Index fund or ETF: which one should you buy?

Two wrappers around one index

An index fund and an exchange-traded fund (ETF) can follow the very same index, say the Nifty 50, and hold nearly the same shares in the same weights. What differs is the wrapper: how you buy it, what it costs, and what can go slightly wrong. The index funds and ETFs guide covers the basics; this post is about choosing.

The short version is that both are good, and the better one is the one you will keep buying. Here is how to tell which that is.

How they work in practice

An index fund is bought from the AMC and priced at NAV. An ETF is a listed unit, so its price is set by buyers and sellers during the day. Market makers keep it close to the value of the underlying shares, but a gap can open, especially in thinly traded ETFs or during sharp moves.

The cost question, with arithmetic

ETFs usually carry lower expense ratios, and that is the main reason people choose them. But the expense ratio is not the whole cost. Take an investor putting ₹5,000 a month into an ETF.

Assume the broker charges ₹20 per order (an assumption; your charges may differ). That is ₹20 on ₹5,000, or 0.4% on every purchase, and ₹2,400 over ten years of monthly buying. Add the bid-ask spread, which varies by ETF and moment. If the ETF's expense ratio is lower than the index fund's by, say, 0.1% a year, the saving on a growing balance takes years to make up for a 0.4% charge paid on each instalment.

The reverse holds for a large investor. Someone putting ₹10 lakh in once pays one brokerage charge on a big sum, and a lower expense ratio then wins. So:

• Small, regular amounts: an index fund usually costs less in total.
• Large, occasional purchases: an ETF can cost less.

Check the figures yourself: the expense ratio of Direct index funds is public, and our post on the cheapest Nifty 50 index funds lists the cost side by side. The effect of a small cost gap over decades is shown in the impact of 1% calculator.

Tracking: the number that matters most

Both products aim to match the index, and both fall short by a little. The gap is made of the cost, any cash the fund holds, and the way it trades. Two measures help: tracking difference (how far the fund's return was from the index over a period) and tracking error (how much that gap wobbles). Read index fund tracking error and the guide to tracking error and standard deviation before you trust an index name alone. Two Nifty 50 funds can differ by more than you expect.

Who should pick which

Choose an index fund if:

• you want a SIP that runs without any action from you;
• you do not have a demat account or do not want to manage one;
• your monthly amount is small;
• you would like to sell in part, or switch, without a market price to watch.

Choose an ETF if:

• you already have a demat account and trade regularly;
• you invest larger sums at once;
• you want to buy or sell at a known price during the day;
• you are comfortable checking that the ETF is liquid, with a tight bid-ask spread.

Plenty of people use both: an index fund SIP for the habit and an ETF for occasional lump sums.

Things that apply to both

Tax. Both are treated like equity funds when they are equity-oriented: gains above ₹1.25 lakh a year taxed at 12.5% after a year, 20% before, as of October 2026. Index funds and ETFs that follow international or gold indices are taxed differently, so check the category. The mutual fund taxation guide has the detail.

Direct vs Regular. Index funds come in both plan types. A Regular plan adds a distributor's commission to an already thin margin, which erodes the whole point of choosing an index. See direct vs regular plans. ETFs have no such split.

Which index. Picking a wrapper does not choose the index. The Nifty 50, a Next 50 or a smart-beta index behave differently; our piece on smart-beta index funds looks at the latter. Use the screener or the compare tool to look at several funds on the same index side by side.

Why people choose indexing at all. The case is laid out in why investors are choosing index funds.

A simple decision

1. Do you already hold a demat account and trade? If not, choose an index fund.
2. Is your purchase a small monthly one? Choose an index fund.
3. Is it a large one-time sum, and you are comfortable with a demat account? Compare the ETF's total cost with the fund's.
4. Whichever you pick, choose the one with the lowest tracking difference and a tight cost, and set it up so that you keep buying.

For details of how ETFs trade and are regulated, see SEBI's website and the investor material on AMFI.

This article is for education, not investment advice. Charges, tax rules and fund details change; verify them with the fund house and your broker before you act.