An investment calculator helps you estimate how much your money may grow over time, given assumptions about return rates, contribution amounts, fees, and time horizon. Understanding the calculation behind the number is as important as the result — it lets you test different scenarios and understand what drives your outcome.
The Core Formula: Lump Sum Investment
For a single lump sum invested with no additional contributions:
$$FV = PV \times (1 + r)^n$$
Where:
- $FV$ = Future Value (what you end up with)
- $PV$ = Present Value (your starting amount)
- $r$ = Annual return rate (as a decimal — 7% = 0.07)
- $n$ = Number of years
Australian example: $50,000 invested for 20 years at 7% annual return:
$$FV = $50{,}000 \times (1.07)^{20} = $50{,}000 \times 3.87 = $193{,}484$$
With Regular Contributions (Dollar-Cost Averaging)
Most Australian investors add regular contributions. The formula for future value with regular contributions:
$$FV = PV \times (1+r)^n + PMT \times \frac{(1+r)^n - 1}{r}$$
Where:
- $PMT$ = Regular payment per period (monthly contribution in annual terms: multiply monthly by 12 when $r$ is annual)
Australian example: $20,000 starting balance + $500/month ($6,000/year) for 25 years at 7%:
| Component | Calculation | Result |
|---|---|---|
| Starting balance growth | $20,000 × (1.07)^25 | $108,548 |
| Contributions growth | $6,000 × [(1.07^25 – 1) / 0.07] | $379,494 |
| Total | $488,042 |
Total contributions over 25 years: $20,000 + (25 × $6,000) = $170,000. Growth: $318,042.
Adjusting for Fees
Investment fees reduce your effective return. Replace $r$ with $(r - \text{fees})$:
| Gross return | MER | Net return | $50K over 30 years |
|---|---|---|---|
| 8.0% | 0.07% (VAS) | 7.93% | $491,000 |
| 8.0% | 0.50% | 7.50% | $435,000 |
| 8.0% | 1.00% | 7.00% | $381,000 |
| 8.0% | 1.50% | 6.50% | $332,000 |
| 8.0% | 2.00% | 6.00% | $287,000 |
A 1.5% fee difference costs ~$200,000 over 30 years on a $50,000 investment. See the Brokerage Fee Calculator for transaction cost analysis.
Adjusting for Inflation
Nominal returns include inflation — real returns strip it out. Australia’s long-run inflation has averaged around 2.5–3.0% per annum (ABS CPI data).
Real return formula: $\text{Real return} \approx \text{Nominal return} - \text{Inflation}$
If your portfolio returns 8% and inflation is 3%, your real return is approximately 5%. Modelling in real terms shows what your money buys — not just what it nominally adds up to.
Adjusting for Tax (Outside Super)
Investment returns outside super are subject to tax. Key Australian considerations:
Capital gains: 50% CGT discount for assets held 12+ months — a 7% gain effectively becomes a 3.5% taxable gain for a top-bracket investor (47% rate) = 1.645% tax, so net after-tax return ≈ 5.35%.
Dividends: Fully franked dividends carry a 30% franking credit. For investors on ≤30% tax rate, dividends are effectively tax-free. For investors on 45%+, there’s still some additional tax after credits.
Inside super (accumulation): Earnings taxed at 15%. CGT at 10% (after 12 months). Returns compound more efficiently inside super.
Useful Online Tools
Several ASIC-approved and third-party tools allow interactive modelling:
- ASIC MoneySmart Compound Interest Calculator: moneysmart.gov.au — simple, reliable
- Vanguard Retirement Income Calculator: vanguard.com.au
- Sorted (NZ-based but useful): sorted.org.nz
- Portfolio Visualizer: portfoliovisualizer.com — advanced, US-centric but useful for concepts
Common Return Assumptions for Australian Modelling
| Asset class | Historical average return (approx.) | Source context |
|---|---|---|
| Australian shares (ASX 200) | 9–10% nominal (incl. dividends) | Long-run MSCI / ASX data |
| Global shares (MSCI World) | 8–9% nominal (AUD) | Long-run data |
| Australian bonds | 4–6% nominal | Varies by period/rate environment |
| Cash/term deposits | 2–5% nominal | Varies with RBA cash rate |
| Balanced fund (60/40) | 6–8% nominal | Common proxy |
Always note that past performance is not a reliable indicator of future performance. Investment returns will vary — actual results may be higher or lower.
Related Calculators
- Compound Interest Calculator Australia
- DCA Calculator Australia
- Retirement Calculator Australia
- Investment Calculators hub
Frequently Asked Questions
What is a realistic investment return assumption for Australia? A commonly used long-term assumption for a diversified Australian growth portfolio is 7–8% nominal per annum — roughly in line with historical ASX and global share market returns after fees but before inflation. Real returns (after ~3% inflation) of 4–5% are a more conservative planning assumption. Past performance is not a reliable indicator of future performance.
How do I calculate my investment return? For a simple lump sum: $FV = PV \times (1+r)^n$. For regular contributions, use the annuity formula or an online calculator. Adjust for fees (subtract MER from return), inflation (subtract CPI from nominal return), and tax (apply your effective tax rate on income and CGT).
How much does $10,000 grow in 10 years in Australia? At 7% annual return: $10,000 × (1.07)^10 = $19,672. At 5%: $16,289. At 10%: $25,937. These are nominal (before inflation) figures. After 3% inflation, real purchasing power at 7% = approximately $14,600 in today’s dollars.
This article provides general financial information only. Calculator results are illustrative — actual investment returns will vary. For advice tailored to your situation, speak with a licensed financial adviser through the ASIC financial advisers register or MoneySmart.