High Interest Savings & Compound Interest Calculator
See how your savings could grow as you add money and earn interest. Allow for bonus rates, tax and rising prices.
How this tool works
Reviewed 6 September 2026. Standard Australian ADI monthly compound interest conventions and ATO marginal income tax rules.
Calculation outline
- Uses one twelfth of the annual rate on the opening monthly balance, then adds contributions at month end. This approximates bank daily-balance calculations.
- Switches from the introductory rate to the ongoing rate when the introductory period ends.
- Models Australian tax by reducing credited interest by personal marginal tax brackets (including 2% Medicare levy).
- Adjusts the future balance for inflation to show its value in today’s dollars.
Worked example
Example: $10,000 initially plus $500 at the end of each month produces $40,000 of deposits over five years. Interest is added separately using the entered rates; the selected flat tax rate reduces each month’s interest.
Limits
- Assumes constant interest rates throughout the projection period; Australian bank rates move in response to RBA cash rate decisions.
- Assumes no withdrawals or penalty fee events that void bonus interest criteria.
Sources
- ASIC Moneysmart compound interest calculator
- ATO individual income tax rates
- Reserve Bank of Australia inflation target
This tool provides general information and illustrative estimates only. It does not consider your objectives, financial situation or needs and is not personal financial, tax or legal advice.