Glossary
Fill or kill (FOK)
An order that must be executed immediately and in full, or cancelled entirely; no partial fills are allowed.
On this page
A fill-or-kill (FOK) order is an instruction to execute the entire quantity at once at the stated price or better, and to cancel it immediately if that is not possible. It combines two conditions: no waiting, and no partial fills. Traders use it when getting only part of a position would be worse than getting nothing, for example when one leg of a planned trade only makes sense at full size.
How it works
The order arrives at the venue and is checked against available liquidity. If enough shares are on offer at acceptable prices, it executes in full; otherwise the whole order is cancelled in the same instant. Nothing rests on the order book.
How it compares with similar instructions
| Instruction | Must be immediate? | Partial fills allowed? |
|---|---|---|
| Fill or kill (FOK) | Yes | No |
| Immediate or cancel (IOC) | Yes | Yes; unfilled rest is cancelled |
| All or none (AON) | No; can wait | No |
| Day order | No; works until the close | Yes |
Where you will see it
FOK is more common in institutional, futures, forex and crypto trading than in retail stock accounts; many US retail brokers do not offer it for equities, or offer only IOC. Because the condition is strict, FOK orders frequently fail in thin markets, so they are a tool for controlling outcome, not for getting filled.