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Fill Or Kill (FOK)

Posted on October 16, 2025 by user

Fill or Kill (FOK)

What it is

A fill or kill (FOK) order is a time-in-force instruction in securities trading that requires an order to be executed immediately and in full, or else it is canceled. It combines the all-or-none (AON) requirement for a complete fill with the immediate execution focus of an immediate-or-cancel (IOC) order.

Key features

  • Must be filled entirely and immediately, or cancelled (killed).
  • Commonly used for large orders that could move the market if partially filled or executed slowly.
  • Can be placed as a market or limit order depending on the trader’s price constraints.
  • Not frequently used for small retail trades; more typical for active traders or institutional flows.

How it works

  • When submitted, the order is exposed to the market for immediate execution.
  • If the full quantity at the specified price (or better) is available right away, the order is filled.
  • If the full quantity is not immediately available, the entire order is canceled.
  • Some venues may fill the portion available at the first bid/offer and cancel the remainder; practices can vary by exchange.

Example

An investor places a limit FOK order to buy 1,000,000 shares of XYZ at $15.00:
* If 1,000,000 shares are offered at $15.00 (or better) immediately, the order is filled.
If only 700,000 shares are available at $15.00, the entire order is canceled.
If 1,000,000 shares are available but only at $15.01, the order is canceled because it does not meet the price limit.

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When traders use FOK

  • Large block trades where partial execution could adversely affect strategy or create execution risk.
  • Situations where a trader requires certainty about receiving the full position immediately or not trading at all.

Advantages and disadvantages

Advantages:
* Eliminates partial fills that might complicate execution or risk management.
* Reduces the chance that a large order will move the market through staggered fills.

Disadvantages:
* Higher chance the order will not execute at all compared with less restrictive time-in-force options.
* May miss gradual liquidity that could have been captured with other order types (IOC, GTC).

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How FOK differs from similar orders

  • AON (All-or-None): AON requires a complete fill but does not necessarily require immediate execution.
  • IOC (Immediate-or-Cancel): IOC fills whatever quantity is available immediately and cancels the remainder; FOK cancels the entire order if it cannot be filled in full immediately.
  • GTC (Good‑Til‑Canceled): GTC stays open until filled or canceled by the trader, without the immediacy requirement.

Takeaways

FOK orders provide a strict, immediate all-or-nothing execution option designed to handle large trades without partial fills. They offer certainty about execution conditions but increase the likelihood that the trade will not occur. Choose FOK when immediate, complete execution is essential and missing the trade is an acceptable outcome.

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