An exchange-traded fund, or ETF, is a pooled investment fund you buy and sell on a stock exchange. It holds a basket of assets and aims to mirror the return of an index, sector, commodity or other strategy.
ETF shares trade all day at market prices, while the fund also calculates a net asset value, or NAV, from the value of its holdings. A specialised creation and redemption process helps keep the market price close to the NAV.
What an ETF owns and how it tracks an index
Most ETFs are index trackers. If the target is a broad share index, the ETF will hold many or all of the underlying shares in similar weights. For a bond index, it will hold bonds that match the index rules on maturity, rating and currency. Commodity ETFs might hold the physical metal in storage or use futures to gain exposure. There are also strategy ETFs that tilt towards factors such as value or momentum, and funds that focus on themes like clean energy.
Replication methods vary:
- Full replication buys every security in the index in the right proportion. It’s straightforward, but can be costly for very large or illiquid indices.
- Sampling or optimisation buys a representative slice that aims to behave like the index. It reduces trading costs, at the risk of slightly larger tracking differences.
- Synthetic replication uses derivatives, typically swaps with a bank, to deliver the index return. This can track tightly but introduces counterparty risk, which is usually managed with collateral.
Creation, redemption and why ETFs trade near NAV
ETFs have two markets. In the secondary market, investors trade shares with each other on exchange. Behind the scenes, authorised participants (APs) operate in the primary market. When demand is strong, an AP can deliver the underlying securities to the ETF in exchange for newly created ETF shares, then sell those shares on exchange. When demand is weak, the AP can buy ETF shares and redeem them for the underlying holdings.
This “in kind” creation and redemption allows arbitrage. If the ETF trades above NAV, APs can create shares and sell them, pushing the price down. If it trades below NAV, APs can buy and redeem shares, lifting the price. The mechanism helps to keep the trading price close to the fund’s underlying value, especially in liquid markets.
Two numbers help you judge this in practice:
- NAV per share is the value of the holdings divided by shares outstanding, usually struck once a day.
- Premium/discount shows how far the market price is from NAV. A simple version is (Market Price − NAV) ÷ NAV, quoted as a percentage.
Types of ETF you’ll see on a platform
Choice is wide, but most ETFs fall into a few buckets:
- Broad market funds for large baskets of equities or bonds.
- Sector and regional funds that target industries or geographies, from technology to emerging markets.
- Commodity funds that hold physical metals or use futures. Naming rules vary by region; some trade as ETCs or ETPs rather than formal funds.
- Factor and smart beta that tilt towards value, quality, low volatility or similar rules.
- Hedged share classes that aim to reduce currency swings against the fund’s base currency.
- Distributing vs accumulating. Distributing ETFs pay out dividends or bond coupons in cash. Accumulating versions reinvest income back into the fund.
- Leveraged and inverse that seek a multiple of daily index moves or the opposite direction using swaps and futures. These reset daily and can diverge from expectations over longer holding periods.
Crypto exposure may be packaged as ETFs, ETPs or trusts depending on jurisdiction. Structures, rules and risks differ by market and can change.
Costs, spreads and tracking difference to watch
ETF costs show up in several places:
- Ongoing charges (OCF/TER) are taken within the fund to pay management and operating costs. They reduce the return you see but don’t appear as a separate bill.
- Bid‑ask spread is the gap between the price you can buy and sell at on exchange. Tighter spreads are typical for larger, more liquid funds and for trading during the underlying market’s main hours.
- Brokerage and platform fees vary by provider and venue.
Tracking happens in the real world, so an ETF’s return almost never matches the index perfectly. The difference comes from fees, trading costs, cash drags, sampling and taxes. Two common measures are:
- Tracking difference: fund return minus index return over a period. This shows what investors actually experienced.
- Tracking error: the volatility of that difference. Lower suggests more consistent tracking.
Reading an ETF quote and factsheet
On a broker screen you’ll see a ticker, the last traded price, and level 1 quotes for bid and ask. You may also see the day’s volume, estimated intraday NAV, and an indicative premium or discount. For larger orders, many brokers allow limit and stop orders or access to request-for-quote with a market maker. Exact features vary by provider.
The factsheet and prospectus add crucial details:
- Objective and index: what the fund is trying to track and how the index is built.
- Replication method: physical full, sampling or synthetic.
- Currency and hedging: base currency, trading currency, and whether returns are hedged.
- Income policy: distributing or accumulating, and the schedule for payouts.
- OCF and securities lending: fees and whether the fund lends out its holdings to earn revenue.
- Risk factors: liquidity of the underlying, counterparty risk for derivatives, and concentration limits.
Practical risks and common pitfalls
Liquidity can be layered. A large ETF can still hold illiquid assets. Trading a small-cap equity or niche bond ETF late in the day might mean wider spreads and less depth, even if the fund’s assets under management look healthy.
Premiums and discounts can widen. In fast markets or when the underlying is closed, the ETF price can drift from NAV until APs can trade the basket. Check the estimated intraday NAV and consider using limit orders for control.
Structure risks differ. Synthetic funds and those that lend securities bring counterparty and collateral considerations. Read how collateral is managed and what limits apply.
Compounding effects in leveraged and inverse products. Because these target a multiple of the daily move, holding them for weeks can produce results that diverge from a simple multiple of the index’s cumulative return.
Tax and regulation vary by country and can change. The treatment of fund income, capital gains and withholding taxes differs by jurisdiction and fund domicile. Check current rules that apply to you.
A simple example: buying broad market exposure
Imagine you want low-cost exposure to a large share index. You find an ETF with an OCF of 0.10 per cent, trading at £50.00 with a 1p spread. You place a limit order to buy 100 shares at £50.01. Your order fills. Over the year, the index returns 8.2 per cent. The ETF, after fees and small trading frictions, returns 8.0 per cent. That 0.2 percentage point gap is the tracking difference you observe. If the fund is distributing, you might also receive periodic cash payouts, which you could reinvest or spend depending on your plan.
Behind the scenes, if more investors pile in, an authorised participant delivers the index basket to the ETF and receives new ETF shares to sell. If the ETF starts to trade 0.3 per cent above its NAV, that creation arbitrage encourages selling pressure in the ETF and buying of the underlying, nudging prices back into line.
When investors use ETFs
ETFs fit many roles: a core building block for long-term portfolios, a quick way to adjust regional or sector exposure, a cash-efficient vehicle to hold bonds, or a tool to express a short-term view in a single trade. Traders often like the transparent, on-screen pricing and the ability to set precise order types during market hours. Long-term investors value the diversification, low costs and the choice between receiving or reinvesting income.
The exact mechanics, fees and available markets depend on the exchange, issuer and your platform. Read the fund documentation and your broker’s fee schedule before you trade.