The Core Difference
📐 Simple Interest (SI)
Interest calculated only on the original principal amount.
- • Interest does not earn further interest
- • Linear growth
- • Used in: short-term loans, car loans
📈 Compound Interest (CI)
Interest calculated on principal + previously earned interest.
- • Interest earns interest (exponential growth)
- • Used in: FD, MF, SIP, credit cards, loans
Real-World Comparison: ₹1 Lakh Investment
Principal: ₹1,00,000 | Rate: 8% per annum
| Year | Simple Interest | Compound Interest (Annual) | CI Advantage |
|---|---|---|---|
| 1 | ₹1,08,000 | ₹1,08,000 | Same |
| 3 | ₹1,24,000 | ₹1,25,971 | +₹1,971 |
| 5 | ₹1,40,000 | ₹1,46,933 | +₹6,933 |
| 10 | ₹1,80,000 | ₹2,15,892 | +₹35,892 |
| 20 | ₹2,60,000 | ₹4,66,096 | +₹2,06,096 |
| 30 | ₹3,40,000 | ₹10,06,266 | +₹6,66,266 |
After 30 years: ₹3.4 lakh (Simple Interest) vs ₹10 lakh+ (Compound Interest) — compounding creates ₹6.66 lakh extra from identically invested principal.
Where Each Type Appears in India
Fixed Deposits (FD)
Compound interest (quarterly compounding). Even small additional compounding frequency matters significantly over time.
PPF (Public Provident Fund)
Compound interest, compounded annually. One of India's best long-term wealth creation instruments.
SIP / Mutual Funds
Returns compound over time — why long-term SIPs dramatically outperform short-term ones.
Credit Card Outstanding Balance
Compound interest at 2–4% per MONTH (24–48% per year). The most expensive compound interest for consumers.
Personal Loans from Banks
Reducing balance (compound interest type) — always calculate total interest paid.
Short-term Loans (Payday/NBFC)
Often flat rate (simple interest structure) — but at very high rates that are deceptive.
The Rule of 72
A quick mental shortcut: Divide 72 by the interest rate to estimate how many years it takes to double your money with compound interest. At 8%: 72 ÷ 8 = 9 years to double. At 12% (typical equity mutual fund): 72 ÷ 12 = 6 years. At 4% (savings account): 72 ÷ 4 = 18 years.
Calculate your EMI and interest breakdown precisely with ToolsWallet's free EMI Calculator — see exactly how much interest you pay over the loan tenure.