Doubling Time Calculator
Find how long an investment takes to double.
Results update as you type.
How it works
How long does it take for money to double at a given rate of return? This calculator gives the exact answer. You enter the annual growth rate, and it returns the precise number of years for an investment to double through compounding. The formula uses natural logarithms: the log of 2 divided by the log of one plus the rate. This is the exact version of the well-known Rule of 72, a mental shortcut that estimates doubling time by dividing 72 by the percentage rate. The Rule of 72 is handy for quick estimates, giving 12 years at 6 percent, but this calculator computes the true figure, about 11.9 years at 6 percent, using the actual math. Doubling time is a powerful way to grasp the effect of compounding and of different rates of return: a small difference in rate has a large effect on how fast wealth grows. At 3 percent money doubles in about 23 years, at 6 percent in about 12, and at 12 percent in only 6, so higher returns compound dramatically faster. The concept applies beyond investing to anything that grows at a constant percentage rate, including populations, inflation eroding purchasing power, and debt. Understanding doubling time helps investors set expectations, compare opportunities, and appreciate why starting early matters so much. Enter the annual growth rate to compute the exact doubling time.
Years = ln(2) / ln(1 + rate)
The exact doubling time is the natural logarithm of 2 divided by the natural logarithm of one plus the growth rate. Unlike the Rule of 72, which is a quick approximation, this logarithmic formula gives the precise number of years for a quantity to double at a constant compounding rate.
Source:Compound growth
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter annual growth rate.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
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Frequently asked questions
How do you calculate doubling time?
Divide the natural logarithm of 2 by the natural logarithm of one plus the growth rate expressed as a decimal. At 6 percent that is ln(2) divided by ln(1.06), about 11.9 years. This gives the exact time for a quantity to double at a constant compounding rate, which the calculator computes for you.
How does this relate to the Rule of 72?
The Rule of 72 is a quick approximation: divide 72 by the percentage rate to estimate doubling years, giving 12 years at 6 percent. This calculator uses the exact logarithmic formula, giving about 11.9 years. The Rule of 72 is close for typical rates but the logarithmic method is precise, especially at very high or low rates.
Why does doubling time matter?
Doubling time makes the power of compounding and the impact of different return rates intuitive. A higher rate doubles money far faster, so small differences in return compound into large differences in wealth over time. It also shows why investing early is so valuable, since more doublings can occur before you need the money.
Does a higher rate double money much faster?
Yes, dramatically. Money doubles in about 23 years at 3 percent, 12 years at 6 percent, and just 6 years at 12 percent. Because doubling time is inversely related to the rate, doubling the return roughly halves the doubling time, which is why even a few extra percentage points of return matter enormously over decades.
Can this apply to things other than investing?
Yes. Any quantity growing at a constant percentage rate has a doubling time, so the formula applies to population growth, inflation eroding the value of money, compound debt, bacterial growth, and more. Wherever something grows by a fixed percentage each period, this calculator tells you how long it takes to double.