The Rule of 72 says: divide 72 by your annual return rate to get the approximate years to double. Our calculator uses the exact formula for precise results.
Understanding the Rule of 72 & Compound Growth
What is the Rule of 72?+
The Rule of 72 is a mental math shortcut: divide 72 by your annual return rate to estimate how many years it takes to double your money. At 8% return, money doubles in approximately 72 ÷ 8 = 9 years. At 12%, it doubles in 6 years. The rule is approximate — our calculator uses the exact compound interest formula: A = P(1 + r/n)^(nt).
How long does it take to double ₹1 lakh at 10%?+
At 10% annual return with annual compounding, ₹1 lakh doubles to ₹2 lakh in approximately 7.3 years. With monthly compounding at 10%, it takes slightly less — about 7.1 years. After 20 years at 10%, ₹1 lakh grows to approximately ₹6.7 lakhs.
What is compound interest vs simple interest?+
Simple interest is calculated only on your principal. Compound interest is calculated on both your principal AND your accumulated interest — meaning you earn "interest on interest." Over long periods, the difference is enormous. ₹1 lakh at 10% simple interest for 20 years = ₹3 lakh. At compound interest = ₹6.7 lakh. That's the power of compounding.
How does compounding frequency affect returns?+
The more frequently interest compounds, the faster your money grows. At 10% annual rate: annual compounding gives 10% per year. Monthly compounding gives effectively 10.47% (the Effective Annual Rate). Daily compounding gives 10.52%. The difference seems small, but over 20–30 years it adds up to lakhs on a significant corpus.
Which investments double money fastest in India?+
Based on historical data: Equity mutual funds (12–15% p.a.) double money in 5–6 years. PPF (7.1% p.a.) doubles in about 10 years. Fixed Deposits (6–7%) double in about 10–12 years. NPS (10–12% p.a.) doubles in 6–7 years. Real estate returns vary widely by location. Higher returns come with higher risk — diversification is key.