Rule of 72 Calculator

Use our free Rule of 72 calculator to estimate how long it will take to double your investment at a given annual rate of return, or what interest rate you need to double your money in a specific time frame.

Financial

Calculate

Annual Rate of Return (%)

Desired Doubling Time (years)

years

Principal Amount (optional)

Currency

Formula

The Rule of 72 is a simple mental math formula that estimates how long it takes to double your money at a fixed annual rate of return. Divide 72 by your expected annual return rate to get the approximate number of years.

Years to Double = 72 / Rate, Rate Needed = 72 / Years

Percentage: The percentage value you want to apply

Number: The original number or value

Result: The calculated result

How It Works

1Choose whether to calculate time to double or rate needed.
2If calculating time: enter the annual rate of return.
3If calculating rate: enter the desired doubling time in years.
4Optionally enter a principal amount to see the future value after doubling.

Examples

8% annual return - how long to double?

1.Years to double = 72 / 8 = 9 years
2.$10,000 becomes $20,000 in approximately 9 years at 8%

Result: 9 years

Frequently Asked Questions

The Rule of 72 is a simple formula that estimates how long an investment takes to double: Years = 72 / Annual Rate of Return.

The Rule of 72 is most accurate for rates between 6% and 10%. For very high or low rates, the Rule of 69.3 or 70 may be more precise.

Yes, you can also use it to estimate the effect of inflation (how long until your money halves in purchasing power) or fees on investment growth.

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Rule of 72 Explained

CalculateMe Team

Last updated: 2026-07-15

Frequently Asked Questions

The Rule of 72 is a simple formula that estimates how long an investment takes to double: Years = 72 / Annual Rate of Return.

The Rule of 72 is most accurate for rates between 6% and 10%. For very high or low rates, the Rule of 69.3 or 70 may be more precise.

Yes, you can also use it to estimate the effect of inflation (how long until your money halves in purchasing power) or fees on investment growth.

Rule of 72 Calculator

Formula

How It Works

Examples

8% annual return - how long to double?

Frequently Asked Questions

What is the Rule of 72?

How accurate is the Rule of 72?

Can I use the Rule of 72 for anything else?

Related Calculators

Related Articles

Rule of 72 Calculator

Formula

How It Works

Examples

8% annual return - how long to double?

Frequently Asked Questions

What is the Rule of 72?

How accurate is the Rule of 72?

Can I use the Rule of 72 for anything else?

Related Calculators

Related Articles