Compound interest, explained with rice grains
Feel — not just calculate — what time does to money.
Simple vs compound
Simple interest pays only on what you put in. Compound interest pays on your money and on the interest it has already earned. ₹10,000 at 7% simple is ₹17,000 after ten years. Compounded, it is ₹19,672 — and after twenty-five years the gap is larger than the original deposit.
The rice-grain doubling
One grain on the first square of a chessboard, doubling each square. By square 21 the room is out of rice. Nothing changed except time. Money behaves the same way — which is why a woman who starts at 25 with ₹500 a month finishes ahead of one who starts at 40 with ₹2,000.
The rule of 72
Divide 72 by the interest rate to find how many years money takes to double. At 6%, twelve years. At 12%, six. Use the same rule on debt: a loan at 36% doubles what you owe in two years.
Two participants: one saves ₹500/month for 10 years then stops; the other starts 10 years later and saves ₹1,000/month for 20 years. The group computes both. The early saver usually wins on less money.
Time does more work than amount. Start small, start now.