Cboe BZX Aligns Trading Definitions with New Round Lot Rules
Published Date: 11/20/2025
Notice
Summary
Cboe BZX 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 and brokers using the exchange and takes effect immediately, with no extra costs involved. It’s all about keeping things clear and consistent so trading runs smoothly!
Analyzed Economic Effects
2 provisions identified: 2 benefits, 0 costs, 0 mixed.
Round Lot Becomes Price-Based
If you trade on Cboe BZX, the definition of a 'round lot' will change from a fixed 100 shares to a price-based size effective November 3, 2025. Under Rule 600 of Regulation NMS a round lot will be: 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 assignment is recalculated semiannually using a one-month Evaluation Period (March for May assignments; September for November assignments).
Rulebook Language Updated for Clarity
Cboe BZX will update related Exchange rules to remove fixed share references and instead reference the new round lot definition on November 3, 2025. For example, phrases like 'one hundred (100) shares' and the reference to 'five round lots' usually being '500 shares' will be replaced so 'normal unit of trading' means the round lot defined in Exchange Rule 11.10. The change is intended to reduce confusion for Exchange Members and the public.
Your PRIA Score
Personalized for You
How does this regulation affect your finances?
Sign up for a PRIA Policy Scan to see your personalized alignment score for this federal register document and every other regulation we track. We analyze your financial profile against policy provisions to show you exactly what matters to your wallet.
Key Dates
Department and Agencies
Take It Personal
Get Your Personalized Policy View
Start a Free Government Policy Watch to see how policy affects your household, then upgrade to PRIA Full Coverage for year-round monitoring.
Already have an account? Sign in