Time and interest saved with extra repayments.
Interest saved
—
Time saved
—
New payoff time
—
Your breakdown
Updates live as you type| Standard | Plus $300/mth |
|---|
Why a few hundred dollars a month moves the needle
A New Zealand mortgage charges interest on whatever you still owe. Every dollar of principal you knock off early is a dollar that stops accruing interest for the entire remaining life of the loan. That is the whole story behind extra repayments, and it is why the savings look almost too large to believe. The dollar you pay down in year two would otherwise have been sitting there compounding against you for another 28 years. This tool runs your loan month by month, once at the standard repayment and once with your extra on top, and reports the gap in interest and in time.
The effect is heavily front-loaded. Extra payments in the early years, when the balance is largest and almost all of your repayment is interest, do far more work than the same payments late in the term. If you are going to commit to overpaying, the sooner you start the better the return.
Adding $300 a month to a $600,000 loan
Take a $600,000 mortgage at 6.5 percent over 30 years. The scheduled repayment is $3,792 a month. Pay $4,092 instead, just $300 more, and the loan clears in 24 years and 5 months rather than the full 30. The interest you never pay comes to roughly $167,837.
Spend $300 extra for 293 months and you outlay about $87,900 more in principal sooner, yet you avoid nearly $168,000 of interest. That gap is the prize.
The fixed-rate trap to check first
Before you increase your payment, confirm your loan actually lets you. Most New Zealand banks let you overpay freely on a floating rate or a revolving credit facility. On a fixed rate the bank usually allows extra repayments up to a limit, often around 5 percent of the balance a year, and charges a break fee if you go over. Pay too much into a fixed loan and you can be hit with a cost that wipes out the saving. The clean workaround many people use is to direct the extra into an offset or revolving credit account instead, where it reduces interest without breaching the fixed-rate terms.
Expert judgement on whether to overpay at all: compare the certainty of saving at your mortgage rate against other uses of the cash. Clearing a 6.5 percent mortgage is a guaranteed, tax-free 6.5 percent return, which is hard to beat with risk-free alternatives. But if you carry higher-cost debt, a credit card or car loan, clear that first. And keep an emergency buffer, because money tipped into the mortgage is hard to get back out unless you have a redraw or revolving facility.
Is it better to make a lump sum or raise the monthly payment?
Both work, and the mechanism is identical: less principal means less interest. A lump sum early, say a bonus or inheritance, has an outsized effect because it hits when the balance is high. A higher monthly payment is the disciplined version that most people find easier to sustain. If you can do both, a lump sum now plus a modest monthly top-up is the strongest combination.
Will my repayment drop, or just the term?
By default the bank keeps your repayment the same and shortens the term, which is what this calculator models and where the big interest saving comes from. You can usually ask the bank to instead recast the loan and lower the required payment over the original term, but that throws away most of the benefit. Keep the payment up and let the term fall. The one situation where lowering the payment makes sense is genuine financial stress, where buying back some monthly breathing room is worth more than the long-run interest, but for anyone with the means to keep paying, holding the repayment steady is almost always the better call.