The Rule of 72: how fast will your money double?
Want to know how long it takes to double your money? Divide 72 by your yearly rate of return. That's it.
Key points
- Years to double ≈ 72 ÷ yearly rate.
- At 8%, money doubles in about 9 years.
- It also works in reverse: you can find the rate you need to double by a certain time.
How it works
Say your money grows 6% a year. 72 ÷ 6 = 12. So it takes about 12 years to double.
Want to double your money in 8 years? 72 ÷ 8 = 9. You'd need about 9% a year.
Quick table
| Yearly rate | Rule of 72 | Exact answer |
|---|---|---|
| 4% | 18 years | 17.7 years |
| 6% | 12 years | 11.9 years |
| 8% | 9 years | 9.0 years |
| 10% | 7.2 years | 7.3 years |
| 12% | 6 years | 6.1 years |
The rule is very close for normal rates. That's why people use it to do quick math in their heads.
Doubling adds up fast
At 10%, money doubles about every 7 years. So $10,000 could become:
- $20,000 in about 7 years
- $40,000 in about 14 years
- $80,000 in about 21 years
- $160,000 in about 28 years
That's why starting at 25 instead of 35 can mean more than double the money by retirement. You get one or two extra "doubles."
Savings vs investing
The average savings account paid about 0.37% in September 2026. At that rate, 72 ÷ 0.37 means about 195 years to double. A high-yield account at 3.5% doubles in about 21 years. Stocks have averaged around 10% a year over long periods, which doubles in about 7 years. But stocks can drop along the way.
It works for costs too
Prices rising 3% a year double in about 24 years. So something that costs $50,000 a year today could cost about $100,000 in 24 years. Keep that in mind when you plan for retirement.
Credit card warning
A card charging 24% doubles what you owe in about 3 years if you don't pay it down. Paying off high-interest debt is often the best "investment" you can make.
See how many times your money could double before you retire.
Find your Freedom DayQuick answers
What is the Rule of 72?
It's a shortcut to estimate how long it takes to double your money. Divide 72 by your yearly rate of return.
How accurate is the Rule of 72?
It's very close for rates between about 4% and 12%. For very high or very low rates, it's less exact.
How long does it take to double money at 7%?
About 10 years, since 72 ÷ 7 is about 10.3.
Does the Rule of 72 work for inflation?
Yes. Divide 72 by the inflation rate to see how long it takes prices to double.
Sources
Keep learning
This article is for learning only. It is not financial, tax or legal advice. Example returns are not promises. Talk to a licensed professional about your own situation.