Fill or Kill (FOK)
Quick Definition
An order type that must be executed immediately and completely or cancelled entirely—no partial fills allowed.
Key Takeaways
- FOK orders must be filled completely and immediately, or they are cancelled entirely.
- No partial fills are allowed—it's all or nothing in a single instant.
- Used by institutional traders who need exact position sizes, especially in derivatives markets.
What Is Fill or Kill (FOK)?
A fill-or-kill (FOK) order is a time-in-force instruction that requires the entire order to be executed immediately at the specified price (or better), or the order is cancelled in its entirety. Unlike a regular limit order that can sit on the order book and be partially filled, a FOK order demands "all or nothing, right now." This order type is used by institutional traders who need a specific block size for their strategy and cannot accept partial execution. For example, a trader might need exactly 10,000 shares to hedge a derivative position—getting only 6,000 would leave them partially exposed. FOK orders are common in options and futures markets where exact position sizing matters. The related "all-or-none" (AON) order also requires complete execution but doesn't demand immediacy—it can remain active until filled in full or cancelled.
Fill or Kill (FOK) Example
- 1A trader places a FOK order to buy 5,000 shares at $50.00. If only 3,000 are available at that price, the entire order is cancelled.
- 2An options trader uses a FOK order to buy 100 contracts at $2.15—either all 100 fill instantly or the order dies.
Related Terms
All-or-None Order (AON)
A trading instruction that requires the entire order to be filled completely or not executed at all, preventing partial fills.
Limit Order
An order to buy or sell a security at a specific price or better, giving you price control but no execution guarantee.
Market Order
An order to buy or sell a security immediately at the best available current price.
Block Trade
A privately negotiated, large-volume securities transaction that is executed outside the open market to minimize price impact.
Stock
A security representing ownership in a corporation, entitling the holder to a share of profits and voting rights.
Initial Public Offering (IPO)
The first sale of a company's stock to the public, transitioning it from private to publicly traded.
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