Three prices answer different questions

The last traded price records a completed transaction. The best bid is the highest displayed buying price; the best ask, also called the offer, is the lowest displayed selling price in the market covered by the quote. ([asic.gov.au](https://www.asic.gov.au/regulatory-resources/markets/market-structure/equity-market-data/quarterly-cash-equity-market-data-release-methodology-and-definitions)) Neither the last price nor a quote guarantees the price of the next transaction. The SEC’s Trading Basics investor bulletin distinguishes the last traded price from a market order’s execution price (see the SEC: Trading Basics investor bulletin reference in Sources). During continuous order-book trading, an immediate purchase generally meets available offers, while an immediate sale generally meets bids. ([asic.gov.au](https://www.asic.gov.au/regulatory-resources/markets/market-structure/equity-market-data/quarterly-cash-equity-market-data-release-methodology-and-definitions)) These are not universal execution rules: ASX also operates auctions and Centre Point midpoint matching, as explained in its Reporting misconduct FAQs listed in Sources. Screen prices therefore need to be read alongside the trading mechanism and available quantity.

The spread measures a gap, not a forecast

The quoted bid–ask spread is the difference between the best ask and best bid. ASIC’s methodology expresses that gap relative to the prevailing midpoint before averaging observations. That denominator matters: dividing by the bid or last price produces a different percentage. ([asic.gov.au](https://www.asic.gov.au/regulatory-resources/markets/market-structure/equity-market-data/quarterly-cash-equity-market-data-release-methodology-and-definitions)) Fictional example, with all amounts in Australian dollars: a share has a best bid of A$0.48 and best ask of A$0.52. Its spread is A$0.04 and midpoint is A$0.50. The midpoint-based spread is A$0.04 ÷ A$0.50 × 100 = 8%. If someone hypothetically bought 1,000 shares at A$0.52 and immediately sold them at A$0.48, with sufficient quantity and unchanged quotes, the difference would be A$40 before fees. That calculation illustrates crossing the spread under fixed assumptions, not a predicted loss or future price movement.

Quantity changes the meaning of a price

ASX distinguishes Level 1 best bid and offer information from Level 2 full-depth order-book information. A top-of-book quote shows the best prices, not every displayed price level. ([asx.com.au](https://www.asx.com.au/connectivity-and-data/information-services/price-data/real-time-data)) ASIC separately measures depth because the amount available matters as well as the price gap (see the Depth subsection of ASIC: Market data methodology and definitions, listed in Sources). Extend the fictional example: the last trade was A$0.50, but sellers now display 2,000 shares at A$0.52 and another 3,000 at A$0.54. Assume a 5,000-share purchase can execute against both levels, with no cancellations, competing orders, other liquidity or fees. Its cost would be (2,000 × A$0.52) + (3,000 × A$0.54) = A$2,660, averaging A$0.532 a share. Neither the A$0.50 last price nor the A$0.52 best ask describes the whole purchase. This simplified book is a snapshot, not a promise. ASX describes order queues changing as orders are entered, amended or cancelled, including while an order travels through a broker’s systems to the exchange. ([asx.com.au](https://www.asx.com.au/about/contact-asx/report-misconduct/reporting-misconduct-to-asx-faqs))

A stale trade is not the same as a delayed feed

Two clocks matter: when the transaction occurred and when the information reached the screen. ASX supplies post-trade data separately from order-book information. The practical implication is that a current feed does not necessarily mean the last transaction was recent. ([asx.com.au](https://www.asx.com.au/connectivity-and-data/information-services/price-data/real-time-data)) Separately, ASX’s Reporting misconduct FAQs identify a 20-minute delay for its website market data (see the ASX: Reporting misconduct FAQs reference in Sources). That statement is not a description of every broker’s feed. A useful reading checklist is the last-trade timestamp, quote timestamp, stated delay, exchange or venue coverage, and instrument status. This follows from the distinction between trade records, order-book updates and a changing queue: a screenshot alone cannot guarantee that a displayed price remains executable. ([asx.com.au](https://www.asx.com.au/connectivity-and-data/information-services/price-data/real-time-data)) Trading phase also matters. ASX explains that before its opening and closing auctions, orders can queue without matching. An apparent overlap between bids and offers at those times therefore need not represent an immediately available continuous-market trade. ([asx.com.au](https://www.asx.com.au/about/contact-asx/report-misconduct/reporting-misconduct-to-asx-faqs))

A price limit answers only one part of the problem

A buy limit sets the maximum execution price; a sell limit sets the minimum. The SEC’s Trading Basics bulletin explains that execution must be at the limit or better, but is not guaranteed. These are general order definitions, not a claim that every broker offers identical order types or instructions. ([sec.gov](https://www.sec.gov/tm/investor-alerts-bulletins/trading101basics.pdf)) In the fictional book, a 5,000-share purchase limited to A$0.52 could take the 2,000 shares at that price, assuming partial execution is permitted and the displayed shares remain available. It could not take the A$0.54 offers. The price condition does not create the missing 3,000 shares at an acceptable price. The practical distinction is between transaction history, displayed trading interest and executable quantity. Reading them together explains why a single quoted number is not a guaranteed execution price for every order size. ([sec.gov](https://www.sec.gov/tm/investor-alerts-bulletins/trading101basics.pdf))

Go to the source

ASX: Real-time market data, undated; checked 24 October 2026ASIC: Market data methodology and definitions, reissued July 2020; checked 24 October 2026ASX: Reporting misconduct FAQs, undated; checked 24 October 2026SEC: Trading Basics investor bulletin, March 2011, page 1; checked 24 October 2026

AI-assisted reporting. Beyond ASX, its publisher and relevant contributors receive no payment, shares, options, sponsorship or other benefits for this coverage. They hold no securities in the companies covered and have no commercial relationships with them. This coverage involves no paid broker referrals or other referral income.

Spotted something we should correct?

Request a correction