IEX Fine-Tunes Math Rule for Smoother Stock Quote Handling
Published Date: 5/11/2026
Notice
Summary
Investors Exchange (IEX) is tweaking a math rule that helps spot unstable stock quotes to make it work better. This change affects traders using IEX by improving how orders are handled, with no extra costs or delays. The update kicks in right away, keeping trading smooth and smart!
Analyzed Economic Effects
4 provisions identified: 4 benefits, 0 costs, 0 mixed.
IEX Quotes Added to CQI Reference
IEX will add its own Protected Quotation to the Signal Best Bid and Signal Best Offer used by the crumbling quote indicator (CQI). This change applies to D-Limit, C-Peg, D-Peg, and P-Peg orders and is intended to make the CQI identify unstable quotes in additional situations.
CQI Coverage and On-Time Metrics Rise
IEX's testing shows the CQI Update would raise volume-weighted coverage from 70.1% to 75.0% and increase accuracy from 67% to 68%. The percent of the day CQI is "on" (volume-weighted) would go from 0.368% to 0.400%, and the percent of the day D-Limit is available at the specified limit price is estimated to change from 99.632% to 99.600%.
Execution Markouts Show Incremental Improvement
IEX compared markouts for January–February 2026 and found improvements with the CQI Update. For standard lit limit orders (trade-to-mid, % of spread) 1 ms markouts improve from 27% to 32%, 10 ms from 22% to 26%, 100 ms from 18% to 21%, and 1000 ms from 12% to 15%. For midpoint peg orders, 1 ms improves from 1.6% to 1.7% and 1000 ms from 1.5% to 1.6%.
May Increase Liquidity and Order Entry on IEX
IEX states the CQI Update may lead to more and larger displayed and non-displayed D-Limit, D-Peg, P-Peg and C-Peg orders being entered on IEX. To the extent more orders are entered, IEX says increased liquidity would benefit IEX members and their customers and improve price discovery.
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