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Free Rule of 72 Calculator

Estimate how long money takes to double at a given rate, or the rate needed.

The rule of 72 divides 72 by the annual return to approximate the years to double, and the tool compares it with the exact figure from logarithms. It also gives the rule of 114 for tripling and the return needed to double within your target years.

How to use the Rule of 72 Calculator

  1. Enter your starting amount, regular contribution, expected return and time period.
  2. Read the end value and the split between money you put in and growth.
  3. Try a lower return as well as a higher one, because real markets are uneven.

About the Rule of 72 Calculator

Estimate how long money takes to double at a given rate, or the rate needed.

Time and consistency do most of the work in saving and investing. Running the numbers shows how small changes in rate, term or contribution add up.

Getting started with the Rule of 72 Calculator

Using the rule of 72 calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.

Tips for better results

The rule works best for rates between about 6 and 10 percent. For quick comparisons, remember that the return is assumed constant and fees and taxes are ignored.

Treat the result as an illustration, not a promise. Returns vary year to year.

Fees and inflation reduce real growth, so consider both when planning.

Privacy and where your data goes

Everything you type into the rule of 72 calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.

Frequently asked questions

Why 72?

It is close to the natural log of 2 times 100 and divides evenly by many common rates, making mental maths easy. The exact result differs slightly, as the tool shows.

Does the rule apply to inflation?

Yes. At 3 percent inflation, prices roughly double in 24 years, meaning purchasing power halves in that time.

Is the rule of 72 calculator free?

Yes. It is free to use with no signup, no watermark and no usage limits.

Is my data private?

Yes. Your inputs are processed in your browser and saved only in its local storage. They are not uploaded to our servers.

Does it work on mobile?

Yes. Zapxa works on phones, tablets and desktops. Use the print button or download a PDF to keep a copy.

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