InvestingMay 14, 2026• 5 min read
The Rule of 72 Explained: How to Calculate When Your Money Will Double
# The Rule of 72 Explained: How to Calculate When Your Money Will Double
What if you could estimate how long it takes to double your money — in your head, in about five seconds? That's exactly what the Rule of 72 does. It's one of the oldest shortcuts in finance.
What Is the Rule of 72?
The Rule of 72 is a mental math shortcut that tells you approximately how many years it will take for an investment to double in value, given a fixed annual rate of return.
The formula: Years to double = 72 ÷ Annual interest rate
How to Use the Rule of 72 — Step by Step
1. Identify your rate of return. E.g., 6%.
2. Divide 72 by that rate. 72 ÷ 6 = 12.
3. Interpret the result. It will take approximately 12 years for your money to double.
Rule of 72 by the Numbers
| Interest Rate | Years to Double |
|---|---|
| 2% | 36 years |
| 4% | 18 years |
| 6% | 12 years |
| 8% | 9 years |
| 12% | 6 years |
Ready to try it yourself?
Use our free Rule of 72 Calculator to apply what you have learned.
Open Rule of 72 Calculator →Frequently Asked Questions
It is highly accurate for interest rates between 6% and 10%.
Yes, it can estimate how long it takes for the purchasing power of money to be cut in half.
Use the "Rule of 114" for tripling or the "Rule of 144" for quadrupling.
The rule is designed for annual rates, but you can use it for any period as long as the rate and result are in the same time units.