ETF Total Cost of Ownership
Why the expense ratio printed on the fact sheet is only part of what an ETF actually costs to hold, and what else — the bid-ask spread, tracking difference, taxes — belongs in a fair comparison.
Prerequisites: Tracking Error vs Tracking Difference, Where Tracking Error Comes From
Two ETFs tracking the same index, both charging a 0.05% expense ratio, are not necessarily equally cheap to own. The expense ratio is the most visible number and the easiest to compare, but it's only one line item in what an investor actually gives up by holding a fund, and a narrow focus on it can hide a fund that's meaningfully more expensive in practice.
The bid-ask spread is the gap between the price you can buy at and the price you can sell at on the exchange, and it's paid every time you trade, not annually — a fund with a wide spread can cost a buy-and-hold investor little, but is expensive for anyone trading it frequently. Tracking difference captures costs the expense ratio doesn't, like cash drag or foreign withholding taxes, and can push effective cost above or below the stated fee. Premiums and discounts to net asset value — the ETF's market price trading away from the value of what it holds, common in thinly traded or hard-to-arbitrage funds — are a real cost if you happen to buy at a premium or sell at a discount. And taxes, particularly the frequency and size of capital gains distributions, differ across funds even at identical expense ratios, especially between ETFs (which typically distribute little thanks to in-kind redemptions) and comparable mutual funds.
Total cost of ownership is the attempt to add all of this up rather than stopping at the expense ratio: for a long-term holder of a large, liquid fund, the expense ratio usually dominates and the rest is noise; for someone trading in and out of a smaller or less liquid fund, spread and premium/discount risk can dwarf the stated fee.
A useful rule of thumb: the expense ratio matters most to the last buyer holding for years, while spread and premium/discount matter most to the first trader entering and exiting quickly. A newly launched, thinly traded ETF might carry a headline expense ratio identical to a decade-old giant tracking the same index, yet cost a trader far more round-trip simply because its spread is ten times wider — the kind of gap a fact sheet never shows but a live quote screen reveals immediately.
The expense ratio is a starting point, not the full cost of holding an ETF. Bid-ask spread, tracking difference, premium/discount to NAV, and tax efficiency all add to or subtract from what a fund actually costs an investor, and which of these matters most depends heavily on how large, liquid, and long-held the position is.
Further reading
- ICI, ETF Handbook, ch. 5