Doubling time calculator
Convert a percentage growth rate to how long it takes to double, or a doubling time to its growth rate.
That's about the same as a 7 % a year investment. It doubles in 10.24 years and grows tenfold in 34.03 years.
What it means
How fast is that growth?
Assumes steady compound growth. Percent rates compound once per period; “per hour” and “per day” rates are continuous.
Every unit
That growth in every unit
Learn
Three things worth knowing
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The rule of 70
Doubling time ≈ 70 ÷ percent per period: 2 % a year doubles in 35 years, 10 % in about 7.
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Pacioli’s rule of 72
Luca Pacioli gave the “rule of 72” for doubling money in 1494; 72 divides evenly by many interest rates.
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Growth adds up fast
Ten doublings is not ten times: it is 1,024 times.
Shortcuts
Popular growth conversions
Background
About doubling time
Anything that grows by a fixed percentage doubles in a fixed time. The exact doubling time is ln 2 ÷ ln(1 + rate); for small rates that is close to 70 ÷ the percentage, the rule of 70.
It works the same for savings at 7 % a year (about 10 years), a population at 1 % (70 years) and E. coli, which can double every 20 minutes.