Partial fill
Family II · Orders
Not to be confused with fill or kill order.
Partial fill describes the situation in which an order is executed for less than its full stated size. The unfilled balance is not automatically cancelled; its fate depends on the order's time-in-force instructions and on whether sufficient opposing interest exists at an acceptable price. Partial fills are routine in markets where available liquidity at a given price is smaller than the order.
How a partial fill arises
An order is matched against whatever quantity is available at the best opposing price. If that quantity is smaller than the order, the order is filled only to that extent. The remaining quantity may continue to rest in the order book, be repriced, or be cancelled, according to the order type.
- A limit order typically rests and can receive further partial fills as new interest arrives.
- A market order may be filled across several price levels, producing multiple partial executions that together form one order.
- An immediate-or-cancel instruction cancels any unfilled balance at once.
Worked example
The 600-share balance stays open if the order is a standard limit order, and is cancelled if the order carries an immediate-or-cancel or fill-or-kill instruction.
Consequences and reporting
Each execution against a partially filled order is usually reported separately, so a single order can generate several trade confirmations. Commissions and fees may therefore be charged per execution rather than per order, and the average price of the completed portion can differ from the order's limit price. The treatment of unfilled balances, and the point at which an order is considered complete, vary by venue and by order type.
Often confused with
- fill or kill order
- A fill-or-kill order must be executed in full immediately or cancelled entirely, whereas a partial fill leaves part of the order executed and part unfilled; the visible sign is that a fill-or-kill order produces either one complete execution or none, never a residual open quantity.