Rule of 72 Calculator | How Long to Double Money

Q: What does the Rule of 72 tell me?

It gives a quick estimate of how many years it takes to double an investment at a fixed annual return. It can also work backwards to estimate the annual interest rate needed to double in a chosen number of years.

Q: When should I use this calculator?

Use it when you want a fast answer to questions like how long to double money , what annual return is needed to double , or how different rates compare over time.

Rule of 72 calculator: estimate how long it takes an investment to double at a fixed annual return, or find the annual return needed to double in a given number of years.

Use this Rule of 72 calculator to estimate how long it takes an investment to double at a fixed annual rate of return, or to find the annual interest rate needed to double in a chosen number of years.

This calculator is a fast shortcut for common investment questions like how long to double money and what rate is needed to double an investment. Enter either the annual return or the target doubling time, then let the calculator solve the missing value.

Rule of 72 formulas

\begin{align} \text{Annual interest rate} &= \frac{72}{\text{Time to double}} \end{align}

\begin{align} \text{Time to double} &= \frac{72}{\text{Annual interest rate}} \end{align}

Initial Data

Annual interest rate

Time to double

Years

Result

Annual interest rate (%)

Time to double

Years

The Rule of 72 estimates how long it takes an investment to double at a fixed annual rate of return.

Rule of 72 FAQ

What does the Rule of 72 tell me?
It gives a quick estimate of how many years it takes to double an investment at a fixed annual return. It can also work backwards to estimate the annual interest rate needed to double in a chosen number of years.

How accurate is the Rule of 72?
It is an approximation, not an exact compound-interest formula. It works best for rates that are not too far from common long-term returns, but it is still very useful for fast mental checks.

When should I use this calculator?
Use it when you want a fast answer to questions like how long to double money, what annual return is needed to double, or how different rates compare over time.

Is the Rule of 72 the same as compound interest?
No. The Rule of 72 is a shortcut built on compound growth. It gives a practical estimate, while exact doubling time comes from the full compound-interest calculation.

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Rule of 72 formulas

Initial Data

Result

See also:

Rule of 72 FAQ