What Is an Index Fund? How It Works + How to Invest in India
Index funds mirror the Nifty 50 or Sensex automatically, no active manager, fees as low as 0.10%, and have 12%+ long-term returns. Here's how they work and how to start investing.
An index fund is like a mutual fund that mirrors a stock market index, like the Nifty 50 or Sensex, by holding the same stocks in the same proportions. No fund manager, no active stock-picking. In India, Nifty 50 direct plans charge just 0.10–0.15% per year in fees. The Nifty 50 has delivered roughly 12.4% CAGR over 20 years, and SPIVA India data shows more than 70% of large-cap active funds underperform the index over a 10-year period.
By early 2026, passive funds held over ₹11 lakh crore in India. That’s not a niche anymore. But plenty of retail investors still can’t clearly explain what an index fund actually does, which is worth fixing before putting money into one.
What is an index fund?
An index fund is like a mutual fund that mirrors a stock market index by holding the same stocks in the same proportions. That’s the whole idea.
If Reliance Industries is 9% of the Nifty 50, a fund tracking it holds 9% in Reliance. HDFC Bank at 12%? The fund holds 12% in HDFC Bank. When the index moves, the fund moves with it, up or down.
No fund manager is making calls here. No one is deciding what to buy or sell. The fund’s job is to copy the index, nothing more.
How does an index fund work?
A fund house like UTI, HDFC AMC, Nippon India, ICICI Prudential, etc., creates a fund tied to a specific index. The fund holds stocks in the same ratio as the index’s current composition. When NSE rebalances the Nifty 50 (a stock exits, a new one enters), the fund adjusts automatically. Investors buy and sell units at the NAV, which is calculated at the end of each trading day.
Because there’s no research team, no active stock-picking, and no fund manager to pay, the annual cost is very low: typically 0.10%–0.20% per year for Nifty 50 direct plans, versus 1%–2% for actively managed equity funds.
The gap matters more than it looks. On ₹10 lakh invested over 20 years at 12% CAGR, a 1.5% annual cost difference translates to roughly ₹40–50 lakh less in final corpus.
Types of index funds in India
India has funds tracking a wide range of indices. The main ones:
| Index | What it tracks | Example funds |
|---|---|---|
| Nifty 50 | Top 50 companies by market cap on NSE | HDFC Index Fund – Nifty 50, UTI Nifty 50 |
| BSE Sensex | Top 30 companies on BSE | Nippon India Index – Sensex, HDFC Index – Sensex |
| Nifty Next 50 | Companies ranked 51–100 by market cap | ICICI Prudential Nifty Next 50, UTI Nifty Next 50 |
| Nifty Midcap 150 | Mid-sized Indian companies | Motilal Oswal Nifty Midcap 150 |
| Nifty Bank | Top banking and NBFC stocks | UTI Nifty Bank Index Fund, Kotak Banking ETF |
| Nifty IT | Top IT sector companies | Mirae Asset Nifty IT ETF, HDFC Nifty IT ETF |
| S&P 500 (International) | Top US companies | Mirae Asset S&P 500 Top 50 ETF FoF |
For most investors starting out, Nifty 50 or Sensex is the obvious choice, these cover India’s largest, most liquid companies, with decades of track record behind them.
Index fund vs active mutual fund
| Index fund | Active mutual fund | |
|---|---|---|
| Management | Passive — follows the index | Fund manager picks stocks |
| Expense ratio | 0.10%–0.20% | 1.0%–2.0% |
| Returns | Match the market | Higher or lower than the market |
| Consistency | You always get the index | Varies by manager and conditions |
| Underperformance risk | Low | Higher |
| Tax efficiency | Higher (less portfolio churn) | Lower |
The SPIVA India data is fairly uncomfortable for active managers: over a 10-year period, more than 70% of large-cap active funds underperform the Nifty 50. The longer you look, the worse it gets.
Active funds aren’t useless — strong mid-cap and small-cap managers have delivered real returns. But for large-cap exposure, the cost advantage of index funds is difficult to overcome consistently.
What returns can you expect from an index fund?
The Nifty 50 over different time periods:
| Period | Approximate CAGR |
|---|---|
| 1 year (2024) | 8.8% |
| 3 years | 11.2% |
| 5 years | 15.8% |
| 10 years | 13.1% |
| 20 years | 12.4% |
A Nifty 50 index fund on a direct plan will deliver roughly these numbers, minus 0.10–0.20% in fees — so around 12.2–12.3% over a 20-year horizon.
It's worth saying plainly: these numbers include the 2008 crash (Nifty down about 60%), the 2020 COVID crash (down 38% in 45 days), and multiple corrections of 15–25% along the way. The CAGR only holds for investors who stayed through all of it. That’s a harder requirement than the number makes it sound.
How to invest in index funds in India
- Open a demat and trading account — needed for buying ETFs on NSE or BSE. Not required for regular mutual fund units via platforms like Zerodha Coin or Groww.
- Choose an index — Nifty 50 for most investors. Nifty Next 50 or Midcap 150 for more growth potential with more volatility. S&P 500 FoFs for US exposure.
- Pick a specific fund — compare expense ratio, tracking error, and AUM (see below).
- Choose the direct plan — direct plans skip distributor commissions, so you keep 0.3–0.5% more each year. That adds up over 15 years.
- Start a SIP — invest a fixed monthly amount. ₹500/month over 20 years at 12% returns compounds to a real number.
- Leave it alone — index funds don’t work for 1–3 year goals. Volatility takes time to smooth out.
How to choose the best index fund in India
Four things matter here, in order of importance:
Expense ratio. For Nifty 50 direct plans, anything above 0.20% is high. UTI Nifty 50 Direct and HDFC Index Fund Nifty 50 Direct charges are 0.10%–0.15%.
Tracking error. This measures how accurately the fund copies its index. Below 0.10% is good. Consistently above 0.20% is a problem — the fund is drifting from its benchmark.
AUM. Larger is better for liquidity and impact cost. For Nifty 50 funds, prefer at least ₹5,000 crore in AUM. Very small funds can drift from the index due to cash drag.
Fund house. Stick to SEBI-registered AMCs with a proper track record: HDFC AMC, UTI, Nippon India, ICICI Prudential, SBI Mutual Fund.
What index funds do well — and what they don’t
They work well when:
- You want low-cost, broad equity exposure
- You’re investing for 10+ years
- You don’t want to spend time picking funds or managers
- You want to know exactly what’s inside your portfolio
They don’t work well when:
- You want to beat the market
- You need protection during downturns — the fund falls when the index falls
- You’re investing for a goal in the next 2–3 years
- You want sector-specific bets
Disclaimer: This article is for educational purposes only and does not constitute investment advice. Mutual fund investments are subject to market risks. Please read all scheme-related documents carefully before investing.