# How Exchange-Traded Funds Work

Understand ETF shares, net asset value, market price, premiums and discounts, creation and redemption, tracking, expenses, liquidity, and concentration risk.

Canonical: https://wiki.fcontext.com/stocks/etf/
Fact checked: 2026-07-13

> For educational purposes only; not investment advice.

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## Direct answer

An **exchange-traded fund (ETF)** is an investment company or product whose shares trade on an exchange. Depending on its mandate, it can hold stocks, bonds, cash, derivatives, commodities, or interests in other assets. Buying one ETF share gives exposure to the fund's portfolio under its legal structure; it is not direct ownership of every underlying asset.

ETF shares have an intraday **market price**, while the fund calculates **net asset value (NAV)** from assets minus liabilities. The two can differ. A fund can provide broad diversification, narrow concentration, leverage, inverse exposure, or another specialized payoff, so the label ETF does not describe its risk by itself.

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## Shares, NAV, and creation/redemption

NAV per share is generally:

`NAV per share = (fair value of assets - liabilities) / ETF shares outstanding`

Retail investors normally buy and sell existing shares on an exchange at bid and ask prices. Certain large institutions, called **authorized participants**, can transact with the fund in large creation units, delivering or receiving baskets of securities and/or cash. Creation and redemption can increase or decrease ETF shares outstanding and help market prices stay linked to portfolio value, but they do not guarantee equality at every moment.

The mechanism depends on reliable prices, tradable underlying assets, functioning market makers, and willing authorized participants. During volatility, foreign-market closures, or stress in bonds and other less liquid assets, NAV estimates and ETF quotes can diverge.

An index ETF seeks to track a specified benchmark before costs; an active ETF follows a manager's mandate. Tracking difference can result from expenses, taxes, cash balances, sampling, trading costs, timing, securities lending, derivatives, and index changes.

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## Price, spread, and expense example

Suppose an ETF's latest NAV is `$50.00` per share and its quote is `$49.90 bid / $50.10 ask`.

- Ask premium to NAV: `($50.10 - $50.00) / $50.00 = 0.20%`
- Bid discount to NAV: `($49.90 - $50.00) / $50.00 = -0.20%`
- Quoted spread: `$50.10 - $49.90 = $0.20`, or `0.40%` of NAV

Buying 100 shares at the ask and immediately selling at the unchanged bid creates a `$20` difference before commissions and fees. Actual NAV may be stale or estimated while underlying markets move, so the calculation is descriptive rather than an arbitrage guarantee.

If the ETF reports a `0.20%` annual expense ratio, `$10,000 × 0.20% = $20` is a rough one-year scale at a constant balance. The fund normally deducts operating expenses from assets over time; investors do not usually receive a separate annual bill, and actual dollar impact changes with value and holding period.

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## Risks to examine

- **Portfolio risk:** ETF shares fall when underlying exposures lose value.
- **Concentration:** a sector, theme, country, or top holdings can dominate results.
- **Tracking difference:** returns can depart from the benchmark.
- **Premium/discount:** market price can move away from NAV, especially under stress.
- **Trading cost:** spread, slippage, commissions, and market impact are separate from the expense ratio.
- **Underlying liquidity:** ETF volume alone does not reveal capacity in the portfolio basket.
- **Structure risk:** derivatives, leverage, daily reset, commodity futures, or notes can create unfamiliar payoffs.
- **Closure and change:** a fund may liquidate, merge, change an index, or alter its strategy subject to its documents and rules.
- **Tax and distributions:** turnover, structure, jurisdiction, and account type affect outcomes.

Read the prospectus, summary prospectus, holdings, index methodology if applicable, fee table, premium/discount history, bid-ask spread, and trading volume. The fund name is not a substitute for examining what it actually holds and how it obtains exposure.

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## Common misconceptions

**"Every ETF is diversified."** A fund can hold one industry, a concentrated theme, derivatives, or a narrow group of securities.

**"ETF price must equal NAV."** Creation/redemption encourages linkage but does not guarantee an exact match.

**"Low expense ratio means low total cost."** Spread, premium, discount, tracking, taxes, and market impact also matter.

**"Low ETF volume means it cannot be liquid."** Underlying-asset liquidity and creation capacity also matter, although displayed spread and depth still affect retail execution.

**"An index ETF guarantees the index return."** Expenses and implementation produce tracking differences, and investors trade at market prices.

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## Related topics

- [Index Funds](/stocks/index-funds/)
- [Diversification](/stocks/diversification/)
- [Bid-Ask Spread](/stocks/bid-ask-spread/)

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## Authoritative sources

- [Exchange-Traded Fund (ETF)](https://www.investor.gov/introduction-investing/investing-basics/glossary/exchange-traded-fund-etf) - SEC Investor.gov (accessed 2026-07-13)
- [Exchange-Traded Funds and Products](https://www.finra.org/investors/investing/investment-products/etfs) - FINRA (accessed 2026-07-13)