What Is Compounding, and Why Does It Matter More Than the Rate?

The one-line version

Compounding is interest (or returns) earning interest on themselves, not just on your original amount. ₹1,00,000 growing at 10% a year becomes ₹1,10,000 after year one - but in year two, that 10% applies to ₹1,10,000, not the original ₹1,00,000. Each year's gain is calculated on a slightly bigger base than the year before.

Why the curve bends upward

In the early years, compounding looks a lot like simple, linear growth - the gap between "growth on your original money" and "growth on your growth" is small. Given enough years, that gap becomes the majority of the final number. Over a 30-year horizon, a large share of the final corpus typically comes from returns earned on previous returns, not from money you actually put in.

A concrete comparison

₹1,00,000 invested once at 10% a year: - After 10 years: roughly ₹2.6 lakh - After 20 years: roughly ₹6.7 lakh - After 30 years: roughly ₹17.4 lakh

The money more than doubled again between year 20 and year 30 - a bigger jump in absolute terms than the entire first 20 years produced, even though the rate never changed. That's compounding, not a change in the rate.

Why "time invested" usually beats "a better rate"

Someone who invests for 30 years at 10% will typically end up with more than someone who invests for 15 years at 14%, purely because compounding needs time to do its work - see our article on why starting a SIP early beats investing more, later, for the fuller version of this argument.

One thing this doesn't cover

How often interest gets added back to your principal (monthly vs. annually) also changes the outcome, even at the same stated rate - a related but separate effect, covered in its own entry.

The takeaway

The rate you earn matters, but the number of years you stay invested usually matters more - compounding rewards patience more reliably than it rewards chasing a marginally higher return.