Glossary term
Fill-or-Kill Order
A fill-or-kill order must be executed immediately and completely, or it is canceled.
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What Is a Fill-or-Kill Order?
A fill-or-kill order, or FOK order, is a trading instruction that must be executed immediately and in full or canceled. It does not allow partial execution, and it does not remain open in the market waiting for later liquidity.
FOK orders are most useful when the trader wants all of a specified quantity at acceptable terms right away. If the market cannot provide the full quantity immediately, the order is killed, meaning canceled.
Key Takeaways
- A fill-or-kill order must fill immediately and completely.
- If the full order cannot execute, the entire order is canceled.
- FOK orders do not allow partial fills.
- They are often used when execution size and immediacy both matter.
- They can reduce partial-fill risk but may increase the chance of no execution.
How a Fill-or-Kill Order Works
A trader enters an order with a quantity, side, and price condition, usually as a limit order. The trading system checks whether the full quantity can be executed immediately at the specified price or better. If yes, the order fills. If not, the order is canceled.
For example, a trader who wants to buy 10,000 shares at no more than $25 may use an FOK limit order. If only 6,000 shares are available at or below $25, the order does not partially fill. It cancels instead.
This instruction can matter when a partial position would be undesirable. A trader may need the full quantity to hedge another exposure, complete an arbitrage, or avoid revealing interest in a thin market.
FOK Compared With Related Order Instructions
Instruction | What it requires | Partial fills? |
|---|---|---|
Fill-or-kill | Immediate full execution or cancellation | No |
Immediate-or-cancel | Immediate execution of any available amount | Yes |
All-or-none | Full execution only, but not always immediate | No |
Day order | Open only for the trading day | Usually yes |
Limits and Misunderstandings
A fill-or-kill order does not guarantee execution. In fact, it can make execution less likely because the market must satisfy the full quantity immediately.
It also does not guarantee a better price than other order types. A limit price can control the worst acceptable price, but liquidity, spread, volatility, and routing still affect whether the order can fill.
FOK orders are specialized. For many ordinary trades, a limit order, market order, or immediate-or-cancel order may be more practical depending on whether price control, speed, or completion matters most.
The Bottom Line
A fill-or-kill order is an all-or-nothing immediate execution instruction. It is useful when a partial fill would create a problem, but it can also result in no trade at all.