The fastest mental math tool in investing. Find out exactly how many years it takes to double (2x), triple (3x), or quadruple (4x) your money at any given return rate.
📚 Understand This Calculator
Rule of 72: the only mental math trick every investor needs
You don't need a calculator or a spreadsheet for this one. Just divide 72 by your annual return rate, and you instantly know how many years it takes for your money to double. That's the Rule of 72 — a 500-year-old formula that still works perfectly in 2024.
It's surprisingly powerful. Because when you compare how quickly different investments double, suddenly the difference between 7% and 12% stops looking like "just 5%" and starts looking like an entire decade.
🇮🇳 Real-Life Example
Two neighbours, Savita and Rekha, each have ₹10 lakh and want to leave it untouched as long as possible.
📌 Savita puts it in a savings account (3.5%): 72 ÷ 3.5 = 20.6 years to double → ₹20 lakh after 20 years
📌 Rekha invests in an index fund (12%): 72 ÷ 12 = 6 years to double
After 20 years, Rekha's money has doubled 3+ times: ₹10L → ₹20L (yr 6) → ₹40L (yr 12) → ₹80L (yr 18) → ~₹95L at year 20.
Result: Same ₹10 lakh, same 20 years. Savita has ₹20 lakh. Rekha has ₹95 lakh. No extra work — just the choice of where to park the money.
💡 The Key Insight
The Rule of 72 makes the cost of "safe" low-return investments viscerally clear. People think they're being conservative by choosing FDs and savings accounts. But "safe" at 6% means your money takes 12 years to double — while equity at 12% doubles it in 6. Over 30 years, that "safe" choice can cost you ₹1 crore or more on a ₹10 lakh investment.
⚠️ Common Mistake
Applying Rule of 72 to returns after expenses. If a fund's gross return is 14% but the expense ratio is 1.5%, your net return is 12.5%. Always use the net return for the doubling calculation — the one that actually lands in your pocket.
⚡ Your Annual Return Rate
12%
1%10%20%30%
Or type an exact rate: %
72
Rule of 72 — Money Doubles (2x)
6.0 years
Exact: 6.12 years · Formula: 72 / 12%
114
Rule of 114 — Money Triples (3x)
9.5 years
Exact: 9.69 years · Formula: 114 / 12%
144
Rule of 144 — Money Quadruples (4x)
12.0 years
Exact: 12.25 years · Formula: 144 / 12%
Doubling Time at Common Rates
Annual Return
Asset / Context
Doubles in (Rule of 72)
Exact Years
Frequently Asked Questions
How accurate is the Rule of 72? ▾
The Rule of 72 is accurate to within 1–2% for rates between 6% and 20%. At exactly 12% CAGR, the rule says 6 years (72/12) while the exact answer is log(2)/log(1.12) = 6.12 years. At extreme rates (1% or 50%), the error grows. For precise calculation, use our CAGR Calculator.
Why is 72 used and not 70 or 75? ▾
72 was chosen because it has many divisors (1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, 72), making mental division easy. 72/8% = 9 years, 72/12% = 6 years, 72/9% = 8 years — all whole numbers. The number 70 also works mathematically but is slightly less accurate for common investment return rates.
How can I use Rule of 72 for inflation? ▾
The Rule of 72 works for any exponential growth — including inflation. At 6% inflation, 72/6 = 12 years for prices to double. This means the cost of your child's education or retirement expenses will be twice as high in 12 years. Use this to stress-test whether your investment returns are growing faster than costs.
What is the Rule of 114 and 144? ▾
These are extensions of the Rule of 72. Rule of 114 estimates how long to triple (3x) your money: divide 114 by the annual return rate. Rule of 144 estimates quadrupling (4x): divide 144 by the rate. At 12% CAGR: doubles in 6 years (72/12), triples in 9.5 years (114/12), quadruples in 12 years (144/12).
A 1% higher CAGR can shave 1–2 years off your doubling time. BullWiser's MF Analyser helps you find Direct-plan funds with the best risk-adjusted CAGR.