Extra money can go into KiwiSaver or onto the mortgage, and each has a different kind of return: a mortgage repayment saves interest at a known rate, while KiwiSaver adds employer and government money at the default rate and then earns an uncertain market return on money that is locked in until 65. This page compares the two; the same question from the mortgage side, including investing outside KiwiSaver, is covered in pay off the mortgage or invest. Other KiwiSaver trade-off guides are on the KiwiSaver strategies hub.
The Core Trade-Off
Paying off your mortgage early gives a certain return equal to your mortgage interest rate: if your rate is 6%, each extra dollar saves 6% a year in interest, and because owner-occupiers can’t deduct mortgage interest, that saving is effectively after tax.
A KiwiSaver fund’s return is not guaranteed and varies widely from year to year; growth funds have had higher long-run returns than conservative funds, along with larger falls. How the fund types differ is in KiwiSaver fund types explained.
Employer and Government Contributions
Paying into KiwiSaver from wages triggers your employer’s contribution of at least 3.5% of gross pay, which a savings suspension generally stops as well (employer KiwiSaver contributions). Putting in $1,042.86 over a KiwiSaver year (1 July to 30 June) also earns the full $260.72 government contribution.
Those amounts come with the default rate of 3.5% (from 1 April 2026); paying in more than that brings no further employer or government money, so for the extra dollars the question is the mortgage rate against the fund’s expected return.
Mortgage Rate Against Expected Return
For money above the default rate, the comparison turns on:
- Your mortgage rate, a certain saving until the fixed term ends. Current rates are on the NZ mortgage rates page, and a refix can change the comparison.
- The fund’s expected return after fees and PIE tax, which is an assumption, not a promise, and can be negative in a given year.
- Time to retirement: the longer the horizon, the more years for a fund’s return to vary around its average.
Liquidity: Offset, Revolving Credit and Lock-In
If your mortgage is an offset or revolving credit loan, money in the account reduces interest charged daily while staying accessible.
KiwiSaver contributions, by contrast, stay put until 65 except in the cases the KiwiSaver withdrawal rules allow, a first home and financial hardship among them. Extra repayments on a fixed loan aren’t redrawable either, and fixed loans may limit how much you can repay early without a break fee, but on a floating or revolving facility they can usually be drawn back.
Worked Example
Illustration: $400,000 mortgage at 6.2% with 20 years remaining (monthly repayment about $2,912), already contributing at the default KiwiSaver rate, with $500 a month spare. The fund return is an assumption, before tax and fees.
Option A: $500 a month into KiwiSaver as voluntary contributions
- $6,000 a year for 20 years at an assumed 7% a year: about $246,000 at the end
- The return isn’t guaranteed and the money is locked in until 65
Option B: $500 a month extra on the mortgage
- Mortgage paid off in about 15 years (181 months) instead of 20
- About $83,000 less interest in total, a certain saving at 6.2%
- For the last 5 years the full repayment of about $3,412 a month is free to save or invest
The two aren’t directly comparable without assuming what happens to the freed-up repayments in Option B and what the fund returns in Option A. A lower fund return, a higher mortgage rate after a refix, or a need for the money before 65 each moves the comparison toward the mortgage; the reverse moves it toward KiwiSaver.
Frequently Asked Questions
Can I pause KiwiSaver to pay off my mortgage faster? Yes: you can apply for a savings suspension. Your employer generally stops contributing during it, and you may fall short of the $1,042.86 needed for the full government contribution, so the cost includes both, not just the contributions you redirect.
How do lump sums compare? A lump sum on the mortgage may be limited or charged a break fee on a fixed loan; a lump sum into KiwiSaver is locked in until 65. The lump sum mortgage payments guide covers the mortgage side and voluntary KiwiSaver contributions the KiwiSaver side.
What about when I refix my mortgage? A new fixed rate changes the certain saving from extra repayments, so the comparison changes at each refix. The refixing guide covers the options when a term ends.