Compound Interest — The 8th Wonder of the World Explained
Understand the magic of compound interest with real examples. Learn how compounding frequency, time, and rate affect your wealth.
What is Compound Interest?
Compound interest means earning interest on your interest. Unlike simple interest (calculated only on principal), compound interest grows exponentially over time.
The Formula: A = P × (1 + r/n)^(n×t)
- Where:
- P = Principal amount
- r = Annual interest rate (decimal)
- n = Number of times compounded per year
- t = Time in years
- A = Final amount
The Power of Time — ₹1,000/Month SIP Example
At 12% annual returns:
| Years | Invested | Corpus | Interest Earned |
|---|---|---|---|
| 5 | ₹60,000 | ₹82,486 | ₹22,486 |
| 10 | ₹1,20,000 | ₹2,32,339 | ₹1,12,339 |
| 20 | ₹2,40,000 | ₹9,99,148 | ₹7,59,148 |
| 30 | ₹3,60,000 | ₹35,29,914 | ₹31,69,914 |
Notice how 30 years = ₹35.3L from just ₹1,000/month. The interest earned (₹31.7L) is 8.8x the total investment. That's compounding at work.
Compounding Frequency Matters
₹1 Lakh at 10% for 5 years:
| Frequency | Final Amount | Interest |
|---|---|---|
| Yearly | ₹1,61,051 | ₹61,051 |
| Quarterly | ₹1,63,862 | ₹63,862 |
| Monthly | ₹1,64,531 | ₹64,531 |
| Daily | ₹1,64,866 | ₹64,866 |
Monthly compounding earns ₹3,480 more than yearly compounding on just ₹1L. On ₹1 Crore, that difference becomes ₹3.48 Lakh!
Rule of 72 — Quick Doubling Calculator
Want to know how long it takes to double your money? Divide 72 by the interest rate:
- At 6%: 72 ÷ 6 = 12 years to double
- At 8%: 72 ÷ 8 = 9 years to double
- At 12%: 72 ÷ 12 = 6 years to double
- At 15%: 72 ÷ 15 = 4.8 years to double
This means ₹10 Lakh at 12% becomes ₹20L in 6 years, ₹40L in 12 years, ₹80L in 18 years, and ₹1.6 Cr in 24 years — without adding a single rupee!
Simple vs Compound Interest — The Gap
₹1 Lakh at 10% over different periods:
| Years | Simple Interest | Compound Interest | Difference |
|---|---|---|---|
| 5 | ₹1,50,000 | ₹1,61,051 | ₹11,051 |
| 10 | ₹2,00,000 | ₹2,59,374 | ₹59,374 |
| 20 | ₹3,00,000 | ₹6,72,750 | ₹3,72,750 |
| 30 | ₹4,00,000 | ₹17,44,940 | ₹13,44,940 |
At 30 years, compound interest gives you 4.4x more than simple interest. The longer you stay invested, the bigger the gap.
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