Simple Interest vs Compound Interest
What is it?
Simple interest is calculated only on the original principal amount for the entire period. Compound interest is calculated on the principal plus any interest already earned, so the base it's calculated on grows over time.
Why should you care?
The difference seems small in year one but widens significantly over longer periods — knowing which one applies to a loan or investment tells you how fast your money (or debt) will actually grow.
Real-life example
₹1,00,000 at 10% p.a. for 10 years: with simple interest, you earn a flat ₹10,000/year, ending with ₹2,00,000. With compound interest (compounded annually), you end with about ₹2,59,374 — nearly ₹60,000 more, purely because each year's interest also earns interest.
Common mistakes
- Assuming all investment products use compound interest — some fixed-income instruments quote simple interest, so always check the terms.
- Confusing the compounding frequency (annual, monthly, daily) — more frequent compounding produces a slightly higher effective return for the same stated rate.
- Not applying the same lens to loans — a loan compounding monthly costs meaningfully more than one compounding annually at the same headline rate.
₹1,00,000 at 10% p.a. for 10 years
| Method | Final value |
|---|---|
| Simple interest | ₹2,00,000 |
| Compound interest (annual) | ₹2,59,374 |
FAQ
Which do banks use for savings accounts?
Most Indian savings accounts and recurring/fixed deposits use compound interest, typically compounded quarterly, though the exact frequency varies by bank and product.
Which is better for me as a borrower?
Simple interest is better for borrowers since the interest doesn't grow on itself, but most consumer loans (like credit cards) use compound interest, which is why unpaid balances can grow quickly.
Does compounding frequency matter a lot?
It matters more as the rate and time period increase — for short periods and modest rates the difference between annual and monthly compounding is small, but it adds up over decades.
How can I tell which one applies to my investment?
Check the product's terms/factsheet — mutual funds don't pay "interest" in this sense at all (returns come from market value changes), while bonds, FDs, and loans specify their interest calculation method explicitly.
See this concept applied to your own portfolio
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