Compounding happens when the returns an investment earns are reinvested and start earning returns of their own. In the first year you earn on your principal. In the second, you earn on the principal plus the first year’s gains. Over time, the gains on gains can grow larger than the gains on the original amount.
Why it matters
Compounding is why time matters so much. The same monthly investment started ten years earlier can build a dramatically larger corpus — not because more money went in, but because early contributions had longer to compound. It works in reverse too: costs, inflation and debt also compound.
How to read it
- Rate and time multiply. More years often matter more than a slightly higher rate.
- The rule of 72 is a quick check: divide 72 by the annual rate to estimate the years needed to double. At 8%, about 9 years; at 12%, about 6.
- Interruptions are costly. Withdrawing gains or stopping contributions early cuts off the steepest part of the curve.
Common misconceptions
- “Compounding means steady growth.” Compounding amplifies whatever returns you actually get. In market-linked investments, returns vary and can be negative; smooth calculator curves are illustrations.
- “It only works with large amounts.” It works on any amount. Time is the scarcer ingredient.
Note: The Cost of Waiting tool shows how a delayed start changes the monthly amount a goal may need, using assumptions you control.
Formula
Future value = Principal × (1 + r ÷ k)^(k × t), where r is the annual rate, k the number of compounding periods a year and t the number of years
Worked example
For illustration, assume ₹1,00,000 invested at a hypothetical 10% a year, compounded annually. After 10 years it is about ₹2,59,000; after 20 years, about ₹6,73,000; after 30 years, about ₹17,45,000. The last ten years add more than the first twenty combined.
Figures are for illustration only — not a forecast or a recommendation.
Related terms
Inflation
The rate at which prices rise over time, which steadily reduces what a fixed amount of money can buy.
Real return
Your return after accounting for inflation — the growth in what your money can actually buy.
SIP
Systematic Investment Plan
A way to invest a fixed amount in a mutual fund at regular intervals, usually monthly, instead of investing everything at once.
CAGR
Compound Annual Growth Rate
The steady yearly growth rate that would take an investment from its starting value to its ending value over a given period.
Lumpsum
Investing a single, larger amount at one time, rather than spreading it across instalments.
Rupee cost averaging
Investing a fixed amount at regular intervals, so you buy more units when prices are low and fewer when they are high.