Methodology & sources
How this calculator works
Calculation method
The starting balance grows as start × (1 + r/m)^(m × years), where r is the nominal annual rate and m is the compounding frequency (daily 365, monthly 12, quarterly 4, half-yearly 2 or annually 1). Each regular contribution earns the effective rate for its own period, (1 + r/m)^(m/p) − 1, where p is the contribution frequency (weekly 52, fortnightly 26, monthly 12, quarterly 4 or annually 1), and contributions are summed as an annuity at that rate.
End-of-period timing adds each contribution at the end of its period. Start-of-period timing adds it at the beginning, so every contribution earns one extra period of growth. Only whole contribution periods within the horizon receive a contribution; with fractional years, any trailing partial period simply compounds. Interest earned is the balance minus the starting balance and contributions. When an inflation rate above zero is entered, the balance is also divided by (1 + inflation)^years to show it in today’s dollars. The year-by-year table uses the same formula, so its final row matches the projected balance.
Worked example
At the default $10,000 starting balance, $250 monthly contribution at the end of each month, 6% annual rate compounded monthly and a 10-year horizon, the projected balance is $59,163.80. Of that amount, $40,000 is contributed and $19,163.80 is interest earned. Contributing at the start of each month instead gives $59,368.65.
With the same figures, annual compounding gives $58,526.84, quarterly $59,043.94 and daily $59,222.45. A $115 fortnightly contribution gives $59,082.14 from $39,900 contributed. At 2.5% inflation, the default $59,163.80 is about $46,218.67 in today’s dollars. Real returns can vary.
Assumptions and limitations
- The entered annual rate is a nominal rate compounded at the selected frequency and stays constant.
- Contributions are made every period at the selected frequency and timing; a trailing partial period receives no contribution.
- No withdrawals, additional one-off deposits or missed contributions occur.
- Fees and tax are excluded; inflation only affects the optional today’s-dollars figure.
- The calculation does not account for the risk, liquidity or suitability of any investment.
- Editable interest rates, returns, growth rates and fees are scenario assumptions, not live market quotations. Use your current lender or provider figures; the RBA cash rate is not a retail loan rate.
Official sources
Methodology documented: 21 September 2026. The methodology documentation date records when this explanation was prepared. It is not a financial-rules verification date. Check the linked official sources for current rules before relying on a tax, duty, grant or product-related estimate.