How Extra Mortgage Repayments Save You Money
Every dollar you overpay — also called an extra repayment — goes directly to reducing your loan principal. Because your lender calculates interest on your outstanding balance, a lower principal means less interest charged the very next month — and the month after, and the month after that. This compounding effect is why extra repayments made early in a loan save far more than the same amount made later.
On a typical home loan, the difference between paying the minimum and overpaying a modest amount can be hundreds of thousands of dollars in total interest over the life of the loan — and years off your mortgage term.
How Much Can You Save? Real Numbers
The table below shows the estimated interest saved and time cut from a $600,000 loan at 6.00% over 30 years for different extra monthly repayment amounts. These are indicative figures — use the calculator above to model your exact loan.
| Extra per month | Interest saved | Years saved |
|---|---|---|
| $100 | ~$58,000 | ~2 years |
| $200 | ~$107,000 | ~4 years |
| $500 | ~$213,000 | ~8 years |
| $1,000 | ~$321,000 | ~12 years |
Figures are estimates only. Actual savings depend on your loan balance, rate, remaining term, and when extra repayments begin.
When to Start Making Extra Repayments
The single biggest factor determining how much you save is when you start. In the early years of a 30-year mortgage, the majority of every minimum repayment is interest — your principal barely moves. Extra repayments at this stage eliminate years of compounding interest charges before they accrue.
Starting extra repayments in year one versus year ten on the same loan can mean the difference of tens of thousands of dollars in savings, even if the monthly extra amount is identical. If you can only afford a small amount extra, starting early still beats waiting until you can afford more.
Lump Sum Repayments: Tax Refunds, Bonuses & Windfalls
A one-off lump sum payment — a tax refund, work bonus, or inheritance — can have an outsized impact when applied directly to your mortgage. Because it immediately reduces your principal, it lowers the base on which all future interest is calculated. A $15,000 lump sum paid in year five of a $600,000 loan at 6% saves roughly $40,000–$50,000 in interest over the remaining term.
Use the Ad-Hoc Extra Repayments section in the calculator above to model a specific lump sum on any future date and see the exact impact on your loan payoff timeline.
Extra Repayments vs an Offset Account
Both strategies reduce the interest you pay, but they work differently. Extra repayments permanently reduce your loan balance — the money is gone from the loan, though many variable loans offer a redraw facility to access it. An offset account keeps the money liquid: the balance is subtracted from your loan balance when interest is calculated, so you pay interest on a lower amount without actually reducing the loan.
For most owner-occupiers on a variable rate, the interest saving is mathematically equivalent. The choice comes down to whether you want flexibility (offset) or a forced saving discipline (extra repayments). If your loan does not include an offset account, extra repayments are the most direct way to reduce your total interest cost.
The Turning Point — When Do You Start Paying Off Your Home?
One of the most useful things this calculator shows is your turning point — the specific month when more than half of your repayment finally goes to principal rather than interest. On a 30-year loan at 6%, that crossover arrives at year 19, month 7. For nearly two decades, the majority of every repayment you make goes to your lender, not your equity.
Extra repayments move this date forward significantly. An extra $200/month brings the turning point to year 16 — three years earlier. An extra $500/month brings it to year 13, six years earlier. After the turning point, your repayments start doing progressively more work, and the final years of the loan are paid off much faster than the first. The calculator marks your turning point on the results chart so you can see exactly when it falls under your plan.
Modelling Rate Changes
Variable mortgage rates can move significantly following central bank decisions. The calculator lets you add future rate changes on specific dates — useful if your fixed rate period is ending, or if you want to stress-test your repayment plan against potential rate increases. You can add as many rate change scenarios as you like and see how each one shifts your payoff date and total interest.