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Interactive calculator

Compound interest calculator.

Growth on your growth. Choose your own rate, add regular contributions, and see exactly how much of the final number compounding does for you.

Your numbers

Everything updates as you type. Nothing is stored or sent anywhere.

% p.a.

We don't suggest a rate – returns aren't guaranteed. Enter your own assumption (after fees/tax if you want a net picture).

$
$
years
Compounding frequency

After 25 years you'd have

–

Type a growth rate on the left to see your total.

Contributions vs growth

Contributions Growth

How this compound interest calculator works

The calculator simulates your balance day by day. At your chosen compounding frequency it applies your growth rate; at your chosen contribution frequency it adds your contribution. The chart then splits the result into two layers: the money you put in, and the growth that compounding added on top. Because you set the growth rate yourself, the result is your scenario – not a prediction, and not a promise.

Why compounding matters so much for KiwiSaver

KiwiSaver is compounding's natural habitat: decades of time, regular contributions from every pay, and returns reinvested automatically. Two things fall straight out of the maths. First, time is the heavyweight – money contributed in your twenties can out-grow much larger amounts contributed in your fifties. Second, small regular amounts beat occasional big ones, because every contribution starts compounding from the day it lands. If the growth slice of your chart surprises you, that's the lesson working.

The honest fine print

Real investment returns arrive unevenly – good years, flat years and negative years – rather than in a smooth line, and this calculator compounds a single steady rate. It ignores tax, fees and inflation unless you build them into the rate you enter. It's a general information tool for understanding how compounding behaves, not financial advice and not a projection of any fund.

The bigger picture

Compounding works best on a plan that's protected

Decades of compounding only happen if the contributions keep flowing. We advise on your KiwiSaver, and our sister company Insurance People – an Authorised Body under the same FMA licence – advises on the cover that keeps illness, injury or the unexpected from cutting the compounding short. One family of advisers, so the two sides actually talk to each other.

Compound interest questions, answered

What is compound interest?
Compound interest is growth on your growth. Your money earns a return, that return is added to your balance, and the next return is calculated on the new, bigger balance. Over short periods the effect is small; over decades it snowballs, which is why the later years of a long-term investment usually add far more dollars than the early years.
What growth rate should I type in?
That's your call, and it's the honest answer: we deliberately don't suggest a rate, because no rate is guaranteed and past returns are not a reliable guide to future returns. Different fund types have historically produced very different long-term returns. If you'd like help choosing a realistic assumption for your situation, talk to a financial adviser – that's what we do all day.
Does this calculator include tax, fees or inflation?
No – it compounds exactly the rate you enter. If you want an after-fees, after-tax picture, enter a rate with fees and tax already taken off. If you want the result in today's buying power, enter a rate with inflation taken off as well (a 'real' return). The result can only ever be as realistic as the rate you choose.
How often does KiwiSaver actually compound?
KiwiSaver funds are unit-priced: the fund's value is recalculated (typically every business day) and your returns are effectively rolled into your balance continuously, rather than being credited monthly like a bank account. That behaviour is closest to the daily compounding option, which is why it's this calculator's default.
Why does contributing regularly make such a difference?
Every contribution starts its own compounding clock. Money added early has decades to grow, and even modest regular amounts build a surprisingly large 'growth' slice over time. The chart on this page splits your final balance into what you put in versus what growth added, so you can see exactly how much of the total the compounding did.
Can I share my result?
Yes – the share button creates a short link that reopens this calculator with your exact numbers pre-filled. Nothing is stored about you: the link only contains the inputs you see on screen.
Is this financial advice?
No. This is a general information tool using assumptions you choose. It doesn't consider your personal situation and it never recommends a fund or provider. For personalised KiwiSaver advice, book a chat with one of our advisers.
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