Compounding is interest earning interest. It sounds modest, but over decades it is the single most powerful force in personal finance, and the reason starting early beats investing more later.
How compounding works
With simple interest, you earn a return only on your original money. With compound interest, you earn a return on your money plus all the returns it has already earned. Each year the base grows, so the growth itself accelerates. The formula is final amount = principal x (1 + rate)^years, and that exponent is what makes the curve bend upward steeply over time.
Why the first decade matters most
Most of compounding's magic happens late, but it depends on time you can only buy early. Consider two investors earning 12% a year. Aisha invests Rs 10,000 a month from age 25 to 35, then stops and never adds another rupee. Bilal starts at 35 and invests Rs 10,000 a month all the way to 60. By 60, Aisha, who invested for just 10 years, often ends up with a corpus close to or larger than Bilal's, who invested for 25 years, purely because her money had more time to compound. Starting early beats investing more.
The Rule of 72
A handy shortcut: divide 72 by your annual return to estimate the years it takes money to double. At 12%, money doubles about every 6 years; at 8%, about every 9 years; at 6%, about every 12. The same rule, applied to inflation, tells you how fast your money loses half its value, which is why beating inflation matters.
See it for yourself
Run a principal through the compound interest calculator and watch the gap between simple and compound growth widen with time. Then try the SIP calculator to see how monthly investing compounds, and turn on inflation to read the real, inflation-adjusted result. The lesson is always the same: time in the market, started early, does the heavy lifting.