Finance & property Australia
Compound Interest Calculator Australia
Compound interest is interest earned on interest. This calculator shows what a starting balance and regular deposits grow to at a rate you choose, how much of the result is your own money and how much is interest, year by year.
Free, no signup Runs in your browser
Optional. Your marginal rate, to see the after-tax result.
Balance at the end
—Total you put in
—
Interest earned
—
Interest after tax
—
Balance after tax
—
Share that is interest
—
Balance by year
An estimate, not advice. General information and estimates only, not financial advice. Rates, fees and rules change, so check the lender's or provider's own terms and speak to a licensed adviser before you act.
How do I calculate compound interest?
Multiply the balance by one plus the periodic rate each period and add your deposits. $10,000 with $300 added each month at 5% a year for 10 years grows to $63,055, of which $46,000 is what you put in and $17,055 is interest.
Why time beats rate
Compounding multiplies a balance by the same factor every period, so the final years carry the biggest growth. Saving $300 a month for 20 years at 5% reaches about $123,000, while 10 years reaches about $46,000: doubling the time nearly triples the result.
A higher rate helps, but only by a fixed fraction each period, while extra years add whole periods.
Savings accounts and tax
Bank savings rates change often and are not guaranteed, and bonus rates may need conditions to be met. Deposits are protected by the Financial Claims Scheme, which protects up to $250,000 per account holder at each authorised deposit-taking institution. Interest is taxable income at your marginal rate, and your bank reports it to the ATO.
To test a term deposit, use the term deposit calculator.
How this is calculated
The rule, step by step, so you can check any figure by hand.
each period: balance = balance × (1 + rate ÷ periods a year) + deposit for the periodtotal put in = starting amount + deposits × monthsinterest earned = final balance − total put inafter tax: interest × (1 − your tax rate)
The power of compounding is time. At 5%, a lump sum doubles in about 14 years, and the last years of a long saving period add far more than the first. That is why starting early and leaving money untouched matter more than the exact rate.
The rate is an assumption, and savings rates move with the market. Interest is taxable income at your marginal rate, and your bank reports it to the ATO. Enter your own tax rate to see what you keep.
A worked example
$10,000 to start, $300 a month, 5% a year compounded monthly for 10 years.
- Total put in$46,000
- Balance after 10 years$63,055
- Interest earned$17,055
- Interest as a share of the balance27%
$63,055 at the end.
Compounding more often adds a little; the rate and years matter most.
Inflation
A balance in future dollars buys less than the same number today. Subtract expected inflation from your rate to see the real growth. At 5% interest and 2.5% inflation, the real rate is about 2.4%.
What it leaves out
Fees, changing rates, tax on growth other than interest and withdrawals are not modelled. Investment returns are not constant and can fall, unlike a fixed rate.
What this calculator does not do
- Constant rate and deposits
- Interest tax uses one rate
- No inflation adjustment
- Not investment advice
Common questions
What is compound interest?
Interest calculated on both the original amount and the interest already added.
How often is interest compounded?
Savings accounts usually add it monthly; term deposits may add it at the end or each month.
What is the rule of 72?
Divide 72 by the rate to estimate the years to double: at 6%, about 12 years.
Does the tool include tax?
Optionally. Enter your tax rate to see the after-tax figure.
Are my savings protected?
Deposits are covered by the Financial Claims Scheme, which protects up to $250,000 per account holder at each authorised deposit-taking institution.
Where these numbers come from
- MoneySmart — ASIC's money guidance Independent guidance and calculators on saving, borrowing and investing
Method last reviewed 2026-10-28 This calculator uses fixed rules rather than rates that change, and its method is re-checked against the sources above at least once a year. Out of date? Tell us and we will fix it.
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