Rule of 72 Calculator

Rate → time — enter your expected annual return to see how many years until your money doubles.
Time → rate — enter a target number of years to see what return you need.

Frequently Asked Questions

Why 72?

72 is convenient because it divides evenly into many rates (8, 9, 12, 18). It comes from the natural log of 2 (≈0.693) combined with percentage math.

How accurate is it?

Very accurate for rates between 6% and 10%. For rates far outside that range, the Rule of 71 or 73 is slightly more precise.

Does it work for inflation too?

Yes — divide 72 by the inflation rate to see how long before your money's purchasing power halves.

Is it compound or simple interest?

It assumes compound interest, which is how investments and savings accounts typically work.

Your investment earns 8% per year:

How to Use This Calculator