# 2025-22142: MEMX Tweaks Round Lot Rules to Fit New Regs

2025-22142, Self-Regulatory Organizations; MEMX LLC; Notice of Filing and Immediate Effectiveness of a Proposal To Amend Exchange Rule 11.6(q)(1), Round Lot, To Conform With the Amendment to the Definition of Round Lot Under Rule 600 of Regulation NMS Recently Approved by the Commission, is a Federal Register notice from Securities and Exchange Commission published 2025-12-08, effective 2025-11-25 (as of 2026-06-08).

- Canonical: https://policyrisk.com/federal-register/2025-22142
- As of: 2026-06-08
- Plain-text twin of the page above; the HTML and this file carry the same facts.

## Facts
- Document number: 2025-22142
- Title: Self-Regulatory Organizations; MEMX LLC; Notice of Filing and Immediate Effectiveness of a Proposal To Amend Exchange Rule 11.6(q)(1), Round Lot, To Conform With the Amendment to the Definition of Round Lot Under Rule 600 of Regulation NMS Recently Approved by the Commission
- Type: Notice
- Agencies: Securities and Exchange Commission
- Citation: 90 FR 56807
- Published: 2025-12-08
- Effective: 2025-11-25
- Comments close: not stated
- Significant: no
- Touches household money: no
- Regulation identifier numbers: none
- Last updated: 2026-06-08

## In one line

MEMX Tweaks Round Lot Rules to Fit New Regs

## Summary

MEMX is updating its rules to match a new official definition of a 'round lot'—basically, the standard number of shares in a stock trade. This change affects traders and brokers using MEMX and kicks in right away with no extra costs. It also tweaks some related rules to keep everything neat and clear.

## Effects PRIA read

- New official 'Round Lot' sizes: benefit, low. The Exchange updated its definition of a “Round Lot” to match Rule 600(b)(93) of Regulation NMS. Under that definition, a Round Lot is based on a security's average closing price: $250.00 or less = 100 shares; $250.01–$1,000.00 = 40 shares; $1,000.01–$10,000.00 = 10 shares; $10,000.01 or more = 1 s…
- Round lot reassigned twice a year: benefit, low. Round Lot assignments for NMS stocks will be recalculated semiannually based on a one-month Evaluation Period. The March Evaluation Period determines the Round Lot assigned on the first business day of May (operative through the last business day of October), and the September Evaluation Period det…
- MEMX rule change effective immediately: benefit, low. MEMX filed the rule change on November 25, 2025 and the Commission waived the 30-day operative delay, making the conforming changes operative upon filing. The Exchange states the changes are implemented immediately, do not amend the operation of the affected rules, and are intended to reduce invest…

## Related documents

- [2026-20466](https://policyrisk.com/federal-register/2026-20466): Adviser and Regulated Fund Custody Rules; Crypto Custody Rules, 2026-10-06
- [2026-19260](https://policyrisk.com/federal-register/2026-19260): Rescission of Rule 14a-8's Federal Regulation of Shareholder Proposals and Amendments to Rule 14a-4, 2026-09-21
- [2026-18424](https://policyrisk.com/federal-register/2026-18424): Political Contributions by Certain Investment Advisers, 2026-09-10
- [2026-18190](https://policyrisk.com/federal-register/2026-18190): Transfer Agent Rules, 2026-09-04
- [2026-17183](https://policyrisk.com/federal-register/2026-17183): Regulation Crypto Assets, 2026-08-21
- [2026-12163](https://policyrisk.com/federal-register/2026-12163): The Trade-Through Rule and Locked and Crossed Markets Provisions of Regulation NMS, 2026-06-17

## Sources
- [2025-22142 on federalregister.gov](https://www.federalregister.gov/documents/2025/12/08/2025-22142/self-regulatory-organizations-memx-llc-notice-of-filing-and-immediate-effectiveness-of-a-proposal-to)
- [2025-22142 as published (PDF)](https://www.govinfo.gov/content/pkg/FR-2025-12-08/pdf/2025-22142.pdf)

## Related
- [Previous: 2025-22139, Deadline for Submitting Intent To Use Airport Improvement Program (AIP) Apporti…](https://policyrisk.com/federal-register/2025-22139)
- [Next: 2025-22143, Self-Regulatory Organizations; Investors Exchange LLC; Notice of Filing and Imm…](https://policyrisk.com/federal-register/2025-22143)
- [All Federal Register documents](https://policyrisk.com/federal-register)

Source: PRIA, https://policyrisk.com/federal-register/2025-22142 (as of 2026-06-08).