Partial Fill
When only part of an order's total size executes against available liquidity, leaving the remainder either still open on the order book or canceled, depending on the order's instructions.
A partial fill occurs when only a portion of an order's total requested size is actually executed, typically because the available liquidity at the order's price at that moment isn't sufficient to fill the entire size at once. What happens to the unfilled remainder depends on the order's specific instructions: a standard limit order generally leaves the remainder open on the book to potentially fill later, while an order marked Fill-or-Kill (see Kaavon's "Fill-or-Kill (FOK)" glossary definition) instead cancels the entire order rather than accepting any partial fill at all.
Partial fills are a normal, routine occurrence in markets with limited liquidity at a given price level, and traders executing large orders often plan around the likelihood of partial fills by using execution strategies like TWAP (see Kaavon's "Time-Weighted Average Price (TWAP)" glossary definition) that break a large order into smaller pieces specifically to manage this dynamic, rather than attempting to fill the entire size in one attempt.
Examples
- A large limit order placed in a thinly traded market might receive only a partial fill initially, with the remaining unfilled portion staying open on the order book.
- Unlike a standard order, which leaves an unfilled remainder open, a Fill-or-Kill order specifically rejects any partial fill, canceling the entire order instead.