What Is an ETF? Exchange-Traded Funds Explained

Exchange-Traded Funds (ETFs) have revolutionized investing by making diversification simple and affordable. This guide explains everything you need to know.

How an ETF works, mechanically

An ETF holds a pool of underlying securities and issues shares representing fractional ownership of that pool. Those shares trade on an exchange, so you buy and sell them through a broker at market prices during trading hours, rather than at a single end-of-day price. The fund's market price stays very close to the value of its underlying holdings because of an arbitrage mechanism involving large institutional 'authorised participants' who can create or redeem shares in bulk.

That mechanism matters to you for one practical reason: it keeps ETFs from trading at meaningful premiums or discounts to their net asset value (NAV). For large, liquid ETFs the gap is usually a fraction of a percent. For small, thinly traded ETFs it can widen, which is a real cost.

ETFs also differ from mutual funds in how they handle taxes. Because of the creation/redemption process, ETFs rarely need to sell holdings to meet redemptions, so they distribute far fewer capital gains — often none. In a taxable account that is a meaningful annual advantage.

What to check before buying one

Four numbers decide whether an ETF is a good vehicle: expense ratio (lower is better; index ETFs are usually 0.03-0.20%), assets under management (under roughly $50 million signals closure risk), average daily volume or bid-ask spread (a wide spread is a hidden cost on every trade), and tracking difference — how closely the fund has followed its index after fees.

Also read the name carefully. 'Leveraged' and 'inverse' ETFs rebalance daily and are designed for short-term trading, not long-term holding; their returns over months can diverge wildly from what the name suggests. 'Thematic' ETFs concentrate in a narrow sector and offer far less diversification than a broad index fund at a higher fee.

Worked example: $20,000 over 20 years, 0.05% vs 0.75%

You invest $20,000 in a broad market ETF with a 0.05% expense ratio, growing at an average 7% gross return. Net return is 6.95%. After 20 years the balance is about $76,700.

The same $20,000 in a fund charging 0.75% nets 6.25% — after 20 years about $67,300. The difference is $9,400, or 12% of the final balance, lost purely to a higher fee for the same market exposure.

Now add the tax angle. In a taxable account, a mutual fund that distributes capital gains annually forces you to pay tax on gains you did not choose to realise. An equivalent ETF often distributes nothing. At a 15% capital gains rate on even a modest annual distribution, that difference compounds into another few thousand dollars over 20 years.

ETF vs mutual fund

Risks and Points of Caution

• Leveraged and inverse ETFs reset daily and are unsuitable for long-term holding despite their names.
• Thinly traded ETFs can have wide bid-ask spreads, which is a real cost on every trade.
• Small funds (under roughly $50 million) may close and force you to sell, potentially creating a taxable event.
• Sector and thematic ETFs concentrate risk and charge higher fees than broad index funds.
• An ETF's market price can briefly deviate from its net asset value in volatile conditions.

What to do next

Four checks before any purchase.

1. Check the expense ratio — under 0.20% for a broad index ETF.
2. Confirm assets under management are above $50 million to avoid closure risk.
3. Look at the bid-ask spread; trade during market hours and avoid market orders on thin funds.
4. Read the fund name: avoid 'leveraged', 'inverse', and narrow 'thematic' products for long-term holding.
5. Compare the tracking difference against the index over three and five years.
6. Use limit orders rather than market orders for less liquid ETFs.