See how savings grow when interest earns interest, year by year.
Updated October 2026Built and checked by MaverickHow it's calculatedReport an error
Final balance
$367,912
Total contributions
$130,000
Your money in
Compound interest
$237,912
What growth added
Years to double
8.5y
Rule of 72
The curve steepens over time: that's compounding doing its work.
Early on it's all your money. Later, the interest does the heavy lifting.
How each of the three drivers contributed to the final number.
The same contributions at different returns: a small gap in the rate compounds into a large gap in the balance.
Time does more of the work than the rate or how much you add.
Compound interest is interest earned on interest you've already earned. In the first few years it barely shows; after 20 or 30 it's doing most of the work. Put in what you have, what you'll add and a rate, and this shows the growth year by year, whether the money sits in a savings account, ETFs or shares.
As of 7 November 2026, the highest savings rate is 5.75%, from Defence Bank Limited's iSaver, while the typical best across 73 institutions is 4.85%. The highest 12-month term deposit rate is 5.75%, from Suncorp Bank's Term Deposit, while the typical best across 65 institutions is 5.30%. Prices rose 4.3% in the year to September 2026, so savings earning less than that lose ground to inflation, before tax.
Emma invests $500 a month from 25 to 65 at 7% a year, compounding yearly.
Emma puts in $240,000 and the balance grows to about $1.2 million - about $958,000 of it earnings, four times what she contributed. Starting 10 years later, at 35, the same plan reaches about $567,000.
James invests $50,000 and adds $200 a month for 15 years at 8%, compounding monthly.
The $50,000 grows to about $165,300 on its own and the contributions to about $69,200, for a total of about $234,600 from $86,000 put in.