Learn compound vs simple interest formulas with real numerical examples. Discover monthly vs annual compounding frequency and Rule of 72 growth tricks.
Simple vs Compound Interest
Simple interest is calculated only on the original principal. Compound interest is calculated on the principal AND the accumulated interest — meaning your interest earns interest. To calculate your potential earnings, use our compound interest investment calculator to model compound growth over time. This creates exponential growth that becomes dramatically more powerful over longer time periods.
₹1,00,000 at 10% for 10 years → SI = ₹1,00,000
₹1,00,000 at 10% compounded monthly for 10 years → A = ₹2,70,704
The same ₹1 lakh investment earns ₹1,00,000 with simple interest versus ₹1,70,704 with monthly compound interest — a 70% difference!
Compounding Frequency Matters
| Frequency | ₹1L at 12% for 10 years |
|---|---|
| Annual compounding | ₹3,10,585 |
| Quarterly compounding | ₹3,26,204 |
| Monthly compounding | ₹3,30,039 |
| Daily compounding | ₹3,31,946 |
💡 For most long-term investments, the difference between monthly and daily compounding is small. What matters far more is the interest rate and investment duration.
The Rule of 72
The Rule of 72 is a simple mental math shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money:
- At 6% → doubles in 72 ÷ 6 = 12 years
- At 9% → doubles in 72 ÷ 9 = 8 years
- At 12% → doubles in 72 ÷ 12 = 6 years
- At 18% → doubles in 72 ÷ 18 = 4 years
Why Time Horizon Matters More Than Rate
Consider two investors:
- Investor A invests ₹5,000/month from age 25 to 35 (10 years), then stops. Total invested: ₹6 lakh.
- Investor B invests ₹5,000/month from age 35 to 60 (25 years). Total invested: ₹15 lakh.
At 12% annual return, Investor A ends up with ₹3.5 crore and Investor B with ₹2.1 crore — despite investing 2.5× less money. The 10-year head start makes all the difference.
📈 Calculate compound interest returns — try lump sum and SIP
Open Investment Calculator →📚 External Scientific References & Authoritative Sources
- Investopedia Financial Library — Compounding Growth, Ratio Calculations & Financial Formulas.
- U.S. Securities and Exchange Commission (SEC) — Investor Education & Compound Interest Calculations.
- Reserve Bank of India (RBI) — Banking Regulations, Amortization Standards & Lending Guidelines.
💡 Key Takeaways
Compound interest accelerates wealth accumulation over time. The earlier you start investing and the higher your compounding frequency, the greater your long-term investment growth.