Bid–ask spreads often widen during market volatility because offering an immediate trade becomes riskier. Prices can move against a liquidity provider before it can offset a position, while new information can make an existing quote out of date. Some participants respond by quoting wider prices; others reduce the amount they are willing to trade.
For traders, that means the price move on a chart is only part of the story. Entering or exiting a position may also become more expensive. The basic bid–ask spread still means the difference between the highest quoted buying price and the lowest quoted selling price. What changes during volatility is the compensation participants demand for trading now.
Price volatility and spread widening are different changes
Volatility describes price fluctuations. The spread describes the distance between buying and selling quotes at a particular moment. They often change together, but they measure different things.
Suppose a stock moves from a $50.00 bid and $50.02 ask to a $51.00 bid and $51.02 ask. Its price has risen, but its quoted spread remains two cents. If the quotes instead become $50.90 and $51.10, the spread has widened to twenty cents.
This distinction matters when reviewing a trade. A worse entry price may reflect a movement in the market, a wider spread, or both. Looking only at the last traded price cannot separate those effects. Compare the bid and ask at the time of the decision, rather than treating a chart price as an executable offer.
Why liquidity providers demand more room
Holding a position becomes riskier
A market maker that buys from a seller may need to hold that position until another buyer arrives, or hedge it through a related instrument. During that interval, the market can move against it. Larger potential price swings increase the risk attached to the same position.
Hedging does not make that exposure free. If the hedge becomes more expensive or harder to execute, the original trade becomes less attractive. Wider quotes can compensate for these costs. Risk controls can also prompt dealers to reduce positions or scale back trading, connecting inventory risk, hedging costs and wider market-making spreads.
Consider a hypothetical dealer buying at $99.99 with the intention of selling near $100.01. A two-cent difference offers little protection if the price drops twenty cents before the next sale. The dealer might lower its bid, raise its ask, reduce its quoted size, or combine those responses.
Existing quotes can become stale
New information creates another problem: someone may trade against a quote before its owner updates it. A seller offering stock at $100 could be caught at an outdated price if news suddenly makes buyers willing to pay $101.
This is adverse selection: the risk of trading with a counterparty whose information or interpretation is better than yours. It need not involve confidential information. A faster response to a public announcement can be enough. Electronic liquidity providers manage this exposure through quote updates, smaller sizes and other controls examined in BIS research on electronic trading and liquidity provision.
In the hypothetical example, moving the ask farther away buys protection against selling too cheaply. Lowering the bid provides protection against buying too dearly. The resulting spread can widen even before much trading occurs.
The best available quotes can disappear
A quoted spread can also widen without any participant deliberately increasing its own two-sided spread. If the best buying order is cancelled or filled, the next available bid may be lower. If the cheapest selling order disappears, the next ask may be higher.
Suppose the best bid is $49.99, with another buyer waiting at $49.95. Removing the first order lowers the best bid by four cents. If the ask stays unchanged, the displayed spread widens by the same amount.
This is why spread and depth should be assessed together. The spread shows the distance between the best prices; depth shows the quantity available at those prices and beyond them. The broader relationship between liquidity and bid–ask spreads helps explain why an apparently attractive quote may offer little capacity for a larger order.
Why announcements can cause sudden spread changes
A scheduled release fixes the time information arrives, not what that information will say. Participants may know an announcement is coming and still disagree sharply about its outcome or implications.
There can therefore be a short period in which prices adjust quickly while participants hesitate to offer firm trading prices. Historical evidence from the Treasury market shows that spreads widened sharply around major announcements, while the surge in trading volume followed after a delay. The sequence appears in New York Fed research on price formation around announcements.
For an execution decision, the practical question is not simply whether the announcement has been published. It is whether the available prices and quantities now support the intended trade.
Suppose quotes remain unusually far apart after a release. Waiting for a fixed number of seconds would be an arbitrary response unless that waiting period is part of a tested process. A more useful check is whether the spread has settled, sufficient quantity is available and the trade still makes sense at the executable price. Waiting also carries a cost: the market may move away.
A worked example of a wider spread
The following hypothetical quotes keep the midpoint at $50.00 so that the effect of spread widening can be separated from a directional price move.
| Condition | Bid | Ask | Spread per share | Immediate buy-and-sell loss |
|---|---|---|---|---|
| Narrower quotes | $49.99 | $50.01 | $0.02 | $20 |
| Wider quotes | $49.90 | $50.10 | $0.20 | $200 |
Buying 1,000 shares at $50.10 and immediately selling them at $49.90 produces a $200 loss. The midpoint has not moved. The entire difference comes from crossing the wider spread.
Do not double that figure simply because the example contains a purchase and a sale. At unchanged quotes, that immediate round trip costs one full spread. Relative to the midpoint, the purchase costs half the spread and the sale costs the other half. The distinction is covered further in calculating the bid–ask spread.
A wider spread can also affect an existing position. In this example, the quoted selling value of 1,000 shares falls by $90 when the bid drops from $49.99 to $49.90, despite the unchanged midpoint. That is a change in the available exit quote, not evidence that the midpoint fell by nine cents.
Real trades will not necessarily match this tidy example. Quotes may move between entry and exit, and the full order may not execute at the best displayed price.
Why heavy trading does not guarantee a narrow spread
Trading volume records completed transactions. It does not tell you how much additional buying or selling the market can absorb at its current prices.
A busy market can still have poor liquidity. During March 2020, Treasury trading activity was high even as spreads widened, quoted depth declined and trades had greater price impact. The thirty-year bond spread reached more than six times its post-crisis average in the New York Fed study of Treasury liquidity during the COVID-19 crisis.
The distinction is easier to see with a hypothetical order book. A market could complete thousands of small trades while offering only 100 shares at the best ask at any instant. A trader wanting 5,000 shares should not assume that high recent volume makes the entire order available at that price.
For the same reason, avoid interpreting a burst of activity as automatic evidence that trading conditions have recovered. Check the price, the available quantity and the cost of completing the intended order. Volume answers a different question.
Does every volatility spike widen the spread?
No. Volatility creates reasons for spreads to widen, but the result is not a fixed formula. A market can reprice rapidly without a proportionate increase in the distance between its best quotes.
Research published in 2018 examined USD/CAD responses to selected surprising Bank of Canada policy announcements. It found higher exchange rate volatility but only a modest increase in spread costs. That Bank of Canada study of announcement volatility and transaction costs provides a useful counterexample to the claim that faster price movement must produce much wider spreads.
Keep the measures separate in your own analysis. Record price movement, quoted spread and available size rather than using any one of them as a substitute for the others. “Volatile” is a description of price behavior, not a complete execution assessment.
What to check before placing an order
Separate the spread from slippage
The spread is the gap between simultaneous bid and ask quotes. Slippage is the difference between a chosen reference price and the eventual execution price. A trade can face a wide spread without additional slippage, or experience slippage even when the initial spread looks narrow.
Suppose the ask is $50.10 when you submit a purchase, but the order executes at $50.18. The extra eight cents is not another measurement of the original spread. Keeping spread costs separate from slippage makes execution records more useful and avoids counting the same cost twice.
Choose the reference price before reviewing the result. Comparing a fill with an earlier chart price mixes more effects together than comparing it with the executable quote available at submission.
Decide whether price or immediacy matters more
A market order seeks immediate execution without setting a price boundary. A limit order sets a maximum purchase price or minimum sale price, but may remain unfilled. A conventional stock stop order becomes a market order once triggered, so its stop price is not a guaranteed execution price. These distinctions appear in the SEC investor explanation of order types.
A hypothetical buy limit at $50.12 would prevent execution above that price, but it would not guarantee the desired quantity. If offers move beyond the limit, some or all of the order could remain open. Price control and certainty of completion are different objectives.
Before submitting an order during volatile conditions, ask:
- What are the current bid and ask, rather than the last traded price?
- How much would the quoted spread cost for the intended quantity?
- Is sufficient quantity available near the desired price?
- Would an unfilled order be preferable to execution beyond a defined price?
Use those answers to reassess the trade, not just the order button. If the expected benefit depends on a small price move, a wider spread may consume too much of it. If reducing an existing exposure is the priority, waiting for cheaper execution carries its own risk.
Bid–ask spreads widen when the terms for supplying immediate liquidity become less attractive. The useful response is to measure those changed terms: executable prices, available quantity and acceptable execution cost. A price forecast alone does not settle whether the trade is worth making.