IEX Tweaks Trading Units: Conforming to Federal Share Sizes
Published Date: 11/21/2025
Notice
Summary
Investors Exchange (IEX) is updating its trading rules to match a new national standard for what counts as a 'round lot'—basically, the usual size of a stock trade. This change affects traders using IEX and kicks in right away, making sure everyone’s on the same page without shaking up prices or costs. It’s a smooth move to keep trading simple and fair!
Analyzed Economic Effects
3 provisions identified: 3 benefits, 0 costs, 0 mixed.
IEX adopts new round lot rule
IEX is changing its Rule 11.180 so that the meaning of a "round lot" on the Exchange matches Rule 600 of Regulation NMS. This change is effective November 3, 2025 and applies to trading on IEX so that the Exchange's rule will use the round lot sizes assigned under Rule 600.
New round lot size thresholds
Under the new definition from Rule 600, a round lot for NMS stocks is: 100 shares if the stock's average closing price is $250.00 or less; 40 shares if $250.01–$1,000.00; 10 shares if $1,000.01–$10,000.00; and 1 share if $10,000.01 or more. IEX will use those same share thresholds when determining whether an order is a round lot, odd lot, or mixed lot.
Semiannual reassignments and new listings rule
Round lot assignments are adjusted on a semiannual schedule using one-month Evaluation Periods: March trading days determine round lots assigned the first business day in May, and September trading days determine round lots assigned the first business day in November. Also, any security that becomes an NMS stock during an operative period is treated as having a 100-share round lot.
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