MEMX Tweaks Rules for Post-Only Orders to Prevent Trading Confusion
Published Date: 9/18/2025
Notice
Summary
MEMX is updating its rules to make it clearer how orders with a 'Post Only' instruction are handled, especially when combined with other special instructions. This change affects traders using MEMX and kicks in right away, helping avoid confusion and keep trading smooth. No extra costs are expected, just clearer, faster order processing.
Analyzed Economic Effects
1 provisions identified: 1 benefits, 0 costs, 0 mixed.
Post-Only Orders Can Remove Liquidity
If you trade on MEMX, the Exchange clarified that any order entered with a Post Only instruction may remove displayed liquidity when it is an order to buy or sell a security priced below $1.00 or when removing liquidity would be "economically beneficial" to the firm. The Exchange will determine "economically beneficial" using the highest possible rebate paid and the highest possible fee charged, and this clarification applies whether the order also has a Display-Price Sliding instruction, a Cancel Back instruction, or no additional instruction at all.
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