Financial calculator
Rule of 72 Calculator
Enter an annual return rate to see roughly how many years it would take money to double — the Rule of 72 shortcut (72 divided by the rate).
How to use this calculator
At 8% a year, 72 / 8 is about 9 years to double. Enter your own rate; this is a quick approximation, not a precise projection.
Inputs are editable, results update locally in the browser, and outputs are informational estimates based only on the assumptions entered.
How the Rule of 72 works
The Rule of 72 is a mental-math shortcut: divide 72 by an annual percentage rate and you get the approximate number of years for a sum to double at that rate, assuming the gains compound.
It is close to the exact compounding answer for rates in the usual single-digit-to-low-teens range, which is why it is so widely used.
When it is and isn't accurate
The shortcut is an approximation — most accurate near 8% and drifting at very high or very low rates. For precision, use the compound-interest math directly.
The rate you enter is an assumption; the result is a rough estimate, not a forecast of any real investment.
Data notice: Market data may be delayed, incomplete, or unavailable for some securities. Metrics are provided for informational purposes only.
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Calculator notes
- The calculator runs in the browser and keeps the assumptions visible to the reader.
- Inputs are transparent and editable, which makes the assumptions visible to the reader.
- Results are estimates for informational purposes and can be compared with stock and ETF research pages.
Financial disclaimer
This website provides informational content only and is not financial advice. We do not recommend buying or selling securities. Market data may be delayed, incomplete, or inaccurate. Always verify information with official sources before making financial decisions.
FAQ
What is the Rule of 72?
Divide 72 by an annual return rate to approximate the years it takes money to double at that compounding rate. At 6%, that is about 12 years.
How accurate is the Rule of 72?
It is a close approximation for everyday rates (most accurate around 8%) and drifts at extreme rates. For exact figures, use compound-interest math.
Does it predict returns?
No. It only converts a rate you assume into an approximate doubling time; it is not a forecast.