Why Use This Rule of 72 Calculator
The Rule of 72 is one of the most useful shortcuts in personal finance. It helps you quickly estimate how long your money takes to double at a given rate. This Rule of 72 calculator makes the math instant and precise.
- ✅ Quick Estimates — instantly see how long it takes to double your money.
- ⏱️ Two Modes — calculate doubling time OR find the required rate to double by a specific date.
- 📈 Visual Growth Charts — see your balance grow to 2×, 4×, and beyond.
- 📐 Rule of 72 Formula — understand the math behind the estimate.
- 📜 Calculation History — save, review, and export past results to CSV or Excel.
- 🌍 170+ Currencies — automatically formats results in your local currency.
- 🔒 100% Private — all calculations run locally; your data never leaves your browser.
Rule of 72 Formula
The Rule of 72 formula is simple:
Years to Double ≈ 72 ÷ Annual Rate
For example:
- At 6% return: 72 ÷ 6 = 12 years
- At 8% return: 72 ÷ 8 = 9 years
- At 10% return: 72 ÷ 10 = 7.2 years
Exact Formula (for comparison):
t = ln(2) / ln(1 + r)
Where:
- t = Years to double
- r = Annual rate of return (as a decimal)
- ln = Natural logarithm
The Rule of 72 is most accurate for rates between 6% and 10%. This calculator shows both the Rule of 72 estimate and the exact calculation.
How to Use This Tool
- Select your account currency from the picker in the site header.
- Enter your annual return rate (e.g., 7 for 7%).
- Set a target time (optional) — enter a time in years to find the required rate. Leave at 0 to calculate doubling time.
- Enter a starting amount (optional) — see the final balance when your money doubles.
- The tool updates instantly — you’ll see your time to double, required rate, and final balance.
Frequently Asked Questions
What is the Rule of 72?
The Rule of 72 is a quick formula to estimate how long it takes for an investment to double at a fixed annual rate of return. Divide 72 by the annual rate to get the approximate number of years.
How accurate is the Rule of 72?
The Rule of 72 is most accurate for rates between 6% and 10%. For rates outside this range, the error increases. This calculator shows both the Rule of 72 estimate and the exact calculation.
What is the Rule of 72 formula?
The formula is: Years to Double = 72 ÷ Annual Rate. For example, at 8% return: 72 ÷ 8 = 9 years. The exact formula is: t = ln(2) / ln(1 + r).
Can I use this calculator for any rate?
Yes. Use it for stocks, bonds, savings accounts, or any investment with a fixed annual return rate. The calculator works for any positive rate.
Is my data stored anywhere?
No. All calculations run locally in your browser. History and presets are saved in your browser’s localStorage — nothing is sent to a server.