💰 Rule of 72 Calculator
Calculate time to double investment
How to Use This Calculator
Enter Annual Interest Rate
Input the annual interest rate (as a percentage). This is the rate at which your investment will grow each year. For example, enter 7 for 7%.
Click Calculate
Press the "Calculate" button to see how long it takes for your investment to double at the given interest rate.
Review Doubling Time
See the number of years it will take for your investment to double in value. Use this to understand the power of compound interest and plan your investments.
Formula
Years to Double = 72 ÷ Interest Rate
Where:
• Interest Rate = Annual interest rate (as percentage)
• Rule of 72 = Quick approximation formula
Example Calculation:
If interest rate 7%:
• Years to double = 72 ÷ 7 = ~10.3 years
• This means $10,000 at 7% becomes ~$20,000 in about 10.3 years
• At 8%, it doubles in 9 years (72 ÷ 8 = 9)
• At 6%, it doubles in 12 years (72 ÷ 6 = 12)
About Rule of 72 Calculator
The Rule of 72 calculator estimates how long it takes for an investment to double in value at a given annual interest rate using a simple formula: 72 divided by the interest rate. The Rule of 72 is a quick mental math approximation that's easy to remember and useful for understanding the power of compound interest. While it's an approximation (not exact), it's very close for interest rates between 6% and 10%. This calculator helps you quickly estimate how long your investments will take to double, which is useful for financial planning and understanding compound interest.
When to Use This Calculator
- Quick Estimates: Quickly estimate doubling time for investments
- Compound Interest: Understand power of compound interest
- Investment Planning: Plan investment goals and timelines
- Financial Education: Learn about compound interest
Understanding the Rule of 72
- Quick Approximation: Simple formula for doubling time
- Compound Interest: Works for compound interest scenarios
- Accuracy: Most accurate for rates 6-10%
- Easy to Remember: Just divide 72 by the interest rate
Why Use Our Calculator?
- ✅ Quick Calculation: Instantly see doubling time
- ✅ Investment Planning: Plan investment timelines
- ✅ Compound Interest: Understand compound interest power
- ✅ Financial Education: Learn about investment growth
- ✅ 100% Free: No registration or payment required
Frequently Asked Questions
What is the Rule of 72?
The Rule of 72 is a simple formula to estimate how long it takes for an investment to double in value: divide 72 by the annual interest rate. For example, at 7% interest, it takes about 10.3 years to double (72 ÷ 7 = 10.3). The rule works well for interest rates between 6% and 10% and is a quick way to understand the power of compound interest.
How accurate is the Rule of 72?
The Rule of 72 is an approximation that's most accurate for interest rates between 6% and 10%. At these rates, it's typically within 1-2% of the actual doubling time. For rates outside this range, accuracy decreases. The exact formula is: Years = ln(2) / ln(1 + r), but Rule of 72 is close enough for quick estimates.
Why 72?
72 is chosen because it has many divisors (1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72), making mental math easier. The number 72 also happens to be close to 100 × ln(2) ≈ 69.3, which is the mathematical constant for doubling time. For more accuracy, you can use Rule of 69.3 or Rule of 70, but Rule of 72 is easier to remember and calculate mentally.
Can I use the Rule of 72 for different scenarios?
Yes! The Rule of 72 works for any compound interest scenario. You can use it for: investment returns, savings accounts, inflation (to see how long prices take to double), population growth, debt (to see how long debt doubles with interest), and more. It's a versatile rule for understanding exponential growth or decay in many financial contexts.