Rule of 72 Calculator

The Rule of 72 is a quick mental math trick to estimate how long it will take for your money to double (or reach any multiplier) at a given interest rate.

How It Works

The Formula: Years to Double ≈ 72 / Interest Rate

For example:

• At 8% interest, your money doubles in approximately 72 / 8 = 9 years
• At 6% interest, it takes 72 / 6 = 12 years
• At 12% interest, it only takes 72 / 12 = 6 years

Interactive Calculator

Why It’s Useful

1. Quick Estimates: No calculator needed - just divide 72 by your interest rate
2. Understanding Compound Growth: Visualize exponential growth intuitively
3. Comparing Investments: Quickly see which investment grows faster
4. Long-term Planning: Estimate wealth building over decades

Beyond Doubling

The Rule of 72 can be extended for other multipliers:

• 10x growth: 72 × log(10) / log(2) ≈ 239 / Interest Rate
• Triple (3x): 72 × log(3) / log(2) ≈ 114 / Interest Rate

Real-World Examples

Stock Market (10% average return)

• Money doubles every ~7.2 years
• $10,000 becomes$20,000 in 7 years
• $10,000 becomes$80,000 in 21 years (3 doublings)

High-Yield Savings (5% return)

• Money doubles every ~14.4 years
• $10,000 becomes$20,000 in 14 years

Inflation (3% average)

• Purchasing power halves every ~24 years
• $100 today =$50 purchasing power in 24 years

Limitations

The Rule of 72 is most accurate for:

• Interest rates between 6% and 10%
• Continuous compounding
• Stable, consistent returns

For very high or very low rates, the exact formula is more accurate (shown in the calculator above).