How to Choose an Index Fund
To choose an index fund, decide which index you want to own first, then compare every fund tracking it on ongoing charge, tracking difference and fund size. Funds following the same index should deliver nearly identical returns, so cost and tracking are the whole decision.
Choosing between index funds is a narrow, answerable question, because funds tracking the same index are attempting to deliver the same thing. What separates them is cost, how closely they manage it, and a handful of structural details.
Before you start
The index you want to own, decided before any fund is compared. A broad developed-market index and a single-country one are different investments, and no amount of fund comparison bridges that.
Your account type, because domicile and tax treatment follow from it. A sheltered account and a taxable one point toward different share classes.
At least two candidate funds, since every figure here is a comparison. A 0.12% charge is meaningless until something sits next to it.
The steps
1. Choose the index, not the fund
What it holds, how many companies, how it weights them and which countries it includes. This decision determines nearly all of your return; the fund choice determines a fraction of a percent.
2. List every fund tracking that index
There are usually several, from different providers, at different charges. They are attempting the same job, which is what makes a like-for-like comparison possible.
3. Compare the ongoing charge
On this site’s arithmetic a 5-basis-point annual drag removes 1.5% of a thirty-year pot and 75 removes 20.2%. Between two funds tracking one index, that difference is most of the decision.
4. Check the tracking difference, not just the charge
The gap between the fund’s return and the index’s is the true cost of ownership. A cheaper fund that tracks poorly can end up behind a dearer one that tracks well.
5. Look at replication method
Physical replication holds the underlying securities. Synthetic uses a swap agreement with a counterparty, which can track more precisely and introduces a counterparty you did not choose.
6. Choose accumulating or distributing deliberately
Accumulating reinvests income inside the fund. Distributing pays it out. Which suits you depends on whether you want the income and on how each is treated in your account.
7. Check fund size and provider before committing
A very small fund can be merged or wound up, which sells your holding on a date somebody else chose. In a taxable account that is a realised gain you did not plan.
How to tell it worked
The index was chosen before any fund, and you can say what it holds.
At least 2 funds tracking it were compared on the same 4 fields.
Tracking difference was checked, not just the headline charge.
And the replication method and income treatment were both decided rather than inherited, which is about 10 minutes of reading.
What does not differentiate them
Past performance. Two funds tracking one index have nearly identical returns by construction, and any difference between them is mostly the two things above.
Brand and marketing. The provider matters for continuity and scale, not for the returns, and a larger provider is a stability argument rather than a performance one.
Where the real differences hide
Domicile affects the tax on dividends inside the fund, before anything reaches you. Two otherwise identical funds domiciled differently can deliver measurably different net returns on the same index.
Securities lending is common and rarely prominent. The fund lends holdings out for a fee, which can improve tracking and introduces a small counterparty exposure. Whether the income is returned to the fund or shared with the manager varies.
Currency hedging is a separate product. A hedged share class removes the currency exposure and costs more; whether you want it is a decision about what you are trying to own.
Fund or exchange-traded version
Many indices are available in both wrappers, and the choice is mostly about how you buy rather than what you own.
A fund prices once a day and takes orders in currency amounts. That suits regular contributions, because a fixed monthly amount buys whatever fraction it buys with no leftover cash.
An exchange-traded version trades through the day at a live price and pays a spread. That suits larger, less frequent purchases, and the spread is a per-transaction cost the daily-priced fund does not charge.
For a monthly contribution the fund version is usually simpler and cheaper in practice, because twelve small spreads a year add up to more than the difference in charge between the two wrappers.
The original data
Of the 24,971 unique videos in research/search-study-corpus.jsonl, 132 mention index funds in the
title, at a median of 69,951 views across 87 channels, and 44% of those titles are instruction-shaped.
Mutual funds appear in 38 at 170,093 and exchange-traded funds in 449 at 12,651. The counts come from
site/rank_investing.py, which deduplicates by video id.
132 videos at 69,951, one of the largest audiences per video in the whole investing ranking. Almost all of it argues for index funds as a category, and very little of it addresses choosing between the several that track the same index.
The answer to the question on that chart is that 3 basis points is worth well under 1% of a thirty-year pot. In a taxable account, selling to capture it realises gains that will exceed it many times over. Cost differences matter at the point of choosing, and much less once you already hold something.
When it fails
The failure is choosing the fund and never examining the index, and it produces a portfolio nobody designed. Two funds are compared carefully on charge and tracking, the cheaper one wins, and nobody asks what it holds. It turns out to be a single-country index, or one weighted heavily toward a handful of very large companies. The fund is doing its job perfectly — the exposure is simply not the one that was wanted, and the careful comparison was applied to the smaller half of the decision.
The second failure is comparing on charge alone. Tracking difference is the real cost.
A third is ignoring replication method. Synthetic adds a counterparty.
A fourth is inheriting the income treatment. Accumulating and distributing suit different accounts.
A fifth is buying a very small fund. Closure forces a sale on somebody else’s schedule.
And a sixth is switching for a few basis points. In a taxable account the transaction outweighs it.
Related
Index funds covers what they are and why tracking is the proposition. Expense ratio is the annual charge and what it does over decades. And tracking error is the gap between the fund and the index it follows.
The realisation that simplified this was that two funds tracking the same index are the same product. Once I accepted that, the comparison stopped being about which one is better and became about which one costs less to hold and follows the index more closely — two questions with findable answers.
— Michael Whitman
This page is educational, not financial advice. Test every idea on your own charts before risking money.