Why Your Price Can Differ From the Trader's

Your copy is placed seconds after the trader's fill, and the market has often moved in between. That is the short answer. The trader got their price first, their own order used up liquidity at that price, and by the time your order reaches the book the next available price can be a step worse. Polycopy caps how far that step can go with your slippage tolerance, and skips the trade rather than chase beyond it.

Copying is reactive by nature. Polycopy sees the trader's fill, builds your order, and sends it to Polymarket. That takes seconds, and in an active market seconds are enough for the price to change. Sometimes it moves in your favor. More often the same news that prompted the trade attracts other buyers too, and the price ticks up before your order arrives.

A price on Polymarket is not a quote for unlimited size. The order book holds a certain number of shares at each price level. Once the shares at 50¢ are gone, the next buyer pays 51¢ or 52¢. Your copy can fill at the next level up simply because the level the trader hit no longer exists.

This is the part that surprises people. The trade you are copying is itself a reason the price moved. The trader's buy consumed the cheap shares on the book, and you cannot buy liquidity that someone else already took. The someone else here is the person you are copying. The bigger their trade relative to the market, the further the price steps away before your copy lands.

Your slippage tolerance (default 7%, adjustable down to 2%) sets the worst price your order will accept relative to the trader's. Inside that tolerance, the order fills at whatever the book offers. Beyond it, the copy is skipped instead of filled at a much worse price. A skipped copy can feel like a failure, but it is the protection working. The alternative was owning the same position at a price that may no longer have made sense.