Exchange-Traded Fund
Also known as: ETF
A whole portfolio wrapped into one share that trades all day — the cheapest way to buy a market.
- Asset class
- Fund wrapper (equities, bonds, more)
- Instrument type
- Open-ended fund, listed
- Traded
- Exchange, continuously
- Typical users
- Retail, advisors, institutions
BeginnerWhat is it, really?
An ETF is a basket of investments — often hundreds of stocks — packaged into a single share you can buy and sell on an exchange just like any stock. One S&P 500 ETF share makes you a part-owner of all 500 companies at once.
Two features made ETFs the default building block of modern investing: diversification (one trade spreads your money across an entire market, so no single company can sink you) and cost (index ETFs routinely charge 0.03–0.20% per year, versus ~1–2% for traditional active funds).
Unlike a classic mutual fund, which you can only buy or sell once a day at a price set after the close, an ETF trades continuously at a live market price throughout the session.
IntermediateHow it works in practice
The creation/redemption mechanism
The magic that keeps an ETF's price glued to the value of its holdings is done by authorised participants (APs) — large trading firms that can exchange big blocks of ETF shares ("creation units", often 50,000 shares) for the underlying basket, and vice versa, directly with the fund.
- If the ETF trades above the value of its holdings (its NAV), APs buy the basket, deliver it to the fund, receive new ETF shares, and sell them — pushing the price back down.
- If it trades below NAV, APs do the reverse, redeeming ETF shares for the basket.
This arbitrage keeps the premium/discount to NAV within a few basis points for liquid funds.
What to check before buying
- Total expense ratio (TER) — the annual fee, deducted inside the fund.
- Tracking difference — realised return vs. the index, which includes fees, sampling and securities-lending income.
- Replication — physical (holds the stocks) vs. synthetic (holds a swap with a bank; adds counterparty risk, sometimes better tracking).
- Liquidity — on-screen spread plus the liquidity of the underlying basket.
- Distribution policy — distributing (pays dividends out) vs. accumulating (reinvests them).
AdvancedPricing & valuation
Fair value and the arbitrage bound
Let \(\text{NAV}_t\) be the live ("indicative") value of the basket. Absent frictions, the AP arbitrage enforces
where \(c\) bundles basket trading costs, fund fees and inventory risk. For ETFs on illiquid underlyings (high-yield bonds, EM equities), the ETF price is often the better price-discovery vehicle: the "discount" during stress is the market's live valuation of a stale NAV.
Pricing international ETFs
When the underlying market is closed (e.g. a Japan ETF trading in Europe), market makers price the ETF off correlated live proxies — index futures, FX, ADRs:
Quoted spreads widen with proxy-hedge error — the residual variance of the basket vs. the hedge portfolio.
Synthetic replication
A swap-based ETF holds a substitute basket and receives \( R_{\text{index}} - R_{\text{basket}} \) via a total return swap, collateralised daily; under UCITS rules net counterparty exposure is capped at 10% of NAV. The swap fee is the dealer's price for index access, funding and dividend-tax arbitrage.