Rule of 72 Calculator
Calculate how long it takes to double your money using the Rule of 72 with our free calculator. This powerful mental math shortcut helps investors quickly estimate investment growth—simply divide 72 by your expected annual return to find the doubling time.
Rule of 72 Quick Reference
| Annual Return | Years to Double | Example | 2%36 yearsSavings account 4%18 yearsConservative bonds 6%12 yearsBalanced portfolio 8%9 yearsGrowth stocks 10%7.2 yearsS&P 500 historical 12%6 yearsAggressive growth | 15% | 4.8 years | Exceptional performance |
How the Rule of 72 Works
Years to Double = 72 ÷ Annual Interest Rate
For example:
- At 6% return: 72 ÷ 6 = 12 years to double
- At 8% return: 72 ÷ 8 = 9 years to double
- At 10% return: 72 ÷ 10 = 7.2 years to double
Rule of 72 Calculator
``javascript
function ruleOf72(annualRate) {
const yearsToDouble = 72 / annualRate;
const actualYears = Math.log(2) / Math.log(1 + annualRate/100);
// Calculate growth over multiple doublings
const doublings = [1, 2, 3, 4, 5];
const growthTable = doublings.map(d => ({
doublings: d,
years: (yearsToDouble * d).toFixed(1),
multiplier: Math.pow(2, d) + 'x'
}));
return {
yearsToDouble: yearsToDouble.toFixed(1),
actualYears: actualYears.toFixed(2),
accuracy: ((yearsToDouble / actualYears) * 100 - 100).toFixed(1) + '% error',
growthProjection: growthTable
};
}
``
Using Rule of 72 for Other Calculations
The rule works in reverse too: to find the rate needed to double in N years, divide 72 by N. Want to double your money in 10 years? You need 72 ÷ 10 = 7.2% annual returns. The rule also applies to inflation—at 3% inflation, prices double every 24 years.