Savings & Growth
Rule of 72 Calculator
How long does it take to double your money? Apply the rule of 72 to any rate, compare it with the exact doubling time, and see every doubling on a chart.
Years to double (rule of 72)
10.3
years · 72 ÷ the yearly rate
Exact doubling time
10.2
years, compounding yearly
Rule of 70
10.0
years
Final value
$76,123
after 30 years
Growth multiple
7.6×
By the rule of 72, money growing at 7.0% a year doubles in about 10 years and 3 months.
The exact doubling time is 10 years and 3 months.
The shortcut is closest for rates around 8%, so it is a good guide here.
Over 30 years, $10,000 would grow to $76,123. To double in exactly 30 years would take 2.34% a year.
The rule works for anything that compounds: at 7.0% inflation, prices double, and the buying power of cash halves, in about 10 years and 3 months.
Your numbers
Your money, doubling after doubling
The doublings come at a steady pace, but each one adds more money than the last: that is compounding.
How the rate changes the doubling time
Exact doubling times. A few points of return, or of fees, change how many doublings fit in a working life.
At 4% a year
17.7
years to double
At 7% a year
10.2
years to double
At 10% a year
7.3
years to double
The rule of 72 formula
Years to double ≈ 72 ÷ yearly rate (in %)
The exact doubling time for growth compounded once a year is ln 2 ÷ ln(1 + r), where r is the yearly rate as a decimal. For small rates, ln(1 + r) is close to r, so the doubling time is close to 69 ÷ the rate in percent (100 × ln 2); rounding up to 72 corrects for yearly compounding at typical rates and makes the division easy in your head.
Why the rule of 72 works
Compounding is hard to picture: a 7% return does not sound very different from 5%. Doubling times make the difference concrete. At 5%, money doubles about every 14 years; at 7%, about every 10. Over a 40-year working life, that is fewer than three doublings against almost four, and the final amount is roughly twice as large.
The rule is old. It appears in Luca Pacioli’s Summa de arithmetica, published in 1494, as a way to estimate how long an investment takes to double. It has lasted because 72 divides cleanly by 2, 3, 4, 6, 8, 9 and 12, so the arithmetic is easy for the rates people actually meet.
Use the rate you really earn. Fees, taxes and inflation all slow the doublings down. To see the real growth of savings with regular deposits, use the compound interest calculator; to measure the yearly rate an investment actually delivered, use the CAGR calculator.
Rule of 72 FAQ
What is the rule of 72?+
A mental shortcut for compound growth: divide 72 by the yearly rate in percent to get roughly how many years it takes to double. At 6% a year, money doubles in about 72 ÷ 6 = 12 years. It works the other way too: to double in 8 years, you need about 72 ÷ 8 = 9% a year.
How accurate is the rule of 72?+
Very, for everyday rates. It is almost exact around 8%: the rule says 9 years and the exact answer is 9 years too. At 2% it says 36 years against an exact 35; at 20% it says 3 years and 7 months against 3 years and 10 months. The calculator shows both side by side.
Should I use 72, 70 or 69?+
72 is the most accurate for typical investment returns of about 6% to 10%, and it divides evenly by many numbers. 70 is closer for low rates, which is why it is often used for inflation and economic growth. 69 is the version for continuous compounding, used in finance textbooks.
Does the rule of 72 work for debt and inflation?+
Yes, for anything that compounds. A credit card balance at 24% a year doubles in about 3 years if nothing is repaid. At 3% inflation, prices double in about 24 years, which also means cash loses half its buying power over that time.
Does it account for fees and taxes?+
Only through the rate you enter. Use the return you keep after fees and taxes: a fund returning 7% with a 1% yearly fee grows at about 6%, which stretches the doubling time from about 10 years to 12.
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Educational tool, not advice. This calculator illustrates a standard formula using the numbers you enter. It does not account for your full financial picture, taxes, or local market conditions, and it is not a recommendation to buy, sell, or hold any asset. Speak with a licensed professional before making investment decisions.
See our full disclaimer and how we calculate.
Last reviewed 2026-11-10 by the Yield Analyst team