The ask price is the lowest price anyone is currently offering to sell a stock for, and the ask size is how many shares are offered at that price. On a hypothetical quote line reading "ask $50.01, size 200 shares," a buyer could take up to 200 shares at $50.01 while the offer stands. The bid is the best price a buyer is offering, and the gap between them, the spread, is what buying and immediately selling at an unchanged quote costs before fees. Two rule changes matter here: since November 3, 2025, stocks whose average closing price is above $250 have round lots of 40, 10 or 1 share instead of 100, and half-cent quotes that would narrow some spreads were pushed back to November 2027.
Two pointers before the details. If your screen counts size in lots rather than shares, the round-lot section below explains how to read it. And if you came here asking what quote, spread and price guarantee mean in "instant execution," that section answers it directly.
Reading a quote line
Investor.gov defines the bid as "the highest price a buyer will pay to buy a specified number of shares of a stock at any given time" and the ask as "the lowest price at which a seller will sell the stock." The size is the number of shares behind each price; Regulation NMS defines an aggregate quotation size as the sum of the quotation sizes of the brokers or dealers quoting on an exchange "at the same price." Those two prices and two sizes are the core of the quote. The last trade price shown nearby is something else, and Investor.gov adds a caution: "the last-traded price is not necessarily the price at which a market order will be executed."
Before reading the size, check whether your screen counts shares or lots. That matters more than it used to, because the lot itself now depends on the stock.
Ask size now depends on the share price
A round lot is the standard block a quote is measured in: Regulation NMS treats a bid or offer as a price at which someone "is willing to buy or sell one or more round lots." In its 2024 rulemaking the SEC described the old setup: "for most NMS stocks a round lot is defined as 100 shares." The new definition, implemented on the first business day of November 2025 (Nasdaq gave the start date as November 3), assigns each stock a round lot from its average closing price on its primary listing exchange during a one-month evaluation period. September's prices set the round lot that applies from the first business day of November, and March's set the one for May.
Nasdaq's daily symbol directory files carry each security's assigned round lot and pick up new assignments on the last trading day of April and October. I counted the files generated on November 3, 2026, leaving out test issues but keeping ETFs, preferred shares and other listings:
| Round lot | Average closing price | Securities | Examples |
|---|---|---|---|
| 100 shares | $250.00 or less | 12,932 | NVIDIA, Netflix, Ford |
| 40 shares | $250.01 to $1,000.00 | 283 | Apple, Microsoft, SPDR S&P 500 ETF (SPY) |
| 10 shares | $1,000.01 to $10,000.00 | 23 | Eli Lilly, BlackRock, AutoZone |
| 1 share | $10,000.01 or more | 1 | Berkshire Hathaway Class A |
That puts 307 of 13,239 securities, or 2.32%, on something other than a 100-share lot. Berkshire Hathaway sits in two tiers at once: its Class A shares have a one-share round lot and its Class B shares a 40-share lot.
A smaller order can now be a full round lot in a pricier stock. Before the change, a 40-share offer in a stock above $250 was an odd lot, and the SEC noted in 2024 that the consolidated data distributed by the securities information processors (SIPs), the feeds that carry the national best bid and offer, "does not include odd-lot quotation information" unless exchanges aggregate odd lots into round lots. The SEC said the new sizes "will provide transparency about some better priced orders in higher priced stocks," though not for orders still defined as odd lots or for stocks at $250 or less.
Odd lots are getting their own data. In a request letter cited by the SEC, the plan participants said the SIPs would begin publishing the best odd-lot order, meaning the highest odd-lot bid above the national best bid and the lowest odd-lot offer below the national best offer, in May 2026; the fuller odd-lot data was deferred to the first business day of May 2028. Whether that feed is running and whether your broker shows it are separate questions.
The size you see can also be rounded or counted in lots. The rules require the SIPs to show quote sizes as a number of shares, rounded down to the nearest multiple of a round lot, with a compliance date of the first business day of November 2025. In a stock with a 40-share round lot, a hypothetical 130 shares at the best offer would be published as 120: three lots of 40, with the 10 left over not counted in that figure. If your platform shows size in lots instead, an ask size of 4 means four round lots: 400 shares in a stock with a 100-share round lot, but 160 in a 40-share stock such as Apple.
And a thin best offer can raise the average price of a bigger order. If you send a market order for 100 shares and only 40 are available at the best ask, the other 60 may fill at the next, higher offers. The SEC conceded that its package "will increase the likelihood that a 100-share order will walk the book," meaning fill at one price level after another, in stocks affected by both the smaller tick and the new round lots, and answered that those stocks trade above $250, so a 100-share order in them is already worth more than $25,000.
What crossing the spread costs
The midpoint between bid and ask makes a neutral reference point. Buying at the ask pays half the spread above it and selling at the bid gives up the other half, so an immediate round trip at an unchanged quote loses the full spread on every share before commissions or fees. These quotes are hypothetical and assume enough shares at each price.
| Hypothetical quote (bid / ask) | Spread (% of midpoint) | Buy 100 at the ask, vs midpoint | Buy and sell 100 at once |
|---|---|---|---|
| $300.00 / $300.01 | $0.01 (0.0033%) | $0.50 | $1.00 |
| $50.00 / $50.01 | $0.01 (0.02%) | $0.50 | $1.00 |
| $50.00 / $50.05 | $0.05 (0.1%) | $2.50 | $5.00 |
| $9.95 / $10.05 | $0.10 (1%) | $5.00 | $10.00 |
The dollar columns depend only on the spread and the share count, so one cent costs the same $0.50 on the way in for 100 shares in the $50 example and the $300 example. The percentage is where stocks differ: one cent on a $300 stock is about 0.0033% of the midpoint, while ten cents on a $10 stock is 1%, and there the bid has to rise ten cents before a quick sale breaks even. Measured against the cash you paid rather than the midpoint, the numbers shift slightly: the $5.00 round trip on $5,005 spent in the third row is about 0.0999%.
A commission-free account does not remove this cost, as our look at what zero-commission trades can still cost explains. If you also pay a percentage fee, the fee break-even check adds that layer.
Quote, spread and price guarantee in "instant execution"
The phrase "instant execution" comes up on trading platforms such as MetaTrader 5. There the platform attaches its current prices to the order, and the gap between its bid and ask is the spread. MetaTrader's help pages say that in Instant Execution mode "the order is executed at the price offered to the broker": if the broker accepts those prices, the trade goes through. The guarantee has limits. If the price moves during processing by more than the "Deviation" you set, the dealer can refuse the order and offer new prices, valid for only a few seconds, which MetaTrader calls a requote. Within your deviation, the order is filled at the new price without any notice.
A US stock market order does not guarantee the price. Investor.gov says it "guarantees that the order will be executed, but does not guarantee the execution price," and that it "generally will execute at or near the current bid (for a sell order) or ask (for a buy order) price." A limit order flips the trade-off: a buy limit "can only be executed at the limit price or lower," and a sell limit only at the limit or higher, so it caps the price but may never fill. Investor.gov's own example is a buy limit that "will only execute if the price of ABC stock is $10 or lower." In my view, a buyer who wants a price ceiling should look at a limit order at or near the current ask rather than a market order.
For trades outside regular hours, our look at the overnight session Nasdaq and NYSE Arca plan to open in December covers what changes at night.
Half-cent quotes: adopted in 2024, now due in November 2027
Right now, stocks priced at $1.00 or more are quoted in one-cent steps, so the narrowest normal quoted spread is one cent. The SEC's own release says the 2005 penny rule came "at the inevitable cost of introducing a floor, namely one cent, below which the quoted bid-ask spread could not fall." In September 2024 it adopted a change to Rule 612: for quotes of $1.00 or more, a $0.005 increment for a stock whose time-weighted average quoted spread during the evaluation period was $0.015 or less, and $0.01 for the rest. The primary listing exchange would measure that spread over January to March and July to September, with new increments taking effect on the first business day of May and November.
None of that has started. The tick change was stayed, then pushed back twice:
| Date | What happened |
|---|---|
| September 18, 2024 | SEC adopts the half-cent tick, a lower access fee cap and a new schedule for the round lot definition (Release No. 34-101070) |
| December 9, 2024 | The amendments become effective, with later compliance dates |
| December 12, 2024 | SEC stays the tick and fee-cap amendments pending court review; the round lot definition is not stayed |
| October 14, 2025 | The D.C. Circuit denies the petition for review |
| October 31, 2025 | SEC exempts the tick and fee-cap changes until the first business day of November 2026 (Release No. 34-104172) |
| November 3, 2025 | New round lots start, per Nasdaq's trader alert |
| June 11, 2026 | SEC extends that exemption to the first business day of November 2027 (Release No. 34-105656) |
The June 2026 order gave the reason as allowing "an orderly implementation of these Rules in light of other regulatory initiatives scheduled for the balance of 2026." When the change does arrive, its reach could be wide. Using 2023 data, the SEC identified 2,420 NMS stocks with an average quoted spread of $0.015 or less, about 74% of share volume and about 47% of dollar volume, and it expects the smaller increment to let such stocks "quote with tighter spreads." For a stock assigned the half-cent tick, a hypothetical $50.000 / $50.005 quote would cut the cost of buying and selling 100 shares at once to $0.50, from $1.00 at a one-cent spread.
The same package would cut the cap on exchange access fees for stocks priced at $1.00 or more from $0.003 to $0.001 a share, a change delayed on the same timetable. There the SEC expects "lower transaction costs for investors" along with "wider quoted spreads," so a wider posted spread and a lower total cost can arrive together.
My read: the half-cent tick will matter for stocks whose spread already sits near the one-cent floor, and not at all for a stock quoted ten cents wide. Until the first business day of November 2027, plan around one cent as the floor, and check the date on any article that says half-cent quotes are already live.
How to read a quote before trading
The order I'd suggest: work out the spread as a share of the midpoint first, because cents alone hide the difference between a $300 stock and a $10 one. Then set the ask size against the order you have in mind and remember the round lot: in a 40-share stock, a displayed 40 is a single lot, and anything beyond what is available at the best ask may fill higher. When the spread is wide or the size is thin, a limit order at a price you accept caps the cost, with the risk that it does not fill. How long an unfilled order stays live depends on its duration, and our guide to day and good-'til-canceled orders explains when each one expires. And don't count on half-cent quotes before November 2027.
Sources
- SEC · Regulation NMS: Minimum Pricing Increments, Access Fees, and Transparency of Better Priced Orders, final rule, Release No. 34-101070 (Sept. 18, 2024, PDF) — round lot tiers and evaluation period, half-cent tick tiers, access fee cap, the one-cent floor, SIP odd-lot quote data, 2023 count of stocks with spreads of $0.015 or less, expected effects
- Federal Register (govinfo) · SEC order granting temporary exemptive relief, Release No. 34-105656 (June 11, 2026) — adoption history, the December 2024 partial stay, the October 2025 court decision, the October 2025 exemption, and the extension of the tick and fee-cap changes to the first business day of November 2027
- Federal Register (govinfo) · SEC order granting temporary exemptive relief, Release No. 34-104172 (Oct. 31, 2025) — SIPs must show quote sizes in shares rounded down to a multiple of the round lot, compliance date in November 2025
- Federal Register (govinfo) · SEC order on odd-lot information, Release No. 34-104612 (Jan. 15, 2026) — SIPs implemented the round lot definition in November 2025 and planned to start the best odd-lot order in May 2026
- Nasdaq Trader · Equity Trader Alert #2025-76, Nasdaq Reporting Updates for SEC Round Lot Changes (Sept. 30, 2025) — new round lot definitions from November 3, 2025; daily symbol files carry the round lot updates
- Nasdaq Trader · Symbol directory, nasdaqlisted.txt (file created Nov. 3, 2026) — Round Lot Size column for Nasdaq-listed securities; counts and examples in the round lot table
- Nasdaq Trader · Symbol directory, otherlisted.txt (file created Nov. 3, 2026) — Round Lot Size column for securities listed on NYSE and other exchanges; counts and examples in the round lot table
- Investor.gov (SEC) · Bid Price/Ask Price — definitions of bid, ask and spread
- Investor.gov (SEC) · Types of Orders — market orders guarantee execution but not price; limit orders execute only at the limit or better
- MetaTrader 5 Help · Executing Trades — what Instant Execution mode, the Deviation setting and a requote mean on that platform
- Cornell LII · 17 CFR 242.600, Regulation NMS definitions — a bid or offer is for one or more round lots; aggregate quotation size
Editorial note
This article was prepared with the help of AI tools and checked against the sources listed above on 2026-11-03. Worked examples are illustrative unless a source is cited. Read our editorial standards, or tell us if you spot an error.