Simple vs Compound
Key Takeaway
Simple interest charges interest only on the principal, while compound interest charges interest on principal plus accumulated interest. Over 20 years, compound interest at 10% earns 3.7x more than simple interest.
Divergence of Simple vs. Compound Interest
What to do next
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Linear vs. Exponential Wealth
Simple interest only pays you interest on your original deposit. Compound interest pays you interest on your original deposit PLUS interest on all the previous interest you've earned. It is the difference between walking up a staircase (linear) and taking an elevator that accelerates as it goes up (exponential).
The 30-Year Race: Fixed Deposits vs. Equities
**The Simple Interest Path (e.g., Some specific Bonds at 10%):**
Every year, you earn exactly ₹10,000.
- Year 1: You make ₹10,000.
- Year 30: You make ₹10,000.
After 30 years, you've earned ₹3 Lakhs in interest. Total value = **₹4 Lakhs**.
**The Compound Interest Path (e.g., Equity Mutual Fund at 10%):**
- Year 1: You earn ₹10,000. (Your corpus is now ₹1.10L)
- Year 2: You earn 10% on ₹1.10L, which is ₹11,000.
- Year 30: Because the interest keeps stacking on top of previous interest, in your 30th year alone, your portfolio generates ₹1.58 Lakhs in interest,more than your entire initial investment!
After 30 years, your Total value = **₹17.44 Lakhs**.
By choosing compounding over simple interest, the same amount of money at the exact same rate of return generated over **4x more wealth**. Never withdraw the interest/dividends from your investments unless you absolutely need them; let them compound!
Simple vs Compound Interest: The Difference That Makes Millionaires
In school, we learned both simple and compound interest. Most of us forgot compound interest mattered. The banks, insurance companies, and smart investors did not.
Simple interest pays you the same interest amount every period, calculated only on the original principal. ₹1 lakh at 10% simple interest for 20 years = ₹3 lakhs. Compound interest pays you interest on the interest, so your interest base grows every period. ₹1 lakh at 10% compound interest for 20 years = ₹6.73 lakhs , more than double the simple interest outcome.
Over 30 years, the gap becomes almost mythological: ₹1 lakh at 10% simple = ₹4 lakhs. At 10% compound = ₹17.45 lakhs. The same money. The same rate. The same time. Just a different mathematical rule changes the outcome by 4x.
In the real world: FDs typically use compound interest (quarterly or monthly compounding). Loans use reducing balance EMI calculations which are a form of compound interest working against you. The more frequently your money compounds (daily > monthly > quarterly > annually), the faster it grows.
Albert Einstein may or may not have called compound interest "the eighth wonder of the world," but the math speaks for itself. Understand it viscerally, not just intellectually.
Frequently Asked Questions
What is the key difference between simple and compound interest?
Simple interest is calculated only on the principal amount. Compound interest is calculated on the principal plus all accumulated interest. Over time, compound interest grows exponentially while simple interest grows linearly.
Where is simple interest still used?
Simple interest is common in short-term personal loans, car loans, and some government bonds. Most savings instruments, mutual funds, and FDs use compound interest.
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