The Mental Math of Doubling
To use the Rule of 72, simply divide 72 by your expected annual interest rate. The result is the approximate number of years it will take for your investment to double.
Examples:
- At **6%** interest: 72 ÷ 6 = **12 years** to double.
- At **8%** interest: 72 ÷ 8 = **9 years** to double.
- At **12%** interest: 72 ÷ 12 = **6 years** to double.
While not perfectly precise, the Rule of 72 is remarkably accurate for interest rates in the 5% to 20% range. It's a powerful tool for visualizing the difference a few percentage points can make over a lifetime.