Compound Interest Calculator
See how a starting balance and regular monthly contributions grow over time. Adjust the rate and the timeline to see the magic of compounding for yourself.
Long-run ASX 200 has averaged ~7-10% p.a. before inflation. 7% is a common conservative estimate.
Final balance · 30y
$691k
Total contributed
$180k
Interest earned
$501k
Balance growth over time
Started 5 years earlier? You'd have $1.02M instead.
That's an extra $324k from compounding alone — same monthly contribution, same rate, just more time. This is why time in the market beats timing the market.
Want to see this against your whole financial picture — super, tax, expenses, retirement?
Try the full planDisclaimer: This calculator provides estimates for general information purposes only. Results may not be 100% accurate and should not be relied upon for financial decisions. Tax rules, rates, and thresholds change — always verify with the ATO, official government sources, or a qualified financial adviser, tax professional, or accountant. This is not financial advice.
What is compound interest?
Compound interest is the interest you earn on your interest. Each period, the return is calculated on the new, higher balance — including everything the account has previously earned. Over long horizons this snowballs, and the interest you earn eventually dwarfs the money you originally put in.
This calculator assumes monthly compounding with regular monthly contributions, which is how most Australian savings accounts, ETFs, and super balances are typically modelled.
Why starting early matters
The same monthly contribution started 5 or 10 years earlier can be worth dramatically more by retirement, because the early dollars have many more years to compound. The “Started 5 years earlier?” callout above shows exactly how much extra balance you would have on the same inputs — typically tens of thousands more for a few hundred dollars a month.
What rate of return should I use?
For long-run Australian equities, a common assumption is 7% per year before inflation. Broad-market ETFs like VAS, A200 and STW have historically averaged 7-10% including dividends and capital growth, but actual returns vary year to year and past performance is no guarantee of future results.
For high-interest savings accounts, the rate is usually closer to the cash rate plus a margin (around 4-5% in 2025). For mortgage offset accounts, treat the offset as an effective return equal to your home loan rate.
What this calculator does not include
This is a simple compound-interest illustration. It does not account for:
- Tax on dividends, interest, or capital gains
- Inflation eroding the purchasing power of the final balance
- Variable returns and sequence-of-returns risk (real markets aren't a smooth line)
- Fees, brokerage, or platform costs
- Australian super contribution caps and the 15% contributions tax
For a model that includes all of the above against your full financial picture, try the JettWorth play mode — no sign-up required.
Important: this is not financial advice
JettWorth is an insights platform, not a licensed financial adviser. Numbers shown here are projections based on the assumptions you enter and standard mathematical formulas. Real investments fluctuate, fees apply, and tax matters. Always consult a qualified financial adviser, accountant, or tax professional before acting on what you see here.