1.1.6 Compounding

Earnings that earn earnings

Simple interest pays you a return on your original amount, year after year, and nothing more. Compounding pays you a return on the original amount and on every rupee of return you've already earned. The gap between the two starts small and widens every single year, because the base that's earning a return keeps growing.

This is why the same rate of return produces wildly different outcomes depending on how long money stays invested. Compounding does most of its work late, not early, which is exactly why the years often written off as "not much happening yet" matter the most.

The formula behind this is future value = principal times (1 + rate) raised to the power of the number of years. The exponent is what does the work. Doubling the return rate roughly doubles the annual growth, but doubling the time period has a far larger effect because the growth is exponential, not linear. This is the mathematical reason a smaller amount invested early can end up worth more than a larger amount invested later.

What it looks like over time

₹1 lakh growing at 12% a year is worth roughly ₹1.75 lakh after five years, ₹3.1 lakh after ten, and close to ₹9.6 lakh after twenty. The growth in the first five years and the growth in the last five years look nothing alike, even though the rate never changed.

Look at where the growth actually happens. In the first five years the money grew by about ₹0.75 lakh. In years sixteen through twenty it grew by roughly ₹4.5 lakh, six times as much, at the identical 12% rate. The difference is entirely the size of the base: 12% of ₹8 lakh is far more than 12% of ₹1 lakh. This is the steep part of the curve, and it only arrives for money that has been left invested long enough to reach it.

The one variable you control most

You cannot control the market's return in any given year. You can control how long money stays invested and how early it starts compounding. Time is the input with the most leverage in the entire equation, which is why starting early consistently beats trying to catch up later with larger contributions.

This is also why interruptions are costly. Withdrawing and reinvesting, switching funds based on recent performance, or moving to a lower-returning instrument all reset the compounding chain and often trigger a tax event that shrinks the base. Equity held for the long term defers tax until redemption, letting the full pre-tax amount keep compounding, which is one underappreciated reason long-held equity funds compound more effectively than instruments taxed every year.