Foundation
What is Compound Interest?
The Secret to Exponential Wealth
Compound Interest is the interest calculated on the initial principal AND on the accumulated interest of previous periods. In simple words: you earn "interest on interest", which makes your money grow exponentially over time.
Think of it like a snowball rolling downhill — it starts small, but as it rolls, it picks up more snow, growing larger with increasing momentum. That's exactly how compound interest works with your money.
Compound Interest vs. Simple Interest
Interest calculated only on the principal — never on accumulated interest.
- Linear growth (straight line)
- Same interest every year — forever
- ₹10,000 at 10% = ₹1,000/year always
- Lower long-term returns
Interest calculated on principal + accumulated interest each period.
- Exponential growth (accelerating curve)
- Interest amount increases every year
- ₹10,000 at 10% = ₹1,000 yr1, ₹1,100 yr2…
- Dramatically higher returns over time
Key Insight: Over long periods, compound interest creates exponentially more wealth than simple interest. Einstein allegedly called it "the eighth wonder of the world."
The Compound Interest Formula
Here's the mathematical engine behind exponential growth:
A = P(1 + r/n)^(n×t)
Where:
A = Final amount
P = Principal (initial investment)
r = Annual interest rate (as decimal, e.g. 10% = 0.10)
n = Times interest compounds per year
t = Time in years
──── Example: ₹10,000 at 10% for 3 years ────
A = 10,000 × (1 + 0.10/1)^(1×3)
A = 10,000 × (1.10)³
A = 10,000 × 1.331
A = ₹13,310 (vs ₹13,000 with simple interest)