Calculate doubling time instantly with the Rule of 72. Enter any interest rate and see years to double your money.
| Time Period | 5% Return | 7% Return | 10% Return |
|---|---|---|---|
| 5 years | $12,834 | $14,176 | $16,453 |
| 10 years | $16,470 | $20,097 | $27,070 |
| 20 years | $27,126 | $40,387 | $73,281 |
| 30 years | $44,677 | $81,165 | $198,374 |
The Rule of 72 is a simple mental math shortcut: divide 72 by your annual interest rate to estimate the years it takes to double an investment. At 6%: 12 years. At 9%: 8 years. At 12%: 6 years.
The rule works in reverse too: if you want to double your money in 8 years, you need a 9% annual return (72 ÷ 8 = 9). This makes it a powerful tool for evaluating investment options quickly.
It also applies to debt: at 18% credit card interest, your debt doubles in just 4 years if you make no payments. And to inflation: at 3% inflation, prices double every 24 years — meaning $1,000 today buys only $500 worth of goods in 2050.
Rule of 72 Applications: Investments (how fast savings grow) · Debt (how fast balances compound) · Inflation (how fast purchasing power erodes)
Very accurate for rates between 2–20%. At 8%, it estimates 9 years vs. the exact 9.01 years. The rule slightly overestimates at high rates (above 20%).
Rule of 69 is more accurate for continuous compounding. Rule of 72 works better for typical annual/monthly compounding. Rule of 70 is a compromise sometimes used for very rough estimates.
Yes. At 3% inflation, divide 72 by 3 = 24 years for prices to double. This is why long-term purchasing power erosion is significant and why investing above the inflation rate matters.