Partial Fill
A partial fill happens when only part of your order executes immediately. The rest may wait, cancel, or fill later at different prices.
Definition
A partial fill occurs when only a portion of your order executes right away. The remaining quantity stays open, may fill later, or may be cancelled.
Why it matters
Partial fills often happen in thin markets or when you trade size relative to market depth. They increase the chance of multiple execution prices, which changes your execution price and therefore your measured costs.
Common pitfalls
Assuming the rest will fill at the same price: The market can move while the remainder is waiting.
Ignoring time risk: Waiting exposes you to adverse selection and quote changes.