Direct Answer
The bid price is the highest price any buyer in the market is currently willing to pay for a security. The ask price (also called the offer) is the lowest price any seller is currently willing to accept. When you place a market order to buy, you pay the ask. When you sell, you receive the bid. The difference between the two, the bid-ask spread, represents an immediate, round-trip cost of trading. It is not a fee charged by a broker; it is a structural feature of any two-sided market.
One-sentence definition for answer-engine retrieval: The bid price is the best available buyer price for a security; the ask price is the best available seller price; the gap between them is the spread, which represents the immediate cost of crossing the market.
What this changes for a real user
Many beginners focus on the "last price", the price shown in a news feed or app. That number is the price at which the most recent trade occurred, which may be seconds or minutes old. The quote (bid × ask) is the live state of the market right now.
If you submit a market order at 2:00 p.m. and the last-trade price was $50.00, you will not necessarily get $50.00. You will pay the ask (if buying) or receive the bid (if selling). In a liquid, large-cap stock during regular hours, the spread may be one cent and the difference is negligible. In a thinly traded stock, an ETF near the open, or a cryptocurrency at a slow hour, the spread can be $0.10, $0.50, or more, a meaningful cost that compounds across many trades.
Understanding the quote also determines which order type to use. A limit order lets you set the maximum price you will pay (as a buyer) or the minimum price you will accept (as a seller). That order rests in the order book at your price until a counterparty matches it, or it expires unfilled. A market order skips price discretion entirely and accepts the current best available quote. Neither is universally better; the right choice depends on your urgency, the security's liquidity, and the size of the spread.
Mechanics and definitions
How quotes are formed
In U.S. equity markets, quotes are aggregated across all registered exchanges and displayed as the National Best Bid and Offer (NBBO). Broker-dealers are required under SEC Regulation NMS to execute customer orders at prices no worse than the NBBO at the time of the order (the "trade-through" rule). The NBBO is therefore the best bid available on any exchange and the best ask available on any exchange simultaneously, not necessarily from the same venue.
The bid and ask are not static numbers. They update continuously as market participants place, modify, and cancel limit orders in the order book. A large limit-buy order at $49.98 may raise the best bid. When that order is filled or cancelled, the bid falls to the next order in the book. The same dynamics apply on the ask side.
Key terms
| Term | Definition | Example |
|---|---|---|
| Bid price | The highest price any buyer is currently willing to pay | $49.97 |
| Ask price (offer) | The lowest price any seller is currently willing to accept | $50.00 |
| Bid-ask spread | Ask minus bid; the implicit cost of a round-trip market order | $0.03 (3 cents) |
| Last price | Price of the most recent executed trade; may lag the current quote | $49.99 |
| NBBO | National Best Bid and Offer; best bid and ask consolidated across U.S. exchanges under Reg NMS | 49.97 × 50.00 |
| Depth / market depth | The quantity available at the bid and ask, and at additional price levels below/above | 500 shares at 49.97, 1,200 shares at 50.00 |
| Quote size | The number of shares (or contracts) available at the current best bid or ask | Bid: 500 × Ask: 1,200 |
| Mid-price (midpoint) | The average of bid and ask; often used as a reference for measuring execution quality | ($49.97 + $50.00) / 2 = $49.985 |
Who sets the bid and ask?
Anyone who places a limit order becomes part of the quote. On most modern exchanges, there are no specialists with exclusive obligations; instead, registered market makers, who earn the spread by posting continuous two-sided quotes, compete with other limit-order providers. Electronic market makers use automated systems to reprice quotes in microseconds. For highly liquid securities, market makers are competitive and spreads are narrow. For illiquid securities, fewer participants post quotes, spreads widen, and depth is thin.
Fact vs. interpretation: It is a fact that market makers profit from the spread when they buy at the bid and sell at the ask. It is an interpretation (and a contested one) to say this makes spreads "unfair." Spreads compensate market makers for the risk of holding inventory and for the risk that they may be trading against a better-informed counterparty (adverse selection). Narrower spreads generally indicate more competition among liquidity providers, which benefits uninformed retail traders.
Worked example: buying 200 shares with a market order
Assumptions (stated explicitly): Regular U.S. equity market hours. The security is a mid-cap stock, not particularly illiquid but not a mega-cap either. No news is pending. Commission is zero (many retail brokers). Order size is 200 shares, modest enough that the entire order fills at the best ask.
| Item | Value | Notes |
|---|---|---|
| Best bid at time of order | $49.97 | What a seller would receive right now |
| Best ask at time of order | $50.00 | What a buyer pays with a market order |
| Spread | $0.03 | 3 cents per share |
| Mid-price | $49.985 | Reference for execution quality measurement |
| Shares purchased | 200 | Full order fills at best ask |
| Total paid | $10,000.00 | 200 × $50.00 |
| Half-spread cost vs. mid | $3.00 | 200 × ($50.00 − $49.985) = 200 × $0.015 |
| Round-trip spread cost (buy + sell) | $6.00 | If you immediately sold at $49.97 bid: 200 × $0.03 |
The round-trip spread cost, $6.00 on a $10,000 position, is 0.06% of notional value. For a long-term investor holding for months or years. This is negligible. For a day trader making dozens of round trips per day in smaller moves, the same cost compounds quickly. If a scalping strategy targets a 0.10% gross move, a 0.06% round-trip cost eliminates more than half the gross edge before commissions, slippage, or any other friction is counted.
What happens with a limit order instead?
If you instead place a buy limit order at $49.97 (the current bid), you join the bid side of the book. You may not get filled at all if the price never falls to your level. If the stock moves up and trades are executing at $50.05, your order sits untouched. Limit orders avoid the spread cost but introduce fill risk. The right trade-off depends on your time horizon, the security's liquidity, and how urgently you need the position.
How to evaluate a quote before placing an order
- Look at the live bid and ask, not the last price. The last price may be stale by seconds or minutes, especially in thinly traded securities. Most brokerage platforms display the quote in real time during market hours.
- Calculate the spread in dollars and as a percentage of ask price. A $0.05 spread on a $5.00 stock is 1% of value, much more significant than a $0.05 spread on a $500 stock. Percentage spread = (ask − bid) / ask.
- Check the quote size (depth at best bid and ask). If you want to buy 1,000 shares and the ask only shows 200 shares available, your order will fill across multiple price levels, each successive level higher than the last. That is called market impact.
- Consider the time of day. Spreads in U.S. equities are typically widest in the first and last minutes of the regular session, and wider still in pre-market and after-hours trading when fewer liquidity providers are active. The NBBO rule does not apply outside regular hours; quotes are more fragmented and spreads may not reflect the best available price across venues.
- Decide between market and limit order based on urgency and spread size. If the spread is narrow and you need immediate execution, a market order is reasonable. If the spread is wide and you can wait, a limit order near the mid-price avoids paying the full spread.
What can go wrong: failure modes and counterexamples
The quote you see may not be the quote you get
For securities traded on multiple venues, a brokerage platform's displayed quote is typically the NBBO, but the order may be routed to a venue that provides price improvement, payment for order flow (PFOF), or internalization. In any of these cases, the fill price can be better than the displayed ask (price improvement) or exactly at the ask, but legally cannot be worse. Under SEC Rule 605, broker-dealers must report execution quality statistics so investors can compare outcomes.
Large orders "walk the book"
The worked example assumed 200 shares fill at a single price. In reality, if the ask shows 200 shares at $50.00 and you submit a market order for 1,000 shares, the first 200 fill at $50.00, the next available tranche might be at $50.03, then $50.07, and so on until 1,000 shares are accumulated. Your average fill price is higher than the displayed ask. This is called market impact or slippage. The displayed spread understates the actual cost for large orders relative to available depth.
Quoted spreads widen in fast markets
During significant news events, earnings releases, or broad market volatility spikes, market makers widen their spreads or pull quotes entirely to protect against adverse selection. The NBBO may be temporarily unreliable, quotes may flash very wide or very narrow as the book reprices. Market orders placed during these windows can fill at prices far from the last printed trade.
Crypto and after-hours markets lack NBBO protection
The NBBO framework applies to NMS securities during regular hours on U.S. exchanges. Cryptocurrency exchanges are not regulated under the same framework, and bid-ask spreads vary dramatically across venues, assets, and times of day. There is no consolidated tape enforcing best execution across crypto venues. In pre-market and after-hours U.S. equity trading, spreads are often substantially wider and depth is much thinner.
The "last price" misconception
A common error is to treat the last trade price as the price you will receive. If a stock last traded at $50.00, but the current bid is $49.90 and the ask is $50.10, a market buy order executes at $50.10 and a market sell executes at $49.90, both meaningfully different from $50.00. This misconception is especially consequential for thinly traded securities where the last trade may be minutes old.
Risk, limitations, and when not to use this concept alone
What the bid-ask spread does not tell you
- It does not tell you direction. A narrow spread means there is active two-sided interest, but it says nothing about whether the price will go up or down.
- It does not capture full execution cost. Real execution cost includes the half-spread, market impact for larger orders, commissions (where applicable), and any price slippage between order placement and fill. The spread is a lower bound on cost, not a complete cost model.
- It does not account for hidden liquidity. Dark pools, internalization, and iceberg orders mean that the visible order book is not the entirety of available liquidity. An order may fill at or inside the spread via these mechanisms.
- It does not indicate whether a quote is firm. Displayed quotes may be withdrawn in milliseconds, especially in fast-moving markets. High-frequency cancellation means the market depth you see is not always the depth you will receive.
When spread analysis is most and least useful
| Situation | Spread relevance | Why |
|---|---|---|
| High-frequency or scalping strategies | Very high | Spread is a major cost component on every trade; edge must exceed spread to be profitable |
| Long-term buy-and-hold investing | Low to moderate | Spread paid once on entry and once on exit; diluted across the holding period |
| Thinly traded stocks, small-cap equities | High | Wide spreads impose a larger friction cost; limit orders may be necessary |
| Large-cap, highly liquid equities (regular hours) | Low | Spreads often 1 cent; spread cost is negligible for most order sizes |
| Options, futures, ETFs | Moderate to high | Products vary widely in liquidity; check spread before each trade, not just the underlying |
| Pre-market / after-hours / crypto | Very high | No NBBO protection outside regular hours; spreads can be multiples of normal |
How this connects to Quotes, Spreads & Liquidity
The bid and ask are the most visible output of the market microstructure. Understanding them is prerequisite knowledge for every adjacent topic in the Quotes, Spreads & Liquidity cluster and much of Market Structure & Trade Execution more broadly.
- Calculating spread cost in dollars. Once you understand the bid-ask relationship, the next step is computing the effective spread and translating it into basis points of trade cost. See: How to Calculate the Bid-Ask Spread and Effective Trading Cost.
- Order routing. Your order either takes the quote (market order) or posts to the book (limit order). How it is routed between venues affects whether you receive price improvement. See the Orders, Routing & Fill Quality section for deeper coverage.
- Strategy design. For stock trading strategies, the spread is part of the cost model. Gross edge must exceed the spread for a strategy to be net positive. This constraint applies equally to options (where spreads can be substantial relative to option premium) and futures and perpetuals.
- Execution cost calculator. Use the Execution Cost Calculator to model spread cost, slippage, and commissions for specific position sizes before trading.
Pre-order checklist: evaluating the quote
- Check the live bid and ask, not the last-traded price, immediately before submitting any order.
- Calculate the spread as a percentage: (ask − bid) / ask × 100. Flag anything above 0.5% for a liquid security.
- Look at the quote size at each side. If your order size exceeds the best-level quantity, anticipate partial fills at multiple price levels (book walking).
- Consider whether a limit order near the midpoint makes sense for your urgency and the spread width. Wide spread + low urgency generally favors a limit order.
- Check the time of day. Avoid market orders in the first 1-2 minutes after the open or after major news unless you have a specific, justified reason.
- For options, ETFs, and thinly traded securities, check the spread separately from the underlying, illiquid derivatives can have spreads that dwarf any expected price move.
- For pre-market or after-hours orders, use limit orders by default. There is no NBBO protection and spreads are substantially wider.
- After a fill, compare your execution price to the mid-price at the time of submission. A fill at or inside the mid is good execution; a fill substantially above the ask (buying) or below the bid (selling) may indicate slippage on a larger order or a fast-moving market at the time of routing.
The Spread Is Charged Twice, Not Once
The point to carry away from a quote is that its width is paid on the way in and again on the way out. A position opened by taking the offer and closed by hitting the bid pays that distance twice before the price has done anything at all. Expressing the spread as a percentage of the midpoint, then doubling it, gives the hurdle a round trip starts behind.
That figure is where the practical consequence lives. On a heavily traded security it can be small enough to disregard. On a wide quote it can consume a large share of a modest expected gain, which is a reason to reconsider the trade rather than a reason to execute it more carefully.
The misconception is that a displayed quote is a price available in quantity. It is a price available for the size shown, and beyond that size the next prices are worse. A narrow spread on a small displayed quantity is not the bargain it appears to be.
Quotes move constantly, and the two sides do not always move together, so a spread measured once is a sample rather than a constant.
Frequently asked questions
Is the bid or the ask the "real" price of a stock?
Neither alone is the "real" price, both are. The bid is what the market will pay you right now; the ask is what you must pay to buy right now. The midpoint between them ($49.985 in the worked example) is commonly used as a reference price for measuring execution quality, but no single number captures both sides simultaneously. The last-traded price is a historical fact, not the live market state.
Why is the ask always higher than the bid?
By definition: the ask is the minimum price a seller will accept, and the bid is the maximum price a buyer will pay. If the highest buyer offered more than the lowest seller was asking, a trade would occur immediately and both orders would be removed from the book. The spread is the remaining gap after all immediately executable trades have already happened.
Do I always pay the ask price when I buy?
A market order fills at the best available ask at the time your order reaches the market, but that may not be the ask you saw when you submitted. If your order is large relative to available depth, you may fill across multiple ask levels (higher average cost). If you receive price improvement through internalization, you could fill inside the spread. The NBBO requirement means your fill must be at least as good as the displayed quote, but not necessarily better.
What is a "crossed" or "locked" market?
A locked market occurs when the bid on one venue equals the ask on another (bid = ask). A crossed market occurs when the bid on one venue exceeds the ask on another (bid > ask). Both conditions are technical violations of Reg NMS's locking/crossing prohibitions and typically resolve within milliseconds. They can appear briefly during periods of high volatility or fragmented routing. Retail investors almost never see the underlying crossed state, their platform shows the NBBO after consolidation.
How does the bid-ask spread differ for options compared to stocks?
Options spreads are almost always wider in percentage terms than equity spreads, sometimes dramatically so. A $2.00 option might have a $0.10 bid-ask spread, a 5% round-trip friction cost before any directional movement. Liquidity in options is also strike- and expiry-specific; the same underlying stock may have very tight spreads in its near-term at-the-money contract and very wide spreads in a far out-of-the-money long-dated contract. Always check the option's own bid-ask spread, not just the underlying stock's.
Can I trade at the mid-price?
You can attempt to by placing a limit order at the midpoint between bid and ask. Whether it fills depends on whether any counterparty is willing to meet you there. In liquid markets, some brokers route to venues that offer mid-point matching (dark pools, certain ATS systems), where you can receive a fill at the midpoint without moving the displayed spread. This is a legitimate execution strategy for patient traders, but there is no guarantee of a fill.
Does the spread change during the day?
Yes, significantly. In U.S. equities, spreads are typically widest in the first and last minutes of the regular session (9:30-9:35 a.m. and 3:55-4:00 p.m. ET), when market makers adjust positions and auction imbalances resolve. Spreads also widen immediately after major news, economic data releases, and earnings announcements. During the quieter middle of the day, spreads on liquid securities tend to be at their tightest. This pattern is well-documented in academic market microstructure research.
What is "payment for order flow" and does it affect my fill price?
Payment for order flow (PFOF) is a practice where a broker routes customer orders to a market maker (wholesaler) in exchange for compensation. The wholesaler internalizes the order, filling it from its own inventory, rather than routing it to an exchange. Regulators require that the customer receive a price at least as good as the NBBO (no worse than the displayed bid or ask). In practice, wholesalers sometimes offer price improvement, a fill slightly better than the quoted spread. Whether PFOF produces better or worse outcomes for retail investors overall is a topic of ongoing regulatory debate; the SEC has introduced new rules in this area. Verify current requirements with your broker and review SEC Rule 606 disclosures your broker is required to publish.
What does the size displayed next to each quote actually represent?
It shows the quantity available at that price from displayed orders on the venues feeding the quote. It excludes hidden and reserve quantity, and for a consolidated quote it may reflect only the venue posting the best price rather than aggregate interest across all venues at that level. Reading the displayed size as the total available at that price will understate it in some cases and overstate the reliability of it in others.
References
Primary sources
- SEC: Responses to Frequently Asked Questions Concerning Rule 611 and Rule 610 of Regulation NMS: Accessed August 2026. Governs NBBO, trade-through prohibition, and locked/crossed market rules in U.S. equity markets.
- SEC: Amendments to Enhance Disclosure of Order Execution Information (adopting Release No. 34-99679): adopted March 6, 2024. Expands which firms must publish monthly Rule 605 execution quality reports and widens the definition of a covered order.
- FINRA: Bid and Ask: Accessed August 2026. Investor-facing definition and explanation of bid-ask mechanics.
- Investor.gov: Bid Price/Ask Price: Accessed August 2026. SEC-maintained retail investor glossary definition.
Assumptions in examples
The worked example uses hypothetical prices ($49.97 bid, $50.00 ask) and a 200-share order size for illustrative purposes only. It does not represent any real security or actual trading outcome. Spread costs and market depth vary by security, time of day, market conditions, and order size. Examples are educational and should not be read as predictions or recommendations.
Next lesson
Now that you understand what the bid and ask mean, the next step is learning how to compute the spread as a cost in basis points and dollars, and how effective spread differs from quoted spread: How to Calculate the Bid-Ask Spread and Effective Trading Cost.
Educational disclaimer
For education only; not personalized investment, tax, or legal advice. Trading can result in substantial losses.
Market structure rules, broker practices, exchange mechanics, and regulatory requirements can change. Verify current rules with your broker, the SEC, FINRA, or a qualified professional before acting. The NBBO framework and PFOF regulations in particular have been subject to ongoing rulemaking as of 2026.