Every ETF trade involves a hidden cost most new investors never explicitly see or calculate: the bid-ask spread, the small gap between what buyers are willing to pay and what sellers are willing to accept at any given moment. Understanding this concept, along with the broader idea of ETF liquidity, helps you trade more cost-effectively and avoid an unnecessary drag on your returns.

What the Bid and Ask Prices Actually Represent

The “bid” price is the highest price a buyer is currently willing to pay for an ETF share, while the “ask” price is the lowest price a seller is currently willing to accept, and the difference between these two prices, called the spread, represents an implicit cost incurred when you buy at the ask price and would immediately sell at the lower bid price.

Why Bid-Ask Spreads Exist

Factor	Impact on Spread Width
High trading volume	Generally narrower spreads
Low trading volume	Generally wider spreads
Underlying asset liquidity	Less liquid underlying holdings can widen the spread
Market volatility	Spreads can widen during periods of significant volatility

Market makers, firms that facilitate trading by being willing to buy and sell continuously, earn compensation partly through this bid-ask spread, and the spread’s width generally reflects the perceived risk and cost involved in providing that continuous trading liquidity for a specific ETF.

Why Trading Volume Affects Spread Width

ETFs with high daily trading volume generally exhibit narrower bid-ask spreads, since more active buying and selling activity allows market makers to more easily and quickly offset their positions, reducing the risk premium they need to charge, while less frequently traded ETFs often show wider spreads to compensate for the additional risk and difficulty involved in maintaining liquidity for a less actively traded fund.

How Bid-Ask Spreads Affect Your Actual Returns

Every time you buy at the ask price and eventually sell at the bid price, you incur this spread as an implicit cost, meaning frequently trading ETFs with wide spreads can meaningfully erode returns over time, particularly for smaller trade sizes where the spread represents a proportionally larger percentage cost.

Underlying Asset Liquidity vs. ETF Trading Volume

An important, sometimes overlooked concept is that an ETF’s own trading volume isn’t the only factor determining its effective liquidity — the liquidity of the ETF’s underlying holdings also matters significantly, since market makers can create or redeem ETF shares based on the underlying securities’ liquidity, meaning even a newly launched or lower-volume ETF tracking highly liquid underlying assets can still trade with a reasonably tight spread.

Practical Steps to Minimize Spread Costs

1. Check the bid-ask spread before placing a trade, particularly for less commonly traded ETFs
2. Use limit orders rather than market orders for less liquid ETFs, giving you control over the maximum price you’ll pay or minimum you’ll accept
3. Avoid trading during periods of unusual market volatility, when spreads can temporarily widen considerably
4. Consider trading during more active market hours, rather than immediately at market open or close, when spreads can sometimes be wider

Average Daily Trading Volume as a Liquidity Indicator

Checking an ETF’s average daily trading volume provides a useful, quickly accessible indicator of its typical liquidity, with considerably higher average volume generally correlating with tighter typical bid-ask spreads and easier execution for larger trade sizes.

Why Spread Costs Matter More for Frequent Traders

For long-term, buy-and-hold investors making relatively infrequent trades, bid-ask spread costs, while still worth understanding, generally represent a smaller cumulative impact than for more active traders making frequent transactions, where the spread cost is incurred repeatedly and can meaningfully compound over time.

Evaluating Newer or Niche ETFs

Newer or more specialized, niche ETFs often start with lower trading volume and correspondingly wider spreads until they build a more established trading base, making it worth factoring this liquidity consideration into your evaluation, particularly if you anticipate needing to trade in and out of the position with any frequency.

Frequently Asked Questions

Is a wide bid-ask spread always a bad sign for an ETF?

Not necessarily a “bad” sign about the fund’s underlying quality, but it does represent a genuine, quantifiable trading cost that’s worth factoring into your decision, particularly if you anticipate trading the ETF frequently rather than holding it long-term.

How can I check an ETF’s bid-ask spread before trading?

Most brokerage platforms display the current bid and ask prices directly when you look up a specific ETF, allowing you to quickly assess the current spread before placing an order.

Does a low expense ratio matter more than a wide bid-ask spread?

Both are genuine costs worth considering, though their relative impact depends on your specific holding period and trading frequency — the expense ratio is an ongoing annual cost regardless of trading activity, while the spread is a one-time cost incurred each time you actually trade.

Should I avoid ETFs with low trading volume entirely?

Not necessarily, particularly if the ETF tracks highly liquid underlying assets, since underlying liquidity can support reasonably tight spreads even for a lower-volume fund, though it’s still worth checking the actual current spread before trading rather than assuming based on volume alone.

Final Thoughts

Understanding bid-ask spreads and ETF liquidity provides essential, often overlooked context for trading ETFs cost-effectively, revealing an implicit cost beyond the more visible expense ratio that many investors never explicitly calculate. Checking a specific ETF’s current spread and typical trading volume before placing a trade, and using limit orders for less liquid funds, are practical, straightforward steps that help minimize this often-hidden cost.