What it means
An index ETF holds the shares or bonds in an index, in roughly the same proportions as the index itself. When the index changes its membership, the fund adjusts its holdings to match, which is why the manager's job is described as tracking rather than selecting.
The exchange traded part is what separates it from a traditional index fund. Units can be bought and sold during market hours at whatever price the market quotes, while a conventional fund is priced once a day after the close.
Cost is the strongest argument in the ETF's favour. Fees on mainstream index ETFs are often a few hundredths of a percent a year, against roughly 0.5% to 1.5% for actively managed funds, and that gap compounds over decades of holding.
Investors judge an index ETF on tracking difference, meaning how far its return falls short of the index it follows. Fees, cash drag, taxes withheld on dividends and the cost of trading during rebalances all contribute to that shortfall.
The nuance worth knowing is that not all index ETFs are broad or simple. Some follow narrow sector, country or thematic indices that carry concentrated risk, and a few use derivative structures rather than owning the underlying assets at all.
Liquidity is another point of difference that catches people out. What matters is not how heavily the ETF itself trades but how liquid its underlying holdings are, because authorised participants can create and cancel units to meet demand.
In practice
Real-world examples.
Example
A founder selling part of her business puts $400,000 of the proceeds into a broad market index ETF while she decides what to do next, on the grounds that it is diversified, cheap and can be sold on any trading day.
Example
A company pension scheme replaces three underperforming active equity funds with two index ETFs, cutting the equity portion's average fee from 0.72% to 0.09% and saving roughly $189,000 a year on a $30 million allocation. The team also documents the tracking difference of each ETF over three years so that trustees can see how closely the funds have followed their benchmarks.
Example
A finance team managing a corporate reserve wants exposure to short-dated government bonds without running a bond desk, so it buys a bond index ETF and monitors the tracking difference each quarter.
Formula
Calculation
Approximate net return = Index return - Total expense ratio - Other tracking costs, and the value of a holding after one year = Amount invested x (1 + Net return).
Suppose an investor puts $250,000 into an index ETF with a total expense ratio of 0.05%, and the index returns 8% over the year. Net return = 8% - 0.05% = 7.95%. Value after one year = $250,000 x 1.0795 = $269,875, a gain of $19,875.
Compare that with an actively managed fund charging 0.85% that matches the index before fees. Net return = 8% - 0.85% = 7.15%, giving $250,000 x 1.0715 = $267,875. The fee difference alone costs $269,875 - $267,875 = $2,000 in a single year on this holding, and that penalty repeats annually.Case study
Seen in the real world.
Bramley Foods is an invented mid-sized company used for this illustrative case. Its trustees held a legacy equity fund charging 1.1% a year on $18 million, and the fund had trailed its benchmark in six of the last eight years.
The trustees moved $15 million into two index ETFs charging 0.07% and 0.12%. Annual costs fell from about $198,000 to roughly $14,500, a saving close to $183,000 a year before any difference in investment performance.
The fictional trustees were careful to record what they were giving up. They accepted that the funds would never beat the index and would fall just as far in a downturn, and they judged that a near certain fee saving was worth more than an uncertain chance of outperformance.
Watch out
Common mistakes.
- Assuming every ETF is a low-cost index tracker, when many are active, leveraged or thematic products with far higher fees and very different risk.
- Judging an index ETF only on its headline fee and ignoring bid-offer spread, which matters a great deal for anyone trading in and out frequently.
- Believing an index ETF is low risk because it is diversified. It follows the market down as faithfully as it follows the market up.
Questions
People also ask.
What is tracking difference?
It is the gap between the fund's actual return and the index return over a period, and a consistently small gap is the sign of a well-run tracker.
Can an index ETF close down?
Yes, small or unpopular ETFs are wound up regularly, and holders normally receive the cash value of their units rather than losing money outright.
Should an index ETF be bought at market open?
Preferably not, since spreads are usually widest in the first and last minutes of the session, and the middle of the day tends to give a tighter price.
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