Rule of 72 Calculator
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
The Rule of 72
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 |
What is the Rule of 72?
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.
When is it Most Accurate?
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).
Practical Applications
- Estimate investment growth without a calculator
- Compare different investment options quickly
- Understand the impact of fees on long-term returns
- Calculate how inflation erodes purchasing power
Related Rules
Rule of 70: Easier math, slightly less accurate. Rule of 69.3: Most mathematically accurate, but harder to calculate mentally.
Explore More Tools
Discover other calculators in Investing & Retirement to help with your financial planning