what does fill or kill mean in stocks? FOK
Fill-or-Kill (FOK) order
Quick answer: The question "what does fill or kill mean in stocks" refers to a Fill-or-Kill (FOK) order — a time-in-force instruction that requires an order to be executed immediately and entirely or canceled. This guide explains the definition, mechanics, variants, example scenarios, exchange differences, risks, best practices, and how to place an FOK on trading platforms (including Bitget).
Definition
An FOK (Fill-or-Kill) order is a time-in-force order type used in securities trading that demands immediate and complete execution or automatic cancellation. In plain terms, an FOK instructs the exchange or broker that the requested quantity must be filled in full right away at the specified price (or better). If the full quantity cannot be matched instantly, the order is killed (canceled) with no partial execution.
The phrase "what does fill or kill mean in stocks" directly points to this all-or-nothing, immediate-execution characteristic, which distinguishes FOK from other order types that permit partial fills or extended time windows.
Key characteristics
- Time-in-force: immediate. An FOK is evaluated at submission and must be filled immediately or cancelled.
- All-or-none requirement: no partial fills under the classical definition — the entire quantity must be available at the acceptable price.
- Typical pairing: can be used with limit orders or market orders, though most practical uses are limit-based to control price.
- Use cases: frequently used for large/block trades, time-sensitive strategies, and algorithmic orders that must avoid partial fills.
- Execution certainty vs. fill probability tradeoff: you either get the full execution immediately or nothing.
How an FOK order works
When a trader sends an FOK order, the broker or exchange immediately attempts to match the entire requested quantity at the stated limit price (or better). The typical sequence:
- Order submission: the trader specifies quantity, side (buy/sell), price (limit or market), and time-in-force = FOK.
- Matching attempt: the exchange routing system checks current resting orders and available liquidity across designated venues (subject to broker routing rules and exchange policies).
- Immediate outcome:
- If enough contra-side liquidity exists to satisfy the entire quantity at the specified price (or better), the order is executed in full.
- If not, the order is canceled (killed) with zero fills.
- Notification: the trader receives an execution report indicating a full fill or a cancellation.
This immediate exposure to market liquidity and the all-or-nothing requirement are the defining operational features traders rely on when they ask "what does fill or kill mean in stocks?"
Immediate-execution requirement
The "immediate" part means the exchange evaluates the order upon arrival. In practice, the matching window is extremely short — often measured in milliseconds or a few seconds depending on the venue. Exchanges and smart-routings will examine available contra-side orders at the requested price points. If the total available quantity meets or exceeds the requested size within that instant, the fill occurs.
Because of the time constraints, network latency, order queue position, and routing policies can influence whether an FOK succeeds. For large quantities or thinly traded instruments, the chance of immediate full execution declines.
All-or-none requirement
The "all-or-none" part means partial fills are not acceptable under the classical FOK definition. If only part of the quantity can be matched immediately, the entire order is canceled. This prevents executing a small portion of a large intended trade, which could leave the trader with an undesired residual and altered market exposure.
Some venues offer hybrid behaviors or different interpretations; see the exchange and routing differences section below for details and exceptions.
Variants and related order types
Understanding related order types helps place FOK in context and answers related queries about "what does fill or kill mean in stocks" compared with alternatives.
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Immediate-or-Cancel (IOC): An IOC attempts immediate execution but will accept partial fills. Any unfilled portion is canceled immediately. IOC is useful when you want any liquidity available now, even if it is less than your requested size.
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All-or-None (AON): AON requires full execution like FOK, but an AON order may remain open until the full quantity becomes available (depending on the chosen time-in-force). AON lacks the strict immediate-cancellation requirement; it focuses on full fill but not necessarily instant fill.
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Fill-and-Kill / Fill-and-Accept: Less-standard terms sometimes used by venues; these may allow some partial fill and then cancel the remainder immediately or after a brief interval. Terminology and behavior vary across exchanges.
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Iceberg orders: Not a direct substitute, but iceberg orders hide the full size and display only a portion to the market. They help execute large orders over time without revealing full intent, different from FOK's immediate-all-or-none logic.
When traders ask "what does fill or kill mean in stocks?" they often want to know whether an FOK or IOC better suits their goals — FOK for strict full execution now, IOC for capturing any available liquidity immediately.
Exchange and routing differences
Exchanges and broker-dealers can implement and interpret FOK differently. Key variations include:
- Strict FOK: Some venues enforce a rigid rule — if the entire quantity at the requested price (or better) isn’t available immediately, the order is canceled with zero fills.
- Hybrid implementations: Other venues may treat FOK like an IOC at certain matching points or as an AON with immediate evaluation at the primary book then routing to other destinations. Some systems may allow a partial fill from the first best bid/offer and cancel the remainder; this differs from classical FOK.
- Routing policies and smart order routers: Brokers' routing logic can affect behavior. For example, a broker might check multiple venues for instant liquidity and aggregate available size; some may not route to all venues under certain conditions.
- Interlisted securities and multiple order books: For stocks traded on multiple venues, achieving an immediate full fill may require checking across those books. Routing delay and venue-specific rules affect success probability.
Because of this variability, traders should confirm with their broker or the specific exchange whether their FOK will behave strictly (no partial fills) or with hybrid allowances. When using crypto or alternative trading systems, platform documentation should be reviewed because order-type semantics are not universally standardized.
Practical examples
Example 1 — Successful FOK fill (buyer):
- A trader submits a buy FOK limit order for 100,000 shares at $10.00.
- The exchange’s matching engine finds resting sell orders totaling 100,000 shares at $10.00 or better.
- The trade executes immediately and completely for 100,000 shares at the specified price(s).
- The trader receives a full-fill execution report.
Example 2 — FOK killed (insufficient liquidity):
- A trader submits a sell FOK limit order for 200,000 shares at $5.50.
- At submission, the exchange finds only 150,000 shares available at $5.50 or better.
- Because the full 200,000 shares cannot be matched instantly, the FOK order is canceled and no execution occurs.
- The trader receives a canceled (killed) execution report.
Example 3 — IOC alternative behavior for comparison:
- If the trader had used IOC for the 200,000-share sell order and 150,000 shares were available, the IOC would execute the 150,000 immediately and cancel the remaining 50,000.
These illustrations show the core difference: under FOK you either obtain complete execution right away or nothing — which is the practical meaning behind "what does fill or kill mean in stocks."
Typical use cases
Who uses FOK orders and why:
- Institutional traders handling block trades: They may need to ensure a large block is filled en bloc to avoid leaving a partial position.
- Algorithmic strategies that require deterministic outcomes: Some algorithms must know whether a full execution happened instantly to move to the next step.
- Time-sensitive traders: If execution must occur instantly (for example, to secure a price for a subsequent paired transaction), FOK removes the uncertainty of partial fills over time.
- Risk managers: Avoid partial fills that could alter hedging ratios or risk exposures.
Retail traders rarely need FOK unless executing particularly large or conditional trades. When using large quantity orders, traders often coordinate with broker-dealers' block desks to handle execution and routing.
Advantages and disadvantages
Advantages
- Certainty of outcome: Either you receive the full execution immediately or you don't trade at all.
- Control of execution risk: Avoids partial fills that could leave an unwanted residual position.
- Reduced market-impact risk in some workflows: By avoiding partial hits and subsequent re-entry, you may limit price slippage from repeated executions.
Disadvantages
- Higher probability of non-execution: If sufficient liquidity isn’t present at the requested price immediately, the order will be canceled.
- Missed opportunities: An FOK may be canceled even if liquidity would have become available a few seconds later.
- Exchange variance: In fragmented markets, differing interpretations of FOK reduce predictability.
Risks, limitations and best practices
Risks and limitations
- Order frequently killed: For large or illiquid instruments, FOKs are often canceled, which can disrupt intended strategies.
- Hidden liquidity and dark pools: Some liquidity may be non-displayed. An FOK that checks only displayed size might be killed even though non-displayed liquidity could have filled it.
- Slippage if repriced: Using a market-type FOK in volatile conditions can lead to undesirable fills if not properly constrained by limits.
- Exchange-specific quirks: Some venues may effectively treat FOK as hybrid IOC/AON; assuming uniform behavior is risky.
Best practices
- Talk to your broker desk: For large orders, coordinate with the broker’s trading desk to understand routing, aggregation, and potential block execution services.
- Choose the right order type: If you can accept partial fills, IOC may improve fill probability. If you can wait, AON or GTC with an appropriate limit may be better.
- Test in small sizes: Verify how the platform implements FOK with low-stakes orders before sending large quantities.
- Monitor venue documentation: Exchanges and platforms post their order-type semantics; confirm whether their FOK is strict or hybrid.
- Consider iceberg or algorithmic execution: When you want to minimize market impact while executing large size, specialized algos can help spread execution over time.
Regulatory and broker considerations
Regulators and investor-education resources explain order types and risks. Traders should consult official guidance and broker policy statements to confirm behavior and disclosure.
As of 2026-01-15, according to Investor.gov (the U.S. Securities and Exchange Commission’s investor education site), Fill-Or-Kill orders require immediate and full execution or cancellation and traders should understand how their broker and exchange implement these instructions. Broker-dealers may display their order routing policies and order-type implementations in client agreements or regulatory filings; traders should review these documents to avoid surprises.
Broker-dealer lists and exchange rulebooks may place limitations on the use of FOK for retail accounts or for particular securities; some brokers discourage or don’t support FOK due to complexity.
FOK and other markets (including cryptocurrency)
The concept behind FOK exists in other markets beyond equities, such as options, futures, and cryptocurrency spot trading. However, implementation varies:
- Traditional exchanges (stocks, options, futures): Many have well-defined FOK semantics, though venue-specific differences exist.
- Cryptocurrency exchanges and platforms: Order-type semantics are not universally standardized. Some crypto platforms offer time-in-force equivalents labeled FOK or immediate variants, but behavior can differ (for example, how routing to liquidity pools or matching engines is handled).
When trading on crypto platforms, always verify that the platform’s FOK behaves as expected. If you use Bitget, consult Bitget’s order-type documentation and consider contacting Bitget support or the trading desk to confirm behavior for large or institutional orders. Bitget Wallet is the recommended Web3 wallet for on-chain interactions when bridging between centralized and decentralized environments within the Bitget ecosystem.
How to place an FOK order
General steps (these may vary slightly by broker or platform):
- Choose the instrument and side (buy or sell).
- Specify quantity and price (limit orders are common with FOK to control execution price). Avoid market FOK unless you accept the potential price range in volatile markets.
- Select time-in-force = Fill-or-Kill (FOK) from the platform’s order-type menu.
- Review routing and execution options: some platforms allow you to choose routing preferences or to enable smart routing.
- Submit the order. Expect an immediate execution report showing full fill or cancellation.
- If executing a large order, coordinate with a trade desk or use algorithmic execution tools available on the platform.
On Bitget:
- Use the Bitget trading interface and set the time-in-force parameter to FOK when the option is available.
- For large sizes, contact Bitget’s institutional or OTC desk to discuss block execution and confirm whether Bitget’s routing will aggregate liquidity across internal and external pools.
- If you hold assets in Bitget Wallet and plan to move between on-chain and exchange liquidity, confirm the sequence and possible delays.
See also
- Immediate-or-Cancel (IOC)
- All-or-None (AON)
- Good-'Til-Canceled (GTC)
- Limit order
- Market order
- Iceberg order
References
- Investor.gov (U.S. SEC) — Fill-Or-Kill Order (investor-education resource explaining FOK semantics). Reported as of 2026-01-15.
- Investopedia — Fill or Kill (FOK) Order Explained. Reported as of 2026-01-15.
- Corporate Finance Institute (CFI) — Fill or Kill (FOK) definition and examples. Reported as of 2026-01-15.
- Nasdaq glossary — Fill or Kill order (FOK) definition. Reported as of 2026-01-15.
- Wikipedia — Fill or kill (overview of market order types). Reported as of 2026-01-15.
- Deutsche Börse glossary — Fill or kill explanation. Reported as of 2026-01-15.
Further reading: consult your broker’s order-type documentation and the exchange rulebook for venue-specific behaviors.
Practical checklist before using FOK
- Confirm platform FOK semantics (strict FOK vs. hybrid)
- Determine whether you can accept zero fills if full liquidity isn’t available
- Consider IOC or algorithmic alternatives to improve execution probability
- Contact Bitget support or a trading desk for large orders
- Test behavior with a small trade to verify routing and execution reports
Frequently asked questions (FAQ)
Q: Is FOK the same as IOC? A: No. While both are immediate, IOC allows partial fills and cancels remaining quantity; FOK requires full execution immediately or cancellation.
Q: Can retail traders use FOK? A: Yes, if the trading platform supports FOK. However, for most retail needs IOC or limit/GTC orders are more practical.
Q: Are FOK semantics identical across exchanges? A: No. Exchange and broker implementations vary; always check platform documentation to confirm.
Q: Does an FOK guarantee the best price? A: An FOK will execute only at the specified limit or better. It does not guarantee the absolute best price across non-displayed liquidity or venues the broker may not access.
Further exploration and next steps
If you are preparing to execute sizable or time-sensitive orders, review your platform’s order-type documentation and test behavior with small orders. For professional or institutional needs, coordinate with Bitget’s trading desk to confirm routing, available liquidity aggregation, and whether FOK is the optimal choice for your strategy. Explore Bitget’s advanced order types and Bitget Wallet for holistic trade and custody workflows.
As you continue learning about FOK, remember the core answer to the central question: when someone asks "what does fill or kill mean in stocks" — it means an immediate, all-or-nothing order instruction that either fills entirely on arrival or is canceled.
Interested in practicing order types? Try a demo account or contact Bitget support to understand how FOK behaves on the Bitget platform.
