Rule of 72 Calculator
Estimate how long money takes to double. The rule of 72 divides 72 by the annual rate. The page also shows the exact compound time.
How it is calculated
Rule of 72: years ≈ 72 ÷ rate. Exact: ln(2) ÷ ln(1 + rate/100)
- The rule of 72 is a shortcut. It is close for rates near 8% to 12% and drifts as the rate moves away.
- The exact line is the compound time for an annual rate, with no contributions added along the way.
- The chart compares both formulas from 4% to 24% so the shortcut stays visible.
This is a projection or a description of the numbers you type. It is not financial advice.
A shortcut, shown next to the exact time
Divide 72 by the annual percent and you get a rough number of years for money to double. At 12% the rule says 6 years. The exact compound time is a little longer.
This page shows both, so the rule is not mistaken for a precise forecast. The amount you enter is only there to label what 'double' means in rupees.
Questions
Why is the exact time different from 72 divided by the rate?
72 ÷ rate is an approximation of ln(2) ÷ ln(1 + rate/100). The two meet near everyday rates and separate at very low or very high rates.
Does the amount change the years?
No. Doubling time depends on the rate. The amount only sets the rupee figure for double.
Is this monthly compounding?
The exact figure here is annual compounding. The lumpsum calculator can switch to monthly if you want that comparison.
Can I use this for inflation?
Yes, as a feel for the rate. At 6% inflation the rule says prices double in about 12 years. It is still an approximation.
Does the chart use my amount?
No. The chart compares years at each rate. Your amount is in the summary cards.