Rule of 72 Calculator
Instantly estimate how long it takes your money to double at any return.
At 8%, money doubles in 9 years (72 ÷ 8). At 12%, in 6 years. The Rule of 72 is the fastest mental check in finance — use it to sanity-check every ‘double your money’ scheme you’re offered.
How to use the rule of 72 calculator
- Enter the annual return rate.
- See years needed to double.
- Or flip it: enter years, get the rate needed.
Rule of 72 Calculator — FAQs
How does the rule of 72 work?
Divide 72 by the annual rate to get approximate doubling years. It’s derived from compound-interest math and accurate within ~1% for rates between 4–15%.
Why 72 and not 70 or 100?
72 has many divisors (2,3,4,6,8,9,12), making mental math easy, and it closely approximates ln(2) in the compound formula.
Can I use it for inflation?
Yes — at 6% inflation, prices double in 12 years. That’s why ₹1 crore today won’t feel like ₹1 crore in 12 years.
Is it exact?
Approximate but close. For precise figures use the compound interest calculator; for quick decisions, 72 is plenty.
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