Rule of 72 Calculator. Years to Double Your Money
How long until your money doubles?
Divide 72 by a yearly return to estimate how many years it takes an investment to double, then compare the shortcut with the exact figure.
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- Educational only
Set the return.
The steady yearly growth rate. The rule works best between about 6% and 10%.
Whole years, from 1 to 60.
The amount you start with. Enter 0 if you only want the doubling time.
The Rule of 72 is a shortcut, not a forecast. Returns are not steady or guaranteed. These are hypothetical assumptions for learning.
Result
How the value climbs toward double.
View the year-by-year table
What the numbers mean.
A quick mental shortcut.
Divide 72 by the yearly return to estimate how many years it takes to double. At 6% that is 12 years, and at 9% it is 8.
Best near 6% to 10%.
The shortcut is closest to the exact answer for moderate returns. At very low or very high rates it drifts, so use the exact figure there.
It works for prices too.
The same arithmetic shows how long prices take to double at a given inflation rate. At 3% inflation, prices double in about 24 years.
About this rule of 72 calculator.
A Rule of 72 calculator estimates how many years it takes an investment to double. Enter a yearly return, the number of years to look ahead and a starting amount. The calculator divides 72 by the return, compares that shortcut with the exact doubling time, and shows how your money grows year by year, including how many doublings fit in your time frame.
The Rule of 72 is a mental shortcut for compounding, the effect of earning returns on earlier returns. See compound interest examples for the idea in action, the glossary entry on compounding, and the CAGR calculator to turn a start and end value into a yearly rate. To see growth after prices rise, use the real return calculator.
How the rule of 72 calculator works in practice.
You expect a steady 8% a year and start with $10,000. You look 30 years ahead.
Years to double, exact: 9.01 (the shortcut is 0.01 years short)
Years to triple, exact: 14.27
Doublings in 30 years: 3.33
Value after 30 years: $100,627 (10.06×)
Return needed to double in 30 years: 2.40% by the rule, 2.34% exact
At other returns the shortcut drifts a little: at 3% the rule says 24.00 years against an exact 23.45, and at 12% it says 6.00 against 6.12. Even so, it is a useful way to feel how long compounding takes. At 5% the money takes about 14 years to double, and $10,000 becomes $43,219 in 30 years. The same sum grows to only $24,273 at 3%, which is why a few points of yearly return matter so much over decades.
How to choose your inputs for the rule of 72 calculator.
Yearly return. The steady yearly growth rate. The rule works best between about 6% and 10%. Use a return after fees for a realistic picture.
Years to project. Whole years, from 1 to 60. This sets the chart, the table and the return needed to double in that time.
Starting amount. The amount you start with. Enter 0 if you only want the doubling time.
How the Rule of 72 calculator works.
The calculator gives two answers side by side. The Rule of 72 divides 72 by the yearly return, and the exact formula uses logarithms. It then grows your starting amount year by year at the same return.
Exact years to double = ln(2) ÷ ln(1 + yearly return)
Value after n years = starting amount × (1 + yearly return)^n
Return needed to double in n years: Rule of 72 = 72 ÷ n, exact = (2^(1 ÷ n) − 1) × 100
The model assumes one steady return every year, with nothing added or withdrawn, and ignores fees, taxes and inflation. Real returns vary from year to year.
Limits of this rule of 72 calculator.
The Rule of 72 assumes one steady return every year, with nothing added or withdrawn. It ignores fees, taxes and inflation, so use an after-fee return if you want a realistic picture, and try the real return calculator to see growth after inflation. Real returns vary from year to year, and a high return is never guaranteed.
Common questions about the rule of 72 calculator.
What is the Rule of 72?
The Rule of 72 is a shortcut for estimating how long an investment takes to double. Divide 72 by the yearly return in percent. At 8% that gives 9 years.
Why 72 and not 70 or 69?
72 divides evenly by many common rates, such as 6, 8, 9 and 12, which makes mental maths easy. The exact constant for continuous compounding is closer to 69.3, and 70 or 69 can fit slightly better at low rates.
How accurate is the Rule of 72?
It is very close at moderate returns. At 8% it is off by about 0.01 years. At 3% it overstates by about half a year, and at 12% it understates by about 0.12 years.
Is the result a forecast?
No. It assumes a steady yearly return with nothing added or taken out. Real returns vary and are never guaranteed.
How do I use the Rule of 72?
Divide 72 by the yearly return as a percentage. The answer is the number of years to double. To go the other way, divide 72 by the number of years to find the return needed.
How long does it take to double money at 7%?
About 10.3 years by the rule (72 ÷ 7). The exact figure is 10.24 years.
Does the Rule of 72 work for inflation?
Yes, the same arithmetic shows how long prices take to double. At 3% inflation, prices double in about 24 years, so money kept as cash loses about half its buying power over that time.
More calculators.
Educational illustration only, not a forecast or personal investment recommendation. The model assumes a steady return and excludes fees, taxes and inflation.
Further learning: Glossary: Compounding · Compound interest examples · Investor.gov: Financial tools and calculators · Research methodology · Financial disclaimer