In U.S. equity market structure, an odd lot is an amount smaller than the applicable round lot for the security. Because round-lot size can vary by NMS stock, an odd lot is defined relative to that stock’s applicable round lot; do not reduce the term to “fewer than 100 shares” in every case.
ReviewedEvidence1 sourceSectionPhrases & Idioms
Quick answer
In U.S. equity market structure, an odd lot is an amount smaller than the applicable round lot for the security.
Key details
Canonical Formodd lot
Core MeaningIn U.S. equity market structure, an odd lot is an amount smaller than the applicable round lot for the security.
Further guidance
History Boundary
Current authoritative market-structure meaning is published without claiming an exact inventor, coinage date, or absolute first use.
Meaning
In U.S. equity market structure, an odd lot is an amount smaller than the applicable round lot for the security.
Usage Boundary
Because round-lot size can vary by NMS stock, an odd lot is defined relative to that stock’s applicable round lot; do not reduce the term to “fewer than 100 shares” in every case.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
Odd-Lot Information is a current Regulation NMS defined term. This guide preserves the rule-specific definition and boundaries instead of replacing it with informal market shorthand.
In current U.S. exchange usage aligned to Regulation NMS round lots, a mixed lot is an amount greater than one applicable round lot that is not an integer multiple of that round-lot size. Do not define a mixed lot by a fixed 100-share threshold: the applicable Regulation NMS round lot can vary by security, so the mixed-lot boundary moves with that assigned size.
Under current U.S. Regulation NMS, a round lot for an NMS stock is an assigned unit size that can vary with the stock’s price tier rather than always being 100 shares. Do not use “round lot” as a universal 100-share synonym: the applicable U.S. NMS size can be 100, 40, 10, or 1 share under the price-tier framework, and other markets may use different conventions.
Actionable Indication of Interest is a current federal securities-regulation defined term. This guide preserves the rule-specific definition and boundaries instead of replacing it with informal market shorthand.
Administrative Data is a current Regulation NMS defined term for specified administrative, control, and technical messages in the market-data plan framework.
Affiliate of a Subscriber is a current Regulation ATS defined term. This guide preserves the rule-specific meaning and boundary instead of replacing it with informal market shorthand.
Under current U.S. Regulation NMS definitions, aggregate quotation size is the sum of the quotation sizes of all responsible brokers or dealers communicating bids or offers in an NMS security at the same price. Treat this as a U.S. securities-regulation definition; it should not be generalized to unrelated uses of aggregate size or quotation outside Regulation NMS.
Alternative Trading System is a current federal securities-regulation defined term. This guide preserves the rule-specific definition and boundaries instead of replacing it with informal market shorthand.
