What is the Rule of 72?

The Rule of 72 is a simplified formula to estimate how long an investment will take to double in value. Divide 72 by the annual interest rate to get the approximate years to double.

How accurate is the Rule of 72?

The Rule of 72 is most accurate for interest rates between 6% and 10%. For rates outside this range, Rules 69 or 70 may be more accurate. The calculator shows exact calculations alongside rule-based estimates.

What's the difference between Rule of 72, 69, and 70?

Rule of 72 works best for annual compounding at moderate rates. Rule of 69.3 is more accurate for continuous compounding. Rule of 70 is simpler and works well for lower interest rates.

Rule of 72 Calculator

Quickly estimate how long it will take to double your investment using the Rule of 72 and other financial shortcuts. Perfect for rapid mental calculations and investment planning without complex formulas.

What do you want to calculate?

Annual Rate of Return (%)

Years to Double/Triple Investment

Rule to Use:

Compounding Frequency:

Result: -

Exact Calculation: -

Accuracy: -

Rule Used: -

Understanding Investment Doubling Rules

📐 Rule of 72

Time to Double:

Years = 72 ÷ Interest Rate (%)

Required Rate:

Rate (%) = 72 ÷ Years

Best for rates between 6-10%

🔬 Exact Formula

Precise Calculation:

Years = ln(2) ÷ ln(1 + r)

Where:

r = interest rate (decimal)

100% accurate for any rate

When to Use Each Rule

📊 Rule of 72

Standard for annual compounding
Most accurate: 6-10% rates
Easy mental math (72 has many factors)
Traditional finance rule

📈 Rule of 69.3

Best for continuous compounding
More mathematically precise
Derived from ln(2) ≈ 0.693
Used in scientific calculations

📉 Rule of 70

Simpler mental math
Good for lower rates (2-6%)
Often used in economics
GDP and inflation calculations

Practical Examples

💰 Stock Market Investment

Historical S&P 500 average return of ~10% annually:

Rule of 72 72 ÷ 10 = 7.2 years

Exact 7.27 years

$10,000 becomes $20,000

🏦 Savings Account

Current high-yield savings at 4% annually:

Rule of 72 72 ÷ 4 = 18 years

Rule of 70 70 ÷ 4 = 17.5 years

Exact 17.67 years

📈 Inflation Impact

Money losing value at 3% inflation:

Rule of 70 70 ÷ 3 = 23.3 years

Purchasing power Halved in 23 years

$100 worth $50 in today's money

Beyond Doubling: Other Financial Rules

3️⃣ Rule of 114

Time to triple your investment:

Years = 114 ÷ Interest Rate (%)

Example: At 8%, money triples in 14.25 years

4️⃣ Rule of 144

Time to quadruple your investment:

Years = 144 ÷ Interest Rate (%)

Example: At 8%, money quadruples in 18 years

💵 Rule of 110

Stock allocation by age:

Stock % = 110 - Your Age

Example: At age 30, hold 80% stocks

How to Use This Calculator

Choose Calculation

Select time, rate, or tripling calculation

Enter Value

Input your interest rate or time period

Select Rule

Choose which rule or use auto-select

Set Compounding

Match your investment's compounding

Calculate

Get both rule estimate and exact result

💡 Investment Planning Tips

🎯

Use these rules for quick estimates, but verify with exact calculations for important decisions

📊

Remember that actual returns vary - these calculations assume constant rates

💸

Don't forget to account for taxes, which can significantly impact doubling time

📈

Higher risk investments may offer faster doubling but with greater uncertainty

🛡️

Inflation reduces real returns - subtract inflation rate from nominal returns

Rule Accuracy Comparison

Interest Rate	Rule of 72	Rule of 70	Rule of 69.3	Exact Years
2%	36.0 years	35.0 years	34.7 years	35.0 years
4%	18.0 years	17.5 years	17.3 years	17.7 years
6%	12.0 years	11.7 years	11.6 years	11.9 years
8%	9.0 years	8.8 years	8.7 years	9.0 years
10%	7.2 years	7.0 years	6.9 years	7.3 years
12%	6.0 years	5.8 years	5.8 years	6.1 years