Quickly estimate how long it takes for your investment to double, or what rate you need to double in a specific time.
Common rates: 4% (bonds), 7% (stocks), 10%+ (high growth)
Used to show projected growth values
Years to Double = 72 / Interest Rate
This mental math shortcut is accurate for rates between 6-10%.
Your Money Will Double In
10.3 years
Exact calculation: 10.24 years (99.6% accurate)
Starting Amount
$10,000
After 1 Doubling
$20,000
After 2 Doublings
$40,000
~21 years
| Interest Rate | Rule of 72 | Exact Time | Accuracy | Value After |
|---|---|---|---|---|
| 2% | 36.0 years | 35.00 years | 97.2% | $20,000 |
| 4% | 18.0 years | 17.67 years | 98.1% | $20,000 |
| 6% | 12.0 years | 11.90 years | 99.1% | $20,000 |
| 8% | 9.0 years | 9.01 years | 99.9% | $20,000 |
| 10% | 7.2 years | 7.27 years | 99.0% | $20,000 |
| 12% | 6.0 years | 6.12 years | 98.1% | $20,000 |
The Rule of 72 is a simple mental math formula to estimate how long an investment will take to double at a fixed annual rate of return. Simply divide 72 by the interest rate to get the approximate years.
The rule is most accurate for interest rates between 6% and 10%. At these rates, it is within 1% of the exact calculation. For very low or very high rates, consider using the Rule of 69.3 (more accurate) or Rule of 70 (easier math).
Rule of 70: Easier math, slightly less accurate. Rule of 69.3: Most mathematically accurate, but harder to calculate mentally.