These two terms come up constantly in finance, and mixing them up can lead to real misunderstandings about what a loan or investment will actually cost or earn. Here's the difference, in plain terms.
Interest is calculated only on the original principal, for the entire duration — it never compounds. The formula is straightforward:
Simple Interest = Principal × Rate × Time
Each year, you pay (or earn) the same amount of interest, because it's always calculated on the same original sum.
Interest is calculated on the principal plus any interest already accumulated — meaning interest itself starts earning interest over time. This is why compound growth accelerates the longer it continues.
| Year | Simple Interest (₹1,00,000 @ 10%) | Compound Interest (₹1,00,000 @ 10%, annual) |
|---|---|---|
| 1 | ₹10,000 | ₹10,000 |
| 2 | ₹10,000 | ₹11,000 |
| 3 | ₹10,000 | ₹12,100 |
Notice how compound interest keeps growing each year, while simple interest stays flat.
Understanding that loan interest compounds (via the reducing balance method) explains why paying even slightly more than your EMI, or making occasional prepayments, has an outsized effect — you're reducing the base that future interest compounds on, which saves more than the prepaid amount alone would suggest.
The same principle works in your favour when investing. Compound growth is why starting to invest early — even with small amounts — tends to outperform starting later with larger amounts, given enough time for compounding to work.
Our EMI calculator uses the reducing balance (compounding) method that real lenders use, so the numbers you see reflect what you'd actually be charged.
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