Index Fund is a passively-managed mutual fund that replicates the composition of a published market index (Nifty 50, Sensex, Nifty Next 50, etc) so its return tracks the index minus a small expense ratio. No active stock selection; minimum manager discretion.
How it works: The fund holds the same stocks in the same weights as the index. When the index re-balances (semi-annually for Nifty), the fund mirrors the change. Tracking Error (TE) measures how closely the funds return follows the index — good Indian index funds have TE under 0.20% annualised.
Example: A Nifty 50 Index Fund with TER of 0.20%. If Nifty 50 TRI returns 14.0% over a year, this fund delivers approximately 13.8%. Over 20 years, the 0.20% drag compounds to about 4% less terminal wealth versus a hypothetical zero-cost fund — still vastly cheaper than the typical 1.0-1.5% TER of active equity funds.
When to use: Core long-term wealth-building allocation, especially for investors who have neither time nor inclination to vet active managers; SIPs in NPS-equivalent low-cost equity exposure.
When NOT to use: When you have high conviction in an active manager with consistent post-fee alpha (rare). Also avoid micro-AUM index funds (under Rs 100 cr) where tracking error tends to be large.
Caveat: Past performance is not indicative of future returns. Index funds will not protect you from a market crash — they will fall in lockstep with the index.
Related terms: ETF, Tracking Error, Smart Beta.