Rule of 72: The Fast Track to Doubling Your Money in Australia (2025 Guide)

If you’ve ever wondered how quickly your savings or investment could double, you’re not alone. For decades, the Rule of 72 has been a favourite shortcut for investors, advisers, and anyone curious about the magic of compounding. But in Australia’s shifting 2025 financial landscape—where interest rates, inflation, and investment returns are moving targets—understanding this rule is more relevant than ever.

What Exactly Is the Rule of 72?

The Rule of 72 is a simple mental math formula: take the number 72 and divide it by your annual rate of return (as a percentage). The result? The approximate number of years it will take for your money to double.

• Formula: Years to double = 72 / (annual rate of return)

Let’s say you have $10,000 in an investment earning 6% per year. Using the Rule of 72: 72 ÷ 6 = 12. So, it would take roughly 12 years to double your money to $20,000.

It’s not just a party trick—it’s a fast, surprisingly accurate way to gauge the impact of compounding on your wealth, especially when you don’t have a financial calculator handy.

Why the Rule of 72 Matters in Australia Right Now

2025 has already seen plenty of financial curveballs. After the Reserve Bank of Australia’s rate hikes and subsequent stabilisation, the cash rate sits at 4.35%, and term deposit rates hover between 4.5% and 5.2% at major banks. Meanwhile, the ASX 200’s annualised return for the past decade clocks in around 7.9%, though 2024 was a standout year at over 10%.

Here’s why the Rule of 72 is especially handy for Australians today:

• Comparing savings vs. investing: With inflation cooling to 3.1% but still above RBA’s 2-3% target, real returns matter more than ever. The Rule of 72 helps you see through the noise.

• Superannuation growth: The government’s stage three tax cuts and adjustments to concessional cap limits in July 2025 mean Aussies may have more to invest in super, making compounding even more powerful.

• Property market shifts: While capital city housing prices have steadied, rental yields and capital growth rates fluctuate—knowing how long your investment takes to double helps with strategic decisions.

Let’s run some real 2025 examples:

• Term deposit at 5%: 72 ÷ 5 = 14.4 years to double

• ASX 200 ETF at 8%: 72 ÷ 8 = 9 years to double

• Property with 4% net growth: 72 ÷ 4 = 18 years to double

Limitations and Smart Uses of the Rule in 2025

The Rule of 72 is a brilliant shortcut, but it’s not a crystal ball. Here’s what to keep in mind:

• Assumes steady returns: Real-world returns fluctuate. Share markets can surge or dip, and term deposit rates change with RBA policy.

• Works best for 6%-10% returns: The rule is most accurate in this range; outside of it, the estimate becomes less precise.

• Doesn’t account for fees or taxes: Superannuation, managed funds, and even bank interest can be eroded by costs and tax—factor these in for real-world planning.

Despite these caveats, the Rule of 72 is an excellent starting point for:

• Comparing potential investments quickly

• Setting long-term financial goals

• Understanding the impact of compounding for kids’ savings accounts or education funds

• Discussing superannuation growth in plain English with family or colleagues

Putting the Rule of 72 to Work: Real Aussie Scenarios

Imagine two friends, Anna and Josh, both starting with $20,000. Anna chooses a high-yield savings account earning 5%, and Josh invests in a diversified ETF expected to return 8% per year.

• Anna: 72 ÷ 5 = 14.4 years to double to $40,000

• Josh: 72 ÷ 8 = 9 years to double to $40,000

Over 18 years, Anna’s account would reach about $54,000, while Josh’s could surpass $80,000 (not accounting for taxes or fees). This stark difference illustrates the compounding advantage of even a few percentage points in return—a core lesson for every Aussie saver and investor in 2025.

Conclusion: Make Compounding Work for You in 2025

In a world where financial products, rates, and policies evolve rapidly, the Rule of 72 remains a timeless, practical tool. Whether you’re planning for retirement, saving for a home deposit, or teaching your kids about money, this rule helps demystify the path to doubling your wealth. Remember: every percentage point counts, and the earlier you start, the greater the compounding magic.