{
  "id": "184fb32a-a0c5-51cf-ae2e-f4d8fab06067",
  "slug": "fill-or-kill-order",
  "term": "Fill or Kill Order",
  "aliases": [],
  "category": "Market Microstructure",
  "category_slug": "market-microstructure",
  "difficulty": "basic",
  "definition": "A Fill or Kill (FOK) order is a conditional order instruction requiring that the entire order be executed immediately in full or cancelled entirely, with no partial fills permitted. It is used when a trader requires complete execution at a specific price and cannot accept a fractional fill.",
  "key_takeaways": [
    "An FOK order must be filled in its entirety at the specified price or better, instantaneously upon reaching the market; any inability to fill the complete quantity results in automatic cancellation.",
    "FOK orders are distinct from Immediate or Cancel (IOC) orders, which permit partial fills; FOK is strictly all-or-nothing.",
    "They are commonly used by institutional traders executing large block orders to avoid adverse price impact from partial fills that leave residual exposure.",
    "FOK orders are particularly prevalent in equity, futures, and foreign exchange markets where deep liquidity is required to satisfy the full quantity at a single price level.",
    "The use of FOK orders can signal the urgency and size of institutional demand, and market makers factor the all-or-nothing constraint into their quoting behavior."
  ],
  "detailed_explanation": "A Fill or Kill order represents one of the most restrictive time-in-force conditions available in modern electronic markets. When a trader submits an FOK order, the matching engine at the exchange or electronic communication network (ECN) attempts to match the entire order quantity against available resting liquidity at the specified limit price or better. If sufficient liquidity does not exist to fill the complete order at that moment, the entire order is cancelled without any partial execution taking place. This binary outcome—complete fill or total cancellation—distinguishes FOK from the closely related Immediate or Cancel (IOC) order, which permits partial execution of whatever quantity is immediately available.\n\nThe primary motivation for using FOK orders stems from institutional portfolio management, where executing only a fraction of a desired position can be operationally counterproductive. For example, a hedge fund rebalancing a large equity position may need to acquire exactly 500,000 shares to achieve a targeted portfolio weight; receiving 200,000 shares would expose the fund to unintended factor risk while leaving residual order management obligations. By using an FOK instruction, the fund ensures its position either achieves the intended scale or remains unchanged, preserving portfolio integrity.\n\nFrom a market microstructure perspective, FOK orders interact with the limit order book in a distinct manner. They do not enter the order queue and rest; instead, they are evaluated instantaneously against the current state of the book. This means FOK orders consume liquidity rather than provide it, and their usage can contribute to temporary price pressure when large quantities are demanded simultaneously. Market participants with low-latency infrastructure may detect the arrival of large FOK orders and adjust their quotes accordingly, a dynamic that informs algorithmic trading strategies.\n\nIn fixed income and currency markets, FOK orders serve an especially important function when transacting in bespoke or less liquid instruments. A large pension fund executing a currency hedge through a spot foreign exchange transaction might use an FOK instruction to ensure that the entire hedge notional is placed at a known rate, avoiding the currency mismatch risk that would arise if only a portion of the hedge were executed. Similarly, corporate treasury departments routinely use FOK instructions when executing large currency conversions tied to specific accounting periods.\n\nRegulatory frameworks generally treat FOK orders as standard order types, but their use in certain algorithmic and high-frequency trading contexts has attracted scrutiny. Regulators such as the SEC and ESMA have examined patterns of FOK order submission and cancellation as potential signals of market manipulation, particularly in scenarios where rapid submission and cancellation of large FOK orders could be used to probe available liquidity without genuine trading intent.",
  "example": "A macro hedge fund wishes to establish a long position of 1,000,000 shares of a large-cap technology stock at $150.00 per share. The fund's portfolio manager submits a FOK limit order for 1,000,000 shares at $150.00. At the moment of submission, the exchange's limit order book shows 700,000 shares available at $149.95 and $150.00 combined. Because the full 1,000,000 shares cannot be sourced at $150.00 or better instantaneously, the FOK order is cancelled in its entirety. The fund receives no shares and incurs no market impact. The portfolio manager then reassesses and decides to break the order into smaller tranches using an algorithmic execution strategy, working the order over 30 minutes to minimize market impact.",
  "formula": null,
  "formula_latex": null,
  "interactive_type": null,
  "calculator_id": null,
  "related_terms": [
    "algorithmic-trading",
    "cap",
    "central-counterparty",
    "electronic-communication-network",
    "equity",
    "esma",
    "exchange",
    "good-till-cancelled-order",
    "hedge-fund",
    "high-frequency-trading",
    "latency",
    "limit-order",
    "liquidity",
    "locked-limit",
    "market-impact"
  ],
  "backlinks": [
    "co-location",
    "implementation-shortfall",
    "marking-the-close",
    "settlement",
    "stop-limit-order"
  ],
  "cross_references": [
    "algorithmic-trading",
    "cap",
    "electronic-communication-network",
    "equity",
    "esma",
    "exchange",
    "hedge-fund",
    "high-frequency-trading",
    "latency",
    "limit-order",
    "liquidity",
    "market-impact",
    "market-manipulation",
    "order-book",
    "stock"
  ],
  "tags": [
    "level:basic",
    "cat:market-microstructure"
  ],
  "asset_classes": [],
  "regulators": [],
  "see_also": [],
  "sources": [],
  "wordcount": 750,
  "checksum": "c2751bf546c54cd8",
  "version": "2026.05.03",
  "license": "CC-BY-4.0",
  "updated_at": "2026-09-07T02:15:24+00:00",
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}