← All calculators

Rule of 72 Calculator

Compare a quick doubling-time estimate with the exact compound-growth formula.

Enter your assumptions

Change a number. Your estimate updates automatically.

A mathematical shortcut compared with exact constant growth.

Your estimated future balance
—

Projection over time

Constant-rate illustration. Taxes and fees are excluded. Returns can vary or be negative; this is not a guaranteed outcome.

View yearly breakdown
Year-end projections (rounded for display)

How this tool works

Approximate doubling time = 72 ÷ annual percentage return. Exact doubling time = ln(2) ÷ ln(1 + r), where r is the return as a decimal.

Try an example

At 7%, the shortcut gives about 10.29 years. The exact constant-growth result is about 10.24 years.

Questions & assumptions

Can I use a zero or negative rate?

No. A balance does not double through constant growth at a zero or negative rate without deposits. This tool assumes a positive return and no contributions or withdrawals.

Can I export the calculation?

Yes. Download CSV includes inputs and projections. You can also print the results.

Explore more calculators →