MIAX Updates Round Lot Definition to Sync with Regs
Published Date: 9/2/2025
Notice
Summary
MIAX PEARL 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 MIAX PEARL and kicks in right away, with no extra costs involved. It also tweaks some related rules to keep everything neat and clear.
Analyzed Economic Effects
2 provisions identified: 2 benefits, 0 costs, 0 mixed.
Round Lot Sizes Align with Reg NMS
If you trade equities on MIAX Pearl, the Exchange will adopt the Regulation NMS definition of a “Round Lot” starting November 3, 2025. Under that rule, a Round Lot is 100 shares for stocks with an average closing price of $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; round lot sizes are reassigned semiannually using a one‑month Evaluation Period (March for May assignments; September for November assignments).
Rulebook Edits Improve Clarity for Members
MIAX Pearl will make non‑substantive edits to several rules effective November 3, 2025, such as capitalizing the term “Round Lot,” dividing and renumbering paragraph (b) of Rule 2616, and replacing the term “System Security” with “NMS Security.” The Exchange says these edits are intended only to improve clarity for Equity Members and the public and do not change how the rules operate or impose costs.
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