Stock Exchange Quietly Changes Post-Only Order Rules – Traders Shrug
Published Date: 12/19/2025
Notice
Summary
Investors Exchange LLC (IEX) is changing how it handles Post Only orders that might lock or cross prices from other markets. This update helps make trading smoother and fairer for investors using IEX, starting right away with no extra fees. Traders and market participants should watch for these changes to keep their orders working just right.
Analyzed Economic Effects
3 provisions identified: 3 benefits, 0 costs, 0 mixed.
Post Only Orders Re‑priced One MPV
If your firm sends a Post Only order to IEX that would lock or cross a Protected Quotation on another market, IEX will re-price that order before booking it so it rests one (1) minimum price variant (MPV) below the current NBO for bids or one (1) MPV above the current NBB for offers (for example, a buy limit at $10.20 would rest at $10.19).
Rule Change Aims to Encourage Displayed Liquidity
IEX says this change aligns Post Only handling with Nasdaq and NYSE, and is intended to encourage Members to submit more Post Only orders and post more displayed liquidity on IEX; IEX states that increased displayed liquidity should benefit all market participants, including liquidity takers.
Post Only Orders May Still Execute Against Trade Now
A Post Only order will still execute immediately as a liquidity‑adding order if it locks a resting non‑displayed order that has a Trade Now instruction, provided the Post Only order does not also lock a Protected Quotation of an external market.
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