3. One company and its price

The best bid and ask over time (QR)

QR (quote recap) shows every change in the best bid and ask across US exchanges, with sizes, venues and the spread in basis points.

  • 5 min
  • 3 questions
  • Lesson 2 of 2

Why you would care

How much does it cost to trade this stock right now, and is that normal? The spread is a cost you pay on every trade (chapter 01, Reading a quote). It is small for big stocks, but it widens before the open, after news, and in thin names. QR shows that cost moment by moment, so you know whether now is a cheap or an expensive time to trade.

The idea from scratch

Each exchange shows its own best bid and best ask. The NBBO (national best bid and offer) is the best of all of them at one moment:

  • the national best bid: the highest bid on any exchange,
  • the national best offer (ask): the lowest ask on any exchange.

US rules require brokers to give customers a price at least as good as the NBBO, so it is the reference price of the whole market.

Spread in basis points

To compare spreads across stocks with different prices, traders use basis points (bp): 1 bp = 0.01%.

Locked and crossed

  • Locked

    the best bid equals the best ask on two different exchanges. Brief and rare during the day.

  • Crossed

    the best bid is above the best ask. A glitch or a race; it should vanish in a moment.

Both show up more often outside the regular session.

Sizes: read them as shares

Since November 2025, US exchanges report quote sizes in shares, rounded down to whole round lots. A round lot is the standard block of shares, set by the stock's price:

Share priceRound lot
up to $250100 shares
$250 to $1,00040 shares
$1,000 to $10,00010 shares
above $10,0001 share
Diagram: Nasdaq: bid 332.54, ask 332.66 leads to NBBO = best bid 332.55 + best ask 332.64; EDGX: bid 332.55, ask 332.70 leads to NBBO = best bid 332.55 + best ask 332.64; Arca: bid 332.50, ask 332.62 then 332.64 leads to NBBO = best bid 332.55 + best ask 332.64; NBBO = best bid 332.55 + best ask 332.64 leads to Spread 0.09 = about 2.7 bp.
Wide diagram: scroll sideways to see all of it.

(Illustrative quotes, close to the screenshot.)

See it in Gloom

Gloom screenshot: QR AAPL before the US open on 2026-10-06
QR AAPL before the US open on 2026-10-06: summary on top, then one row per NBBO change with bid, size, venue, ask, size, venue and spread. 15 minutes delayed. Historical example.

open ittype QR AAPL, or open TAS AAPL and switch to the NBBO tab.

  1. Spread 2.71 bp median: half the time the spread was narrower, half wider. Very cheap to trade.
  2. Widest 10.52 bp: the worst moment in the window.
  3. Locked 6 or crossed: six moments where bid and ask touched or crossed (premarket).
  4. The first row: bid 332.55 for 960 shares on EDGX; ask 332.64 for 40 shares on venue G; spread about 2.7 bp.
  5. Rows lower down: at 08:48:21.748 the ask improved to 332.62 on Arca and the spread narrowed to between 1.5 and 2 bp.
  6. Footer: 15m delayed, the time of the snapshot.

Practice and recap

Try it3 tasks
  1. Compute the spread at the first row in dollars and bp. (332.64 - 332.55 = 0.09; 0.09 / 332.6 x 10,000 = about 2.7 bp.)
  2. Which venue held the best bid in most rows? (EDGX.)
  3. Would you rather trade at the median spread or the widest one? Why does premarket see the widest?
Common mistakes4 mistakes
  • Comparing spreads in dollars between a 10-dollar and a 1,000-dollar stock. Use bp.
  • Assuming the NBBO is the price for any size. It is the price for the size shown.
  • Panicking at a crossed quote. It is usually a split-second glitch.
  • Forgetting that the free plan shows the tape 15 minutes late.
Check yourself3 questions
  1. What does NBBO stand for, and what is it?
  2. Bid 50.00, ask 50.05. Spread in bp?
  3. What is a locked market?
Answers
  1. National best bid and offer: the highest bid and lowest ask across all US exchanges at one moment.
  2. 0.05 / 50.025 x 10,000 = about 10 bp.
  3. The best bid equals the best ask, on two different exchanges.
Words in this lesson6 words
NBBO
National best bid and offer: the best bid and ask across all US exchanges.
midpoint
Halfway between bid and ask.
basis point (bp)
0.01%; spreads are often quoted in bp of the midpoint.
locked market
Best bid equals best ask.
crossed market
Best bid above best ask.
round lot
The standard block of shares, 100 below $250 and fewer above.

Educational material about reading market data, not investment advice.