Double your money faster. Interactive calculator, Rule of 72, tables from 4-12%, and the exact return you need to double in 5, 10, or 15 years.
9 min read · Published 2026-03-17 · Updated 2026-07-24
The Rule of 72 is a mental-math shortcut for compound growth: divide 72 by your annual return rate to estimate the years it takes to double your money. At 8%, 72 ÷ 8 = 9 years. It's derived from the natural logarithm of 2 and is most accurate between 4% and 12%.
The doubling time is the same for any starting amount — only the return rate matters. At 7%, $1,000 doubles to $2,000 in about 10.3 years. At 10%, in about 7.3 years.
Approximately 10.3 years. The Rule of 72 estimate (72 ÷ 7 = 10.29) is nearly exact for this rate. Every $10,000 you invest at 7% becomes $20,000 in a decade.
Approximately 7.3 years. Using the Rule of 72: 72 ÷ 10 = 7.2, which is within a month of the exact answer. This is the historical S&P 500 nominal average.
You'd need roughly a 14.4% annual return (72 ÷ 5 = 14.4). That's above the long-term stock-market average and typically requires concentrated growth stocks, leveraged real estate, or business ownership — all with meaningfully higher risk.
About 7.2% annually. That's precisely why a broad S&P 500 index fund is such a common recommendation — its long-term average return of ~10% doubles money faster than the 10-year mark, and its inflation-adjusted return of ~7% doubles it right at 10.
Yes. If your return is 7% and inflation is 3%, your real purchasing power grows at about 4% — so real doubling takes ~18 years, not 10. Always compare against inflation for long-term planning.
Very. For a 7% return, the rule says 10.3 years; the exact answer is 10.24 years. Between 4% and 12%, the rule is accurate to within 0.1 years — more than precise enough for financial planning.