How Do You Compare Bid-Ask Spreads Across Similar ETFs?
Two exchange-traded funds can track nearly identical exposures and still cost noticeably different amounts to trade, simply because of how easily their shares change hands.
The short answer
The bid-ask spread is the gap between the highest price a buyer is willing to pay for a share and the lowest price a seller is willing to accept. A narrower spread means it’s cheaper to buy or sell; a wider spread means the act of trading itself eats into returns. Comparing spreads across similar ETFs, especially at the times and sizes an investor actually plans to trade, helps reveal a real cost that the expense ratio doesn’t capture.
Why spreads differ between similar funds
Spreads are shaped by trading activity and by how easily market makers can manage the risk of holding shares of a fund. A fund with high average trading volume tends to have a tighter spread, because more buyers and sellers are active and market makers face less risk holding inventory. A fund that trades less often, even one tracking a similar or identical index to a more popular counterpart, can carry a noticeably wider spread simply due to lower interest, not because anything is wrong with the fund itself.
The underlying holdings matter too
An ETF’s spread isn’t purely about the ETF’s own trading volume — it also reflects how liquid the fund’s underlying holdings are. A fund holding widely traded large-company stocks can typically be created and redeemed efficiently, which helps keep its spread tight even if the fund itself doesn’t trade heavily. A fund holding less liquid securities, such as certain bonds or smaller companies, may have wider spreads regardless of the ETF’s own trading volume, because the underlying market itself is less liquid.
How to actually compare spreads
- Check spreads at different times of day. Spreads are often wider near market open and close and tighter during the middle of the trading day.
- Look at the spread relative to price, not just in absolute terms. A one-cent spread means something different on a $20 share than on a $200 share.
- Consider trade size. Placing a very large order relative to a fund’s typical volume can move the price more than the quoted spread suggests.
- Compare over multiple days, not a single snapshot. A spread observed once may not represent the fund’s typical trading conditions.
Why this matters more for some investors than others
For someone making a single purchase and holding for years, a modest difference in spread is a minor, one-time cost. For someone who trades more frequently, or who trades in large size relative to a fund’s typical volume, spread differences can accumulate into a meaningful drag over time. This is part of the broader total cost of ownership of a fund, distinct from its stated expense ratio.
What to weigh
Spread isn’t fixed — it shifts with market conditions, time of day, and overall trading activity. Rather than treating a single observed spread as definitive, looking at it over time and relative to trade size gives a more realistic sense of what trading a particular fund is likely to cost in practice.