What your result means
The comparison shows the modelled payoff time and interest with and without the extra amount. Paying principal earlier leaves a smaller balance for later interest calculations.
Mortgage tools · New Zealand
Mortgage extra repayment calculator NZ
Compare a standard repayment with a regular extra amount. Check your loan terms for repayment limits, fees or break costs before changing payments.
Last reviewed 19 August 2026 · Replace every default with a realistic scenario.
Your estimate
Estimated monthly repayment
$3,888
Based on a $600,000 loan
Total interest
$696,867
Paid off in
27.8 years
Total repaid
$1,296,867
Interest saved
$66,980
An unchanged-rate scenario suggests about 26 months and $66,980 in interest saved.
Estimate only: Mortgage results are planning estimates, not lender quotes, approval decisions or personalised financial advice. Actual repayments can differ because of lender methods, fees, rate changes and loan terms.
How the calculation works
For each payment period, the calculator applies interest to the remaining balance and then subtracts the scheduled payment plus the entered extra amount. It repeats this process until the balance reaches zero.
Example calculation
If the scheduled payment is supplemented by $100 every payment period, that $100 is modelled as an immediate reduction in principal. The displayed saving compares that schedule with the same loan without the extra amount.
What affects the result?
- The extra amount and how often it is paid affect the payoff time.
- A higher balance or interest rate can change the potential interest saving.
- The estimate assumes the entered rate and extra payment remain unchanged.
- Fixed-loan limits, fees or break costs can reduce the practical benefit.
New Zealand context and sources
New Zealand fixed-rate mortgage terms may limit additional repayments or impose break costs when agreed payments change. Floating loans can be more flexible but use a variable rate. Check the specific loan agreement and ask the lender how an extra payment will be applied before changing it.
Frequently asked questions
Can every fixed mortgage accept unlimited extra payments?
Not necessarily. Fixed-loan terms can limit extra repayments or include charges, so check with your lender first.
Why is the saving only an estimate?
Rates, payment timing, fees and future changes affect the actual interest and payoff date.
Does the calculator model a one-off lump sum?
No. The extra amount is treated as a regular addition to every selected payment period. A one-off repayment needs a different calculation.
Is paying extra always the best option?
Not necessarily. Cash reserves, other debts, loan terms and personal priorities matter. The calculator compares loan scenarios and does not provide personalised financial advice.
New Zealand mortgage guides
Review the calculation assumptions and current New Zealand lending context before comparing scenarios.