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Compound Interest Calculator

See how your savings grow over time with a starting deposit, regular monthly contributions and compound interest.

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More options· Compounded monthly

In 20 years you'll have

$300,851

Before fees and taxes

You put in
$130,000
Interest earned
$170,851
Your balance: contributions vs. interest
  • Your contributions43%
  • Interest57%

What this means

$170,851 of it is growth: interest earned on your interest as well as on what you put in. It speeds up over time, so the last years add the most.

Prices rise too. At 2.5% inflation a year, $300,851 in 20 years buys about what $183,600 buys today.

Next step

Balance by year, split into contributions and interest
$300,851$150,425$0
12468101214161820
ContributionsInterest
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How compound growth works

Each month, interest is added to your balance and your contribution is deposited. The next month, interest is earned on that larger balance. The chart shows how, over time, interest makes up a growing share of the total.

Getting the most from compounding

  • Start early: time is the biggest driver of growth.
  • Contribute regularly: small monthly amounts add up, and each one starts compounding right away.
  • Check your RWT rate: if your bank uses a higher rate than your income needs, you lose more of each interest payment to tax than you should.

Last updated

Frequently asked questions

What is compound interest?

Compound interest is interest earned on both your original money and the interest it has already earned. Over long periods it makes savings grow much faster than simple interest.

Is interest on savings taxed in New Zealand?

Yes. Your bank deducts resident withholding tax (RWT) from interest at a rate based on your income, so the amount you receive is after tax. This calculator shows growth before any tax.

What is the rule of 72?

Divide 72 by your annual interest rate to estimate how many years it takes for money to double. At 6%, money doubles in about 12 years.