Rule of 72 Calculator

Estimate how long it will take for your investment to double at a given annual rate of return

Investment Information

Annual Rate of Return (%)

Initial Investment

Currency US Dollar ($) Euro (€) British Pound (£) Japanese Yen (¥) Canadian Dollar (C$) Australian Dollar (A$) Chinese Yuan (¥) Indian Rupee (₹)

Rule of 72 Results

Doubling Time

-

years

Time for investment to double

Doubling Date

-

Approximate date your investment will double

Doubled Amount

-

Final amount after doubling

Doubling Timeline

Period	Years	Date	Amount
Calculate to see timeline

About the Rule of 72

The Rule of 72 is a simple way to estimate how long an investment will take to double, given a fixed annual rate of interest. By dividing 72 by the annual rate of return, investors can get a rough estimate of how many years it will take for the initial investment to double.

Key Benefits

• Quick mental calculation

• Simple to understand

• Useful for comparing investments

• Works well for rates between 6% and 10%

Limitations

• Less accurate for very high or low rates

• Doesn't account for taxes or fees

• Assumes compound interest

• Doesn't consider inflation

This calculator provides estimates only. Investment returns are not guaranteed. Print Results

A Rule of 72 Calculator is a quick mental math tool that estimates how long it will take for an investment to double in value based on a fixed annual rate of return. It’s widely used in finance for its simplicity and practicality.

---

How the Rule of 72 Works

The Formula

$$\text{Years to Double}=\frac{72}{\text{Annual Interest Rate (\%)}}$$

Example:

• Interest Rate: 6% per year

• Years to Double: $\frac{72}{6}=12\text{ years}$

Key Features

✔ Works for compound interest (not simple interest).
✔ Best for rates between 6% and 10% (less accurate for extreme rates).
✔ Can also estimate required rate to double money in a set time.

---

How to Use the Rule of 72

1. Estimating Doubling Time

Interest Rate	Years to Double
3%	24 years
6%	12 years
9%	8 years
12%	6 years

2. Reverse Calculation (Finding Required Rate)

Example:

• Goal: Double money in 8 years.

• Required Rate: $\frac{72}{8}=9\mathrm{\%}$

---

Why the Rule of 72 Matters

✅ Quick mental math – No calculator needed.
✅ Compare investments – Stocks (7-10%) vs. bonds (3-5%).
✅ Financial planning – Estimate retirement or savings growth.

---

Limitations

⚠ Approximation only – Not exact (real math uses logarithms).
⚠ Works best for moderate rates (6-12%).
⚠ Assumes constant returns – Real-world investments fluctuate.

---

Rule of 72 vs. Rule of 70 vs. Rule of 69

Rule	Formula	Best For
Rule of 72	$\frac{72}{r}$	General estimates (6-10% returns)
Rule of 70	$\frac{70}{r}$	Continuous compounding (economics)
Rule of 69	$69.3\mathrm{/}r+0.35$	High precision (math-heavy)

---

Real-World Applications

1. Retirement Planning

   • If your portfolio grows at 7%, it doubles every ~10 years.

   • $100K → $200K in 10 years → $400K in 20 years.

2. Debt Management

   • A 12% APR credit card debt doubles in 6 years if unpaid.

3. Business Growth

   • A company growing at 9% annually doubles in size in 8 years.