Cboe EDGA Updates Round Lot Rules: Trading Norms Get Tweaked
Published Date: 11/21/2025
Notice
Summary
Cboe EDGA Exchange is updating its rules to match a new official definition of a 'round lot'—basically, the standard number of shares in a trade. This change affects traders and brokers using the EDGA platform and kicks in right away with no extra costs. It also tweaks some related rules to keep everything smooth and clear.
Analyzed Economic Effects
3 provisions identified: 3 benefits, 0 costs, 0 mixed.
Round Lot Definition Follows Rule 600
If you trade or clear trades on Cboe EDGA, the Exchange will use the round lot sizes assigned by the primary listing market under Rule 600 of Regulation NMS starting November 3, 2025. Rule 600 assigns round lots by price bands: $250.00 or less = 100 shares; $250.01–$1,000.00 = 40 shares; $1,000.01–$10,000.00 = 10 shares; and $10,000.01 or more = 1 share.
Semiannual Reassignment of Round Lots
Round lot sizes for NMS stocks will be recalculated on a semiannual basis using a one-month Evaluation Period. The rule uses March trading days to set round lots effective the first business day in May, and September trading days to set round lots effective the first business day in November.
New NMS Stocks Use 100-Share Round Lot
For any security that becomes an NMS stock during an operative period, the round lot will be 100 shares. This rule applies during the operative periods described in Rule 600 and is part of the EDGA conforming changes effective November 3, 2025.
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