How ETFs actually work

An ETF pools many holdings inside one fund and divides the fund into shares. The basket might follow a stock index, hold bonds, track a commodity or follow an active manager's decisions. ETF describes the wrapper and trading mechanism, not the contents.

Investors trade ETF shares with one another on an exchange while the market is open. That is the share-like part. Underneath, the fund still owns the basket and calculates the value of those holdings. The ETF against mutual fund comparison separates this trading mechanism from a mutual fund's once-per-day dealing.

Indexing is another separate choice. An ETF can follow an index or be actively managed, and an index fund can use either an ETF or mutual fund wrapper. What a stock index is explains the selection and weighting rule that an index-tracking ETF copies.

Two prices matter. Net asset value, usually shortened to NAV, is the fund's assets minus its liabilities, divided by ETF shares outstanding. The market price is what buyers and sellers agree for an ETF share on the exchange. They are produced by different processes, so they can differ.

The link between them is creation and redemption. An authorised participant can deliver the fund's prescribed basket of securities and receive a block of newly created ETF shares. It can also return a block of ETF shares and receive the basket. The institution can then trade whichever side is priced more richly.

If ETF shares trade above the basket's value, creating shares and selling them adds ETF supply while buying the basket adds demand for its holdings. If ETF shares trade below the basket, buying ETF shares and redeeming them removes ETF supply while the received basket can be sold. Competition around those exchanges tends to pull the two values together.

This mechanism does not promise an identical price at every instant. When the underlying market is closed, thin or moving quickly, the ETF price can be the freshest estimate available while the displayed NAV is based on older marks. The relevant comparison is still price against the value of the basket at the same moment.

The fund's expense ratio is only one cost. Buying and selling ETF shares also crosses the bid-ask spread, the gap between the highest current bid and the lowest current offer. A narrow spread can matter more than a tiny fee difference to someone who trades often, while the annual fee has more time to matter to someone who holds for years.

A market order accepts the best available price, which can move while the order is being filled. A limit order sets the worst price the investor will accept, but it may not trade. Those are execution choices around the wrapper, not properties of the underlying basket.

The creation process also helps a fund absorb large flows without buying or selling every holding for cash. In-kind exchanges can reduce trading inside the portfolio and can make the ETF wrapper tax efficient under United States rules. Tax treatment depends on the account, the fund and the holder's jurisdiction, so it sits outside the return arithmetic here.

An ETF's annual fee accrues inside the fund. The net asset value is lower than it would have been without that charge, so no separate invoice arrives. If the holdings return $g$ and the annual charge is $f$, a useful yearly approximation is a net return of $g-f$.

For an opening balance left alone, the teaching calculation is

$$A = P(1+r)^n$$

where $P$ is the starting amount, $r$ is the return reaching the holder and $n$ is the number of yearly periods. With $10,000, 7 percent and 20 years, the ending value is $38,696.84, including $28,696.84 of growth. At 6.30 percent, representing the same 7 percent before a 0.70 percent fee, the ending value is $33,936.36, including $23,936.36 of growth.

The 0.70 percent fee line therefore finishes at $33,936.36 against $38,696.84. The fee removed from each year's balance also stops earning later returns. Investment fees and drag develops that compounding effect, and the expense ratio impact calculator lets the return, fee and holding period change.

The exchange listing makes an ETF easy to trade. It does not make the holdings broad, liquid or low risk. A fund concentrated in one industry remains concentrated, and a bond ETF still responds to interest rates and credit conditions. The label says how interests in the basket trade, not what risks the basket contains.

The useful reading order is the index or mandate, the holdings, the expense ratio, the spread, and then any tax features relevant to the account. Two ETFs with similar names can follow different selection rules and hold noticeably different portfolios.

The return examples on this page use a fixed annual rate solely to show fee drag. Real returns change from period to period, and an ETF can lose value. This is educational material, not financial advice.