How interest earning interest creates exponential growth over time, rewarding early savings and punishing long-term debt.
What is compound interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. In everyday terms, it is "interest on interest."
How does compounding work?
In simple interest, your earnings stay constant every year. In compound interest, each year's interest is added back to the principal, so the base on which future interest is calculated grows larger each cycle.
If you invest ₹10,000 at 10% annual compound interest:
- Year 1 — 10% on ₹10,000 = ₹1,000. New balance: ₹11,000.
- Year 2 — 10% on ₹11,000 = ₹1,100. New balance: ₹12,100.
- Year 3 — 10% on ₹12,100 = ₹1,210. New balance: ₹13,310.
The standard formula for the final amount is:
A = P (1 + r / n)^(n t)
where P is principal, r is the annual interest rate, n is the number of times interest compounds per year, and t is time in years.
The snowball of time
Over short periods, compounding looks almost identical to simple interest. But because the growth rate multiplies itself, compounding produces an exponential curve that bends steeply upward over decades.
Eventually, the interest generated each year dwarfs the original principal. This makes time the single most critical factor in investing: starting early with modest amounts produces far more wealth than starting late with large sums.
The double-edged sword
Compound interest works with equal force in both directions. When you save and invest, it accelerates your wealth. But when you carry revolving high-interest debt, compounding multiplies what you owe, turning small unpaid balances into overwhelming liabilities.
Ai disclosure: written with the help of AI (ChatGPT). You are encouraged to point out errors and omissions.
