Interest-only mortgage calculator
See your repayments during the interest-only period, how much they go up when that ends and how much extra interest you'll pay.
Fortnightly repayment, interest only
$1,199.42
| Fortnightly repayment after 3 years | $1,627.66 |
| Total interest over 30 years | $606,169 |
| Extra interest from interest-only | $26,163 |
If you paid principal and interest from the start, the fortnightly repayment would be $1,551.29 for the whole term.
Thinking about interest-only? An adviser can tell you which banks would offer it.
A licensed mortgage adviser will look at your situation and tell you which rates and loan options you might qualify for. This advice is free.
How this calculator works
An interest-only loan works in two stages. At first, you just pay the interest, so your loan balance stays the same. The calculator spreads the yearly interest rate over your repayments. When the interest-only period ends, your loan changes to a standard table loan, and you start paying off the full amount over the years left. Since you haven't paid down the loan yet and have less time to do it, your repayments are higher than if you'd paid principal and interest from the start.
The calculator starts with a $630,000 loan, which is about the national median sale price of $784,363 minus a 20% deposit, at 4.95%, the average 1-year special rate at the end of October 2026. The interest-only period is set to 3 years, the longest Westpac offers on a home you live in. You can change these numbers to match your own loan.
The calculator assumes the interest rate stays the same for the whole loan. In real life, you'll probably refix your rate during the loan, so it could change over time.