Cboe BYX Updates Round Lot Rules to Match NMS Standards
Published Date: 11/20/2025
Notice
Summary
Cboe BYX Exchange is updating its trading rules to match a new official definition of a 'round lot'—basically, the standard number of shares in a trade. This change affects traders using the BYX Exchange and kicks in right away, with no extra costs involved. It’s a smooth move to keep things clear and consistent for everyone trading stocks.
Analyzed Economic Effects
2 provisions identified: 2 benefits, 0 costs, 0 mixed.
Round Lot Now Based on Share-Price Tiers
If you trade on the Cboe BYX Exchange, a “round lot” will be the size assigned by the stock's primary listing market under Rule 600 of Regulation NMS: 100 shares for stocks with average closing price $250.00 or less; 40 shares for $250.01–$1,000.00; 10 shares for $1,000.01–$10,000.00; and 1 share for $10,000.01 or more. The round lot for each NMS stock will be reassigned semiannually using a one-month Evaluation Period (March for May assignments; September for November assignments).
Implementation Timing and Immediate Filing
The Exchange filed the change as immediately effective and will implement the amended Rule 11.10 and the conforming edit to Rule 11.8(d)(1) on November 3, 2025, the same date the revised Regulation NMS round lot definition becomes operative. The Exchange states the amendments do not change the operation of the affected rules and are intended to reduce participant confusion.
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