1 | $2,023 | $1,733 | $290 | $319,710 |
| Month 12 | $2,023 | $1,704 | $319 | $314,622 |
| Year 5 | $2,023 | $1,532 | $491 | $283,787 |
| Year 15 | $2,023 | $858 | $1,165 | $158,231 |
| Year 30 | $2,023 | $11 | $2,012 | $0 |
Over 30 years you repay about $728,280 — $320,000 principal plus $408,280 in interest. Adding just $150/month extra cuts the term by ~5 years and saves ~$100,000 in interest.
Key factors that affect your mortgage
- Deposit size. A 20% deposit avoids PMI/LMI and reduces the principal — less interest over the life of the loan.
- Interest rate. Even 0.5% difference compounds into tens of thousands over 30 years.
- Loan term. Shorter terms mean higher repayments but dramatically less total interest.
- Extra repayments. Small regular extras compound into huge savings — use the comparison tool to see the impact.
- Repayment frequency. Fortnightly or weekly repayments slightly reduce total interest because principal reduces sooner.
Frequently asked questions
How is a mortgage repayment calculated?
Using the formula M = P × r(1+r)n / ((1+r)n − 1) for P&I loans. This calculator simulates every period to handle interest‑only periods and extra repayments exactly.
What is PMI/LMI?
Private Mortgage Insurance (PMI) — or Lenders Mortgage Insurance (LMI) in some countries — is required when your deposit is below 20%. It protects the lender, not you. Enable it in Advanced options.
Is it better to rent or buy?
It depends on property appreciation, investment returns, and how long you stay. The Rent vs Buy comparison models both paths so you can compare net wealth at every year.
How do extra repayments save money?
Extra repayments reduce your principal faster, which means less interest accrues each period. Even small additional payments can shave years off your loan and save thousands in interest.
What is an amortisation schedule?
A table showing each payment broken into interest and principal portions. Early payments are mostly interest; over time the principal share grows as the balance reduces.
What is stamp duty / transfer tax?
A government tax on property purchases. The name and rate vary by country — stamp duty (UK, Australia), transfer tax (US), registration duty (India). Add it in Advanced options.