Fill or Kill (FOK)

Written By:
Paul Tracy
Updated October 7, 2020

What is Fill or Kill (FOK)?

Fill or kill (FOK) is a client's instruction to his or her broker to either fill the entire order immediately or to cancel the order.

How Does Fill or Kill (FOK) Work?

Let's assume you want to purchase 1 million shares of Company XYZ at $20 per share. You might instruct your broker to "fill it or kill it," meaning that your broker should buy the entire one million shares at $20 a share within a few seconds or do nothing at all. 

Why Does Fill or Kill (FOK) Matter?

When traders are aware of a big order, they will drive the price up, thinking that the big buyer will be willing to pay more. Fill or kill orders are useful in these circumstances because the investor can attempt to lock in a certain price.