How much can I save by paying extra off my mortgage each month?

The savings depend on your loan balance, interest rate, remaining term, and extra payment amount. As a general guide, on a $500,000 mortgage at 6.5% over 25 years, paying an extra $200 per month saves approximately $75,000 in interest and cuts around 3 years off the loan. The earlier in the loan term you start making extra payments, the greater the savings, because interest is front-loaded in a standard principal-and-interest mortgage.

Does making extra payments reduce my required monthly repayment?

No. Extra payments reduce the loan principal faster, which shortens the time it takes to pay off the loan and reduces the total interest charged. Your required minimum repayment stays the same unless you formally restructure the loan. The extra payments simply mean you reach a zero balance sooner. Some lenders allow you to redraw extra payments later if you need the funds, so check whether your mortgage has a redraw or offset facility.

Can I make lump sum extra payments on a fixed-rate mortgage in NZ?

Most New Zealand banks allow lump sum extra repayments on fixed-rate mortgages up to a certain annual cap without break fees, commonly 5% to 20% of the outstanding balance per year depending on the lender and mortgage product. Payments above that threshold during a fixed-rate period may incur a break fee. On floating rate mortgages, extra payments can typically be made at any time without penalty. Always check your loan agreement or ask your bank before making large lump sum payments.

Mortgage with Extra Payments Calculator

See how much interest you save and how many years you cut off your mortgage by making extra repayments. Enter your loan details and an extra monthly or lump sum payment to compare your two scenarios side by side.

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Updated June 2026 Standard principal-and-interest amortisation formula. Applicable to all NZ home loans.

1. Your Mortgage

Loan balance (remaining principal)

Annual interest rate % p.a.

Remaining loan term

Repayment frequency

2. Extra Payments

Extra amount per repayment (on top of minimum)

One-off lump sum (optional) paid today

When does extra payment start?

Your Savings Summary

Standard Repayment

Per repayment (minimum)

Time Saved

Loan paid off sooner

Interest Saved
-
Total interest reduction

New Payoff Date

vs original: -

Without Extra Payments

Loan balance-

Interest rate-

Loan term-

Minimum repayment-

Total repayments-

Total interest paid-

With Extra Payments

Extra per repayment-

Lump sum paid today-

New total repayment-

New loan term-

Total repayments (new)-

Total interest paid-

Savings at Different Extra Payment Amounts

Extra per repayment	New term	Years saved	Interest saved	Total interest paid

Summary: Enter your loan details above.

How Extra Mortgage Payments Work

A standard principal-and-interest mortgage has a fixed repayment calculated so that, at the agreed interest rate, the loan balance reaches zero at the end of the term. Early in the loan, most of each repayment covers interest; only a small portion reduces the principal. Over time, as the principal falls, less interest accrues each period and more of the fixed repayment goes toward principal.

When you pay more than the minimum, the extra amount is applied directly to the principal. A smaller principal means less interest charges in every subsequent period. This compounds across the life of the loan: each extra dollar paid today saves more than one dollar in future interest. The result is a shorter loan and a lower total cost.

The Maths Behind the Calculator

The standard minimum repayment is calculated using the annuity formula:

Variable	Description
P	Loan principal (balance)
r	Periodic interest rate (annual rate divided by number of periods per year)
n	Total number of repayment periods (years x periods per year)
M	Minimum repayment = P x r x (1+r)^n / ((1+r)^n - 1)

When extra payments are added, the calculator runs a period-by-period amortisation: starting from the current balance, it applies interest for each period, subtracts the total payment (minimum plus extra), and records the remaining balance. Any lump sum is applied to the balance in the first period. The loop ends when the balance reaches zero, giving the actual new payoff date.

Worked Example

Using the default inputs: $500,000 loan, 6.5% interest rate, 25-year term, $200 extra per month.

Monthly rate: 6.5 / 12 / 100 = 0.54167%
Minimum monthly repayment: approximately $3,377
Total interest without extra payments: approximately $513,000
With $200 extra per month: the loan is paid off in roughly 21 years and 11 months, saving approximately $75,000 in interest and just over 3 years

The earlier you start making extra payments, the greater the saving. Starting extra payments 2 years into a loan saves noticeably less than starting immediately, because the principal is higher in the early years and interest compounds faster.

Tips for Making Extra Payments in New Zealand

Check your break fee rules: on a fixed-rate mortgage, most NZ banks allow up to 5% to 20% of the outstanding balance in lump sum payments per year without a break fee. Check your loan agreement.
Use a revolving credit or offset account: if your lender offers one, parking extra savings there can reduce your interest daily without locking the money away.
Increase your direct debit: the simplest way to make extra repayments is to round up your regular payment and instruct your bank to pay the higher amount each period.
Pay fortnightly instead of monthly: switching from monthly to fortnightly repayments effectively makes one extra monthly payment per year, which can cut several years off a standard 25 or 30 year mortgage.
Apply windfalls: tax refunds, bonuses, or inheritances applied as lump sums have an outsized impact on long mortgages because they reduce the principal the interest compounds on.

Related Calculators

Mortgage Calculators: full hub for all NZ home loan tools.
Mortgage Extra Repayment Calculator: focused extra repayment analysis.
Mortgage Repayment Calculator: standard monthly repayment and total interest.
Mortgage Amortisation Schedule: full period-by-period breakdown of principal and interest.
Mortgage Lump Sum Impact Calculator: effect of a single lump sum payment.

Method: Standard principal-and-interest amortisation using the annuity formula M = P x r(1+r)^n / ((1+r)^n - 1). Extra payments are applied period by period as a reduction to the outstanding principal. Lump sum is applied at the start of the first period before interest accrues. All figures in New Zealand dollars. This calculator is for indicative purposes only. Consult your lender or a registered financial adviser before making changes to your mortgage structure.