Index Fund vs ETF vs Mutual Fund: The Actual Differences
Two of those words describe a strategy and one describes a wrapper. Here is what actually differs, how a pooled price is computed, and what a fee does.
The comparison as usually written is confused, because the three words are not the same kind of word. Index describes a strategy: follow a published rulebook instead of picking. Mutual fund and ETF describe wrappers: how the thing is priced, traded and settled. An index strategy can sit inside either wrapper, and either wrapper can hold a strategy that is not an index at all. Once you separate strategy from wrapper, the whole subject stops being a three-way fight and becomes two independent questions.
Two questions, not one
| The strategy question | The wrapper question | |
|---|---|---|
| Asks | how are the holdings chosen | how is it priced and traded |
| Options include | follow a published rulebook, or select | mutual fund, or exchange-traded |
| Drives | what is inside, and much of the cost | when you get a price, and how you buy |
| Independent of | the wrapper | the strategy |
Keep those two columns separate and every fund you look at sorts itself into a cell. Merge them, which is what the usual comparison does, and the vocabulary starts contradicting itself.
How a pooled price is computed
For a mutual fund the price is arithmetic rather than negotiation, and it is the same division you would run on a single company, one level up.
| Step | Working | Amount |
|---|---|---|
| Everything it holds | 200 practice companies, priced | $52,000,000.00 |
| What it owes | bills not yet paid, and that day's fee | −$2,000,000.00 |
| Net assets | what the pool is worth tonight | $50,000,000.00 |
| Fund shares outstanding | the denominator, and not the companies' own | 4,000,000 |
| Price per fund share | $50,000,000.00 over 4,000,000 | $12.50 |
Note the denominator carefully. The fund has 4,000,000 of its own shares, which is a completely different floor from any individual company inside it. Never mix the two, and the habit of asking what is on the bottom of this fraction is the same one that makes a single share make sense in what a share actually is.
Forward pricing, and why the cutoff exists
Orders for a mutual fund arrive all day at a price nobody knows yet. That is deliberate and it has a name: forward pricing. It exists to stop anybody trading at a number they already know.
The practical line is a daily cutoff. Land on one side of it and you get tonight's computed figure; land after it and you wait for tomorrow's. An exchange-traded wrapper works differently, trading through the day at whatever the market says, which is the single largest practical difference between the two wrappers and the one that matters least to most long-horizon holders.
The fee leaves from inside, every single day
Nothing is billed and no envelope arrives. The fee accrues daily and the price is simply smaller.
- A 0.60% yearly ratio on $50,000,000.00 of net assets is $300,000.00 a year.
- Which is $821.92 a day.
- Which is $0.000205 per fund share.
- Which adds up to $0.075 a share by year end.
Invisible daily, visible annually, and never itemized anywhere you would notice. That is why the ratio is worth reading before anything else about a fund: it is the one cost you will never see leave.
The worked example: what three-quarters of a percent does
This setup is drawn from a published regulator illustration at investor.gov, and the row-by-row dollars below are our own computation of that setup. $100,000.00 growing at an assumed 4% a year for 20 years, with the year's fee deducted from the grown balance each year. One model for every row. Only the fee moves.
| Yearly fee | Ends at | Fees actually deducted |
|---|---|---|
| 0.25% | $208,413.03 | $7,536.74 |
| 0.50% | $198,211.28 | $14,675.27 |
| 1.00% | $179,213.51 | $27,831.76 |
| The gap | $29,199.52 | 0.75% a year of difference |
Year one's fee at the lowest rate is $260.00, and no envelope arrives for it. At the highest rate, $27,831.76 is deducted across the run, plus the growth those dollars never got to earn. The 4% is an assumption for the demonstration and not a promise about anything, which is exactly why the illustration holds it constant across all three rows: the only variable that is allowed to move is the fee.
What an index actually is
Not weather. A rulebook somebody wrote and somebody maintains, with eligibility tests, a weighting method and a calendar. That document is published. The ruler is a set of choices rather than a fact of nature, and knowing that changes how you read the word.
On a schedule, names that no longer qualify come off and new ones go on. Every fund following that list has to trade to match, at roughly the same time, in the same names. Predictable trading by a crowd is one of several reasons a fund never lands exactly on its list.
Difference and error are two different words
| Line | Working | Result |
|---|---|---|
| A practice starting amount | one year | $10,000.00 |
| The list's year | a practice 6.00% | $10,600.00 |
| The fund's year | 5.98% before its fee | $10,592.00 |
| The gap | $10,600.00 less $10,592.00 | $8.00 |
| After a 0.06% ratio | the fund's own cost | 5.92% |
Tracking difference is how far the fund landed from the list, which is a size. Tracking error is how much that gap wobbles from year to year, which is a steadiness. Five things produce the gap: fees, cash waiting to be invested, holding a sample rather than every name, trading costs, and timing. Some funds also earn income lending securities out, which pushes the other way.
Three parties, three jobs
A fund is a company with staff, a board, a custodian and a deadline every business day. The adviser makes the investment decisions under contract. A separate custodian holds the securities. A board oversees the arrangement for shareholders.
Three jobs, three parties, and one practical consequence worth knowing: an adviser's troubles and a fund's holdings are separate things, because the holdings are not sitting with the adviser.
The comparison that actually matters
- What is the strategy? A published rulebook, or selection. This drives most of the cost.
- What is the ratio? The one cost you will never see leave.
- What is the wrapper? Priced once daily, or traded through the day.
- What is actually held? The holdings are published. The name of the thing is not the thing.
- What does the account it sits in do to the tax? An irs.gov and tax-professional question, not a fund question.
Notice that the wrapper question is third rather than first, which is the opposite of how the comparison is usually framed. It matters, and it usually matters less than the two questions above it.
What the wrapper actually changes for a household
Strip the argument down and the wrapper decides four practical things.
| Question | Priced once daily | Traded through the day |
|---|---|---|
| When do I get a price? | after the close, computed | continuously, negotiated |
| What does trading cost? | no spread on the fund itself | a spread, plus any commission |
| Can I buy a round dollar amount? | usually yes | depends on the platform |
| Does intraday movement matter to me? | no | only if you trade during it |
For somebody buying monthly and holding for years, most of that table is close to irrelevant, which is why the wrapper question deserves third place rather than first. For somebody transacting often, the spread column stops being irrelevant quickly, and what a spread actually costs prices it on a practice quote.
Why time is the other variable
Everything on this page is about cost and structure. The other half of the arithmetic is the run, and the difference a small annual cost makes over twenty years is the same mechanism that makes a small monthly deposit matter over sixty. Compounding, worked year by year runs that from the other direction, on three people at three ages, with the arithmetic shown rather than assumed.
Ratio times balance. That is the number leaving each year without an invoice, and most people have never once computed it.
Going further
How Investing Works computes a practice fund's price to the cent, accrues its fee by the day, and runs the regulator's own fee illustration in code. It names no real fund, index or provider, and it will never tell you what to buy.
investor.gov publishes the original illustration and a great deal else, free, from a federal regulator.
Questions people actually ask
What is the difference between an index fund and an ETF?
They are not opposites, which is why the comparison confuses people. Index describes a strategy: follow a published rulebook rather than pick. ETF and mutual fund describe wrappers, meaning how the thing is priced and traded. An index strategy can sit in either wrapper.
How is a fund's price worked out?
For a mutual fund it is computed, not negotiated. Everything held is priced after the close, everything owed comes off, and the result is divided by the fund's own shares. On the practice fund here, $52,000,000.00 held less $2,000,000.00 owed is $50,000,000.00, over 4,000,000 shares, which is $12.50 each.
How does a fund fee actually get paid?
Nothing is billed. The fee accrues daily and comes out from inside. On the practice fund, a 0.60% yearly ratio on $50,000,000.00 is $300,000.00 a year, which is $821.92 a day, or $0.000205 per share. Invisible daily, $0.075 a share by year end.
How much difference does a fee make over time?
On the published illustration worked here, $100,000.00 growing at an assumed 4% for 20 years ends at $208,413.03 with a 0.25% fee and $179,213.51 with a 1.00% fee. That is a gap of $29,199.52. The growth rate is an assumption for the demonstration, not a promise.
Is this investment advice?
No. This is general financial education about structures. It is not financial advice, not investment advice, and not a recommendation to buy, sell or hold anything. Every fund on this page is invented, no real fund or firm is named, and investor.gov publishes free educational material including the fee illustration this page computes.