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A fill or kill (FOK) order is a trade instruction that requires your entire order to be executed immediately and in full, or canceled completely. There is no partial fill option. If the market cannot satisfy the entire quantity at the moment you submit it, the exchange cancels the order and you receive nothing.
Think of a fill or kill order like a restaurant table request for a group of 20: you either seat everyone together right now, or the party walks.
FOK orders are most useful when partial execution creates more problems than no execution at all. Institutional traders assembling large positions in illiquid securities often use FOK to avoid being partially filled at a price that no longer reflects current conditions. If you need exactly 50,000 shares of a thinly traded stock for an index replication trade, receiving 20,000 shares at one price and then having to chase the other 30,000 at a worse price defeats the purpose of the order.
Algorithm-driven trading strategies with strict entry criteria also use FOK to enforce exact execution conditions. If your model says buy this amount at this price right now, a partial fill at a marginally different price can invalidate the strategy's risk parameters.
Immediate or cancel (IOC) and fill or kill sound similar but differ in one important way. An IOC order executes whatever portion of the order can be filled immediately and cancels the rest. A FOK order requires the full amount to be filled immediately or the entire order is canceled. IOC is more forgiving. FOK is absolute.
If you submit an FOK order for 1,000 shares and only 600 shares are available at your price, the entire order is canceled. If you submit an IOC order under the same conditions, you receive 600 shares and the remaining 400 is canceled.
| Order Type | Partial Fill Allowed? | Expiry | Best Use Case |
|---|---|---|---|
| Fill or Kill | No | Immediately | Block trades requiring exact quantities |
| Immediate or Cancel | Yes | Immediately (unfilled portion) | Speed priority over completeness |
| Good Till Canceled | Yes | Until you cancel or fill completes | Patient limit orders |
| Day Order | Yes | End of trading day | Standard intraday trading |
Fill or kill orders are available on most institutional crypto exchanges and many retail platforms. They are particularly useful in low-liquidity token markets where order books are thin and large orders would move the market significantly. By using FOK, you ensure you either get the exact position at the exact price you need or you do not trade at all, which preserves your optionality to wait for better conditions.
Crypto market makers and arbitrageurs rely on FOK when executing multi-leg strategies across different exchanges. If one leg of a position cannot be filled in full at the required price, the entire arbitrage is invalidated, and placing partial fills would expose them to open risk that the strategy was designed to avoid.
Sources:
https://www.finra.org/investors/investing/investing-basics/how-to-place-trade
https://www.sec.gov/investor/pubs/trading-basics.htm
https://www.cboe.com/education/
With deep roots in traditional finance and the digital asset industry, Acquire.Fi operates as a specialist M&A advisory firm. Coverage spans M&A, secondaries, OTC, and capital markets advisory across digital assets and frontier tech. Our team has decades of combined experience across every stage of the deal lifecycle.
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