Rule of 69 Calculator (Continuous Doubling)

Verified formula Updated Jun 2026 Private — runs on your device

Verified formula Private

Time to double

8.66

For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.

How to use the Rule of 69 Calculator (Continuous Doubling)

The Rule of 69 Calculator (Continuous Doubling) works out your time to double in an instant. Enter growth rate per period and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.

Enter the growth rate per period.
Read off your time to double — the calculator updates automatically, with no button to press.

Formula

The Rule of 69 Calculator (Continuous Doubling) uses the formula:

Time to double = 69.3 ÷ Growth rate per period

Worked example

For example, with growth rate per period of 8%, the time to double is 8.66.

Inputs used
Growth rate per period	8%

Results
Time to double	8.66

Results are estimates for educational use, not professional advice.

Frequently asked questions

It estimates doubling time for continuous compounding: divide 69.3 by the rate. At 8%, money doubles in about 8.66 years.

The rule of 72 suits periodic compounding; the rule of 69 (or 69.3) is more accurate for continuous compounding.

It comes from the natural logarithm of 2, about 0.693, scaled to a percentage rate.

For continuously compounded growth, common in finance theory and some interest calculations.

The Rule of 69 Calculator (Continuous Doubling) uses the formula: Time to double = 69.3 ÷ Growth rate per period. For example, with growth rate per period of 8%, the time to double is 8.66.

Enter the growth rate per period. Read off your time to double — the calculator updates automatically, with no button to press.