Fill Or Kill Order (FOK)

Intermediate

Key Takeaways

A Fill or Kill (FOK) order instructs an exchange to execute an order in full immediately or cancel it entirely. No partial fills are allowed.
FOK orders are commonly used by traders who need a specific quantity filled instantly, such as in arbitrage strategies or large block trades across multiple venues.
FOK differs from Immediate or Cancel (IOC) orders, which allow partial fills, and from All or Nothing (AON) orders, which require full execution but without an immediate time constraint.
FOK orders depend on available liquidity. In illiquid markets, FOK orders are frequently rejected because the full quantity cannot be matched at the moment of submission.

What Is a Fill or Kill (FOK) Order?

A Fill or Kill (FOK) order is a conditional order type that instructs an exchange or trading platform to execute the entire order immediately at the specified price or better, or to cancel it entirely. If the order book does not contain sufficient volume to fill the order in full at the moment of submission, the order is killed (canceled) instantly. No partial execution is permitted.

FOK orders are typically placed as limit orders, meaning the trader also specifies a maximum buy price or minimum sell price. The exchange's matching engine checks whether the full quantity is available at that price or better. If yes, the order fills completely. If not, it is canceled without any execution.

How Does a Fill or Kill Order Work?

When a FOK order is submitted, the following sequence occurs:

The order is sent to the exchange with a specified quantity, price, and the FOK time-in-force condition.
The matching engine scans the order book for enough available volume to fill the order in full at the specified price or better.
If sufficient volume exists, the order executes completely in a single transaction.
If insufficient volume exists, the order is immediately canceled. No portion of the order is filled.

This process happens in milliseconds on modern electronic exchanges. FOK orders are supported on most major derivatives and spot trading platforms, including Binance Futures, CME Group Globex, NYSE, and NASDAQ. Availability can vary on basic spot markets with lower trading volumes.

FOK vs. IOC vs. AON Orders

FOK is one of several conditional order types designed to give traders control over how and when their orders execute. The key distinctions are:

Fill or Kill (FOK): Must execute in full immediately, or be canceled entirely. No partial fills. Time constraint is immediate.
Immediate or Cancel (IOC): Executes as much as possible immediately. Any unfilled portion is canceled. Partial fills are allowed.
All or Nothing (AON): Must execute in full like FOK, but is not restricted to an immediate time window. An AON order can remain open until it can be fully filled or the trader cancels it.

The key distinction between FOK and AON is timing. FOK combines the "all or nothing" requirement with an "immediate" time constraint. AON preserves the completeness requirement but removes the urgency. FOK and IOC both prioritize speed, while AON prioritizes completeness over immediacy. Market orders, by contrast, execute at whatever price is available and typically allow partial fills.

When Are Fill or Kill Orders Used?

FOK orders are commonly used in situations where:

A trader needs to establish a specific position size and cannot accept a smaller partial fill. For example, a trader executing a cross-venue arbitrage strategy may need to buy exactly 500 units of a token on one exchange while simultaneously selling 500 on another. A partial fill on one leg would expose them to unintended risk.
Speed and certainty matter more than getting a fill at all. If a price opportunity exists only briefly, a FOK order lets the trader attempt to capture it without leaving a resting order in the book that could execute at a worse time.
The trader wants to probe liquidity across multiple venues simultaneously. By placing FOK orders on several exchanges at once, a trader can wait for one to fill completely and then cancel the remaining orders, avoiding the risk of being filled on all of them at the same time.

FOK orders are less suited to illiquid markets or low-volume trading pairs, where the likelihood of a full immediate fill is low and orders may be rejected repeatedly.

FAQ

What does "fill or kill" mean in trading?

"Fill or kill" means an order must be completely filled at the specified price (or better) the instant it is submitted, or it is canceled entirely. There is no middle ground: either the full quantity executes immediately, or nothing executes at all.

What is the difference between FOK and IOC?

A Fill or Kill (FOK) order requires full execution immediately or it is canceled entirely. An Immediate or Cancel (IOC) order also requires immediate execution but allows partial fills: whatever quantity is available right now will execute, and the remainder is canceled. FOK is stricter because it rejects partial outcomes.

When should I use a fill or kill order?

FOK orders are most useful when you need a precise quantity filled without any risk of a partial position. Common scenarios include cross-venue arbitrage, institutional block trades, and situations where a partial fill would leave you with an unintended or unhedged exposure. They are less effective in thin or illiquid markets, where full immediate fills are uncommon.

Do all crypto exchanges support FOK orders?

Not all exchanges support FOK orders. Major derivatives platforms such as Binance Futures and CME Group Globex support FOK natively. Some basic spot markets and smaller exchanges may not offer FOK as an order type. It is worth checking your platform's order types documentation before relying on FOK in a strategy.

Closing Thoughts

FOK orders are useful when execution certainty matters more than simply getting some of the order filled. By requiring the full quantity to execute immediately or not at all, FOK orders can help traders avoid unwanted partial positions, especially in arbitrage, hedging, or large-size trading strategies. However, their strict conditions also mean they depend heavily on available liquidity and may be canceled frequently in thinner markets. As with any order type, traders should understand how FOK works on their chosen platform before using it in live trading.