Reading an ETF: Expense Ratios, AUM, Liquidity, and the Fact Sheet

Two ETFs can track the same index and look interchangeable on a broker's search screen, yet one quietly costs you more, trades at a worse price, or shadows the index less faithfully. The difference is buried in the fact sheet and the key information document, a one- or two-page summary that most beginners skim and most professionals read line by line. This article teaches you to read it like an analyst, so you can tell a well-built fund from a merely well-marketed one.

The basics

Every regulated ETF comes with two short documents. The fact sheet is the issuer's marketing-and-data summary: objective, holdings, performance, costs. In the UK and Europe, the KID (Key Information Document, the successor to the KIID under PRIIPs rules) is a standardised regulatory sheet covering risk, costs, and scenarios. Together they contain almost everything you need.

The figures that matter most:

• Ongoing charge (OCF) / total expense ratio (TER). The annual percentage the fund deducts from your returns. The single most reliable predictor of long-term net performance. Lower is better, all else equal.
• Assets under management (AUM). How much money the fund holds. Larger funds are usually cheaper to run, less likely to close, and often more liquid.
• Bid-ask spread. The gap between the buy and sell price on the exchange, an implicit cost paid every time you trade.
• Tracking difference. How far the fund's actual return has trailed its index, the real-world measure of how well it does its job.
• Replication method. Physical (full or sampled) or synthetic, which tells you what you actually own.
• Index tracked. The benchmark itself, which determines your exposure.
• Domicile and share class. Where the fund is based (Ireland, Luxembourg, the US) and whether the class is accumulating or distributing, both with tax consequences covered later.

A useful habit: the headline OCF is the cost the issuer wants you to see; the total cost of ownership is OCF plus spread plus any transaction or platform fees. For a long-term holder the OCF dominates; for an active trader the spread can dominate.

Going deeper

Cost is more than the OCF. UK and EU KIDs now break costs into entry/exit, ongoing, and transaction costs, plus any performance fee. Transaction costs, the fund's own internal trading, are real but often overlooked because they sit outside the headline OCF. For a broad-market tracker they are usually tiny; for a high-turnover thematic or active ETF they can be material. Read the cost table, not just the front-page number.

AUM and fund viability. Size is not everything, but very small funds carry a quiet risk: closure. A sub-scale ETF that never attracts assets may be wound down, forcing you to sell at an inconvenient time and possibly crystallising a taxable gain outside a shelter. As a rough guide, a fund comfortably above the tens-of-millions mark, with a clear sponsor and steady inflows, is unlikely to close. Newly launched funds deserve extra scrutiny here.

Liquidity has two layers. On-screen liquidity is the volume and spread you see on the exchange. Underlying liquidity is how easily the fund's holdings can be traded, which (via the creation/redemption mechanism) is what really determines whether a large order can be filled near fair value. A low-volume ETF holding blue chips can absorb a big trade; a high-volume ETF holding illiquid assets may not. Judge liquidity by the holdings, not just the volume figure.

Tracking difference over time. A single year tells you little. Look at the fund's return versus its index over three to five years. A well-run physical tracker trails its index by roughly its OCF; a fund trailing by noticeably more is leaking returns somewhere, poor execution, cash drag, or unfavourable withholding tax. Some funds even slightly beat their index before fees through securities lending income, which carries its own small risks.

The risk indicator and scenarios. The KID's summary risk indicator (a 1-to-7 scale) and its performance scenarios are standardised and useful for comparison, but treat the scenarios as illustrative arithmetic, not forecasts. They are modelled, not promised.

A quick worked comparison. Imagine two S&P 500 trackers. Fund A: OCF 0.07%, AUM £8bn, penny spread, five-year tracking difference of -0.08% a year, Irish-domiciled, accumulating. Fund B: OCF 0.20%, AUM £40m, wider spread, tracking difference of -0.35% a year, newly launched. Fund A is the better-built product on almost every axis despite both "tracking the S&P 500." This is the kind of side-by-side the fact sheet makes possible once you know where to look.

Domicile preview. For non-US investors, the domicile line is not a footnote. An Ireland-domiciled UCITS S&P 500 ETF typically suffers 15% US dividend withholding tax, while a Luxembourg one may suffer more, a gap that shows up in tracking difference. We dedicate a full article to domicile and tax later, but train your eye to find that line now.

Common mistakes

• Choosing on OCF alone. A slightly cheaper fund with worse tracking, a wider spread, or unfavourable domicile can cost more in practice. Compare total cost and multi-year tracking difference.
• Ignoring the spread. For frequent or large trades, the bid-ask spread can dwarf the annual fee. Always check it before trading.
• Mistaking volume for liquidity. Underlying-asset liquidity is what lets big orders fill near fair value. Don't dismiss a low-volume fund that holds liquid assets.
• Overlooking fund size. Very small funds can close, forcing an untimely sale. Favour established, adequately sized funds unless you have a specific reason not to.
• Skipping the holdings list. The fact sheet's top-ten holdings reveal concentration the fund's name may hide. Always glance at what you actually own.
• Reading KID scenarios as predictions. They are standardised models, not forecasts. Use them to compare funds, not to set expectations.

FAQ

What is a good expense ratio for an ETF? For a broad-market index ETF, anything from roughly 0.03% to 0.20% a year is competitive; the cheapest large trackers sit near 0.03–0.07%. Specialist, thematic, or active ETFs cost more, sometimes 0.5% or above.

What does AUM tell me? It signals scale and viability. Larger funds tend to be cheaper, more liquid, and less likely to close. Very small funds carry closure risk.

Where do I find an ETF's fact sheet and KID? On the issuer's website (BlackRock/iShares, Vanguard, etc.) and usually on your broker's fund page. The KID is a legally required, standardised document for UK and EU investors.

Why does my tracker lag the index? Mainly the fee, plus smaller effects like cash drag, rebalancing costs, and withholding tax on foreign dividends. A gap close to the OCF is normal and expected.

The takeaway

A fact sheet turns "they all track the same index" into a set of answerable questions: how much does it cost in total, how big and viable is it, how tightly does it track, how does it replicate, and where is it domiciled? Train your eye to find the OCF, AUM, spread, tracking difference, replication method, and domicile, and you can separate a well-built fund from a well-marketed one in under a minute. With evaluation skills in hand, the next article surveys the full landscape of ETF types, from broad-market to thematic, bond, and commodity funds.

Educational not advice

This article is for general educational purposes only and is not financial, investment, or tax advice. Figures are illustrative. Fund costs, sizes, and tracking records change over time and should be verified on current documents. Investing carries risk, including loss of capital. Consider advice from a regulated professional.

Sources

• ESMA / FCA, PRIIPs KID requirements and methodology
• Morningstar, ETF cost, tracking difference, and liquidity research (2026)
• BlackRock iShares and Vanguard, fund fact sheets and KIDs
• ETFGI, fund-size and closure-rate data