Fill-or-kill order

A fill-or-kill order must execute immediately and in its entirety, or it is canceled right away. There is no partial fill option and no waiting period, the broker either finds enough matching volume to fill the whole order the instant it hits the market, or the entire order is withdrawn. This makes it one of the stricter order conditions available, combining the full-size requirement of an all-or-none order with the immediacy of an immediate-or-cancel order.

This kind of order suits situations where a trader needs certainty about getting the full position at a specific moment and would rather have no trade at all than an incomplete one that leaves them with an unintended partial position. It is more common in options and futures trading, and in larger block trades, than in ordinary retail stock trading, since a typical retail order in a liquid large-cap stock rarely has trouble filling completely anyway.

Because a fill-or-kill order demands both full size and instant execution, it is the hardest condition to satisfy and often will not fill at all in less liquid securities, even if the trader would have been willing to wait. Traders who want the all-or-none guarantee without the instant timing pressure typically use a plain all-or-none order instead, which can remain open and wait for the right volume to appear rather than canceling immediately.