Short answer: compounding is earning returns on your past returns as well as on the money you put in. In KiwiSaver it is the main reason small, consistent contributions made early tend to matter more than larger ones made late.
Key points: time is the ingredient you cannot buy back, so the years your money stays invested do most of the work. Fees compound too, in the wrong direction, which is why a small ongoing difference in cost or return can change the end result substantially.
Worth checking: KiwiSaver returns are not a fixed interest rate - your balance can fall as well as rise, so the smooth curve in any example is illustrative rather than a forecast. Model your own numbers with Sorted's savings calculator.
Compound interest is when you earn returns not just on your original money, but on the returns that money has already earned. Over time this creates a snowball effect - your savings grow faster and faster because you're earning on a bigger and bigger amount.
A simple example
Say you make a one-off investment of $1,000 earning 10% a year.
| Year | You earn | Total |
|---|---|---|
| Year 1 | $100 | $1,100 |
| Year 2 | 10% of $1,100 | $1,210 |
| Year 3 | 10% of $1,210 | $1,331 |
Each year the dollar amount you earn gets bigger, even though the rate never changes. Keep that going and after 40 years your $1,000 becomes about $45,259 - without you adding another cent. (This is an illustration at a constant 10% - real KiwiSaver returns vary year to year - but the compounding principle is exactly the same.)
Einstein reputedly called compound interest the eighth wonder of the world: those who understand it, earn it; those who don't, pay it.
Why this matters for your KiwiSaver
KiwiSaver is a long-term investment, which puts compounding firmly on your side - the earlier you start contributing and the better your returns, the more powerfully it works. Three practical consequences:
Time beats timing. Money invested in your twenties has decades more compounding runway than money invested in your forties. This is why starting early - even starting your kids early - matters so much.
Small return differences become huge. A fund earning even 1% more per year, compounded over 30-plus years, can mean tens of thousands of dollars of difference. That's why your fund type matters more than most people realise.
Contributions early in life punch above their weight. Every dollar in early gets the longest ride. Want to see your own numbers? Run your projection in the KiwiSaver calculator.
If the barrier is finding spare money to contribute in the first place, small and automatic beats large and occasional. One approach some Kiwis use is rounding up spare change into KiwiSaver, which is compounding applied to amounts you would not otherwise notice.
Frequently asked questions
Does KiwiSaver actually pay "interest"?
Not in the bank-account sense - your KiwiSaver is invested in funds that earn returns from shares, bonds and other assets. But those returns compound in exactly the same way: gains are reinvested and generate their own gains over time.
How do I make compounding work harder for me?
Start early, contribute consistently, make sure you're in a fund type matched to your timeframe, and check your provider's long-term net returns (after fees). A free advice session can cover all four in half an hour.
Sources and further reading
Primary New Zealand sources for the points above. Rules change, so check the current position before acting:
- Sorted KiwiSaver savings calculator - independent projections using your own figures.
- Inland Revenue - how KiwiSaver works - how contributions and returns build your balance.
- Inland Revenue - government contribution - the annual top-up that compounds alongside your own money.
- Sorted - which KiwiSaver fund suits you - how fund choice affects long-term growth.
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