Rule of 72 Calculator

Use the Rule of 72 to instantly calculate how long it takes to double your money at any interest rate, or what return you need to double in a given time.

Rule of 72 Calculator

Instantly calculate how long it takes to double your money

Annual return / interest rate 12%
%
Initial investment Rs 1,00,000
Rs
Years to double
---
Rule of 72
Doubled amount
---
after doubling
Rate needed to double in 10 yrs
7.2%
Rule of 72
At 6% (FD) — doubles in12 years
At 8% (PPF/SSY) — doubles in9 years
At 12% (equity) — doubles in6 years
At 6% inflation — money halves in12 years
Your rate (%) — doubles in---

Rule of 72 is an approximation. Exact doubling time = ln(2)/ln(1+r).

Money growth over time (multiple doublings)
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ThriftRupee Insight

The Rule of 72 is the most powerful mental math tool in personal finance. At 6% FD returns, your money doubles in 12 years. At 12% equity returns, it doubles in 6 years. Inflation at 6% halves your purchasing power in 12 years. This is why beating inflation is non-negotiable -- a savings account at 3.5% doubles your nominal money in 21 years, but inflation has already halved its purchasing power in 12.

Rule of 72 Calculator India

The Rule of 72 tells you how long it takes for an investment to double. Divide 72 by your annual return rate to get the approximate years to doubling. Compare FD, PPF, and equity returns side-by-side.

Frequently asked questions

What is the Rule of 72?▼
The Rule of 72 is a simple formula: Years to double = 72 / Annual interest rate. At 9% return, money doubles in 72/9 = 8 years. At 12%, it doubles in 6 years. It works in reverse too: to double money in 10 years, you need 72/10 = 7.2% annual return. It is an approximation but highly accurate for rates between 6-10%.
How does the Rule of 72 apply to inflation?▼
Use it to understand purchasing power loss. At 6% inflation, prices double in 12 years -- meaning Rs 1 lakh today buys only Rs 50,000 worth of goods in 12 years. At 7% inflation (realistic for healthcare), purchasing power halves in just 10 years. This is why your investments must return significantly more than inflation.
Is Rule of 72 accurate?▼
It is highly accurate for rates between 6-10%. For precision, use Rule of 69.3 (or just ln(2)/rate). The actual doubling time at 12% is 72/12 = 6 years (Rule of 72) vs the exact 5.95 years -- close enough for planning. For rates above 15% or below 3%, the approximation becomes less accurate.

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