Rule of 72 Calculator
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. Works for investments, debt, and inflation — a universal compounding shortcut.
📈 Investing💰 Doubling Time ≈ 72 / Annual Rate
Annual interest rate (%)
Target doubling time (years)
Please enter valid values.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Rule of 72 Calculator | Doubling Time ≈ 72 / Annual Rate | years to double |
Step-by-Step Examples
Example 1
S&P 500 Average
7% real annual return.
- 72/7 = 10.3 years to double
- $10,000 → $20,000 → $40,000 → $80,000 in 30 years
✓ Doubles every ~10.3 years
Example 2
High-Yield Savings
5% HYSA rate.
- 72/5 = 14.4 years
- Slower than market but much better than 1% checking
✓ Doubles every 14.4 years
Example 3
Credit Card Debt
24% APR.
- 72/24 = 3 years to double the balance
- $5,000 → $10,000 → $20,000 if unpaid
- Catastrophic compounding — pay it off fast!
✓ Debt doubles every 3 years at 24%!
Real-World Applications
Investment Planning
Compare growth rates to see which doubles money fastest.
Financial Literacy
Instant intuition for compound growth without a calculator.
Debt Awareness
Visualize how fast high-interest debt balloons.
Education
A core shortcut taught in finance courses and CFA prep.
Common Mistakes to Avoid
⚠️
Applying to non-compounding rates
Rule of 72 assumes compound interest. Simple interest takes longer to double.
⚠️
Using nominal instead of real rate
At 7% nominal minus 3% inflation, real return is 4% — doubling purchasing power takes 18 years, not 10.
⚠️
Forgetting it works for inflation too
At 3% inflation, purchasing power halves in 72/3 = 24 years.
Frequently Asked Questions
What is the Rule of 72? ▾
Divide 72 by annual interest rate to estimate doubling time. At 8%, money doubles in ~9 years.
How accurate is it? ▾
Very accurate for rates 6–10%. Small errors at extremes, still excellent for planning.
Rate needed to double in a specific time? ▾
Reverse: rate = 72 ÷ target years. To double in 6 years: 72/6 = 12%.
Does it account for taxes? ▾
No. After-tax returns are lower, so doubling takes longer in taxable accounts.
How does it apply to inflation? ▾
At 3% inflation, purchasing power halves in 24 years — why low-yield savings lose real value.