Index Fund or ETF: Does It Matter?

The same index, held two ways, in a taxable account, on $100,000 for five years: the ETF ends $312.46 ahead. That is about $62 a year on a six-figure balance, and it is the entire difference people argue about.

The answer for most readers is that it does not matter, and we would rather say so in the first paragraph than build a page that implies a decision exists in order to have something to write about. There are three cases where the choice is real, and they are the last three quarters of this article.

What is actually different?

Nothing about what you own. An index fund and an ETF tracking the same index hold the same companies in the same proportions, because both are following the same published rule. The SEC describes both as pooled vehicles in its glossary entries for mutual funds and exchange-traded funds, and the substantive differences are all in the plumbing.

Two rows in that table do real work. The tax row, and the fractional row. Everything else is either the same for both or matters only to people trading during the day, which is not what either product is for.

The tax difference, on a real balance

Here is the mechanism, because the reason matters more than the conclusion.

When investors sell out of a mutual fund, the fund sometimes has to sell holdings to raise the cash. Selling holdings realises capital gains, and those gains are distributed to everyone still in the fund. You receive a taxable distribution because somebody else left. An ETF can usually meet redemptions by handing securities to large institutions rather than selling them, which does not realise a gain.

That is a genuine structural advantage, and here is its size. $100,000 in a taxable account, 7% a year, 1.5% of it as dividends, long-term gains and qualified dividends both taxed at 15%, and the mutual fund distributing 0.3% of its value each year as capital gains while the ETF distributes nothing.

The realistic comparison is the first two rows: $312.46 over five years, which is 0.225% of the balance. Real, worth having, and not the landslide the wrapper debate implies.

Note the third row, though. A fund distributing 1% a year ends $1,039.35 behind the ETF over the same period, and actively managed funds can distribute far more than that in a year they reposition. The tax-efficiency argument is strong against active funds and weak against index funds, and the two get conflated constantly.

Compare that with the fee difference

Here is the check almost nobody runs, and it is the reason to stop optimising the wrapper.

The same $100,000 over the same five years, varying only the expense ratio:

Three hundredths of a percentage point, from 0.03% to 0.06%, is worth $196.28 over five years. The tax advantage you were weighing is $312.46. They are the same order of magnitude, which means a decision made on the wrapper while ignoring the fee is a decision made on half the evidence.

And both are small beside the fee question that actually matters. The gap between 0.04% and 0.85% over thirty years is $70,624, which is the arithmetic in what 0.85% actually costs you. Choosing the cheap wrapper and then holding it in a plan charging 1.30% is straining at a gnat.

The three cases where it genuinely matters

1. A large taxable balance you will hold for decades. At $500,000 the 0.225% becomes around $1,560 over five years, and it compounds. If you are investing outside retirement accounts at that scale, take the ETF, and take it in a fund with a low turnover.

2. Your broker will not let you invest automatically in one of them. This decides it more often than tax does. If the mutual fund supports a standing monthly purchase and the ETF does not, take the mutual fund, because an automated $400 that happens every month beats a manual $400 that happens nine times a year. That is the whole argument in automating savings so willpower is not involved, and it is worth more than 0.225%.

3. You are in a 401(k). Then the question is usually settled for you, because most plan menus contain mutual funds and no ETFs. It is also the account where the tax difference is exactly zero, since nothing is taxed until withdrawal. Spend the time on the expense ratio instead.

So which one

In a 401(k) or an IRA: whichever is cheaper. The wrapper is irrelevant.

In a taxable account: the ETF, slightly. Take it if the fees are equal and your broker supports fractional shares and automatic investing. If either of those is missing, take the mutual fund and accept the $62 a year.

What we would not do is sell an existing index fund in a taxable account to buy the equivalent ETF. Selling realises the gains you were trying to defer, and a 15% rate on a $40,000 gain is $6,000 today to save $62 a year. That trade takes 97 years to break even. Hold what you have and direct new money to the ETF if you prefer it.

When this does not apply

If the two funds do not track the same index. This entire comparison assumes identical holdings. An S&P 500 ETF and a total-market index fund are different investments, and the difference between them is worth far more than the wrapper. Check what the fund actually holds, which is the first section of index funds explained.

If you are tempted to trade. An ETF prices continuously, and a price that moves in front of you invites action. If you know you will check it, the once-a-day pricing of a mutual fund is a feature rather than a limitation, and it is worth more than 0.225% to someone who would otherwise sell in a bad week.

If you are investing small amounts and your broker has no fractional shares. A $400 monthly contribution into a $290 ETF share buys one share and leaves $110 in cash. Do that for a year and $1,320 never got invested. Use the mutual fund.

If you hold the fund in a taxable account and expect to give it away or leave it. Charitable gifts of appreciated shares and inherited assets are treated differently from a sale, and in both cases the deferred gains may never be taxed at your rate. That changes the calculation enough to be worth its own conversation with someone licensed to have it.

Next steps

1. Check which account you are asking about. If it is a 401(k) or an IRA, stop here and go and look at the expense ratio instead.
2. For a taxable account, look up the capital gains distribution history of the mutual fund you are considering. Index funds usually show years of zeros, and that tells you the tax argument does not apply to that fund.
3. Compare the expense ratios of both wrappers. The gap is often the same size as the tax difference and points the other way.
4. Check whether your broker supports fractional shares and automatic investing for the ETF. If not, take the mutual fund.
5. Do not sell an existing holding to switch wrappers in a taxable account.