Fill-or-kill order

A fill-or-kill (FOK) order is an instruction that must execute completely and immediately at your specified price, or be canceled entirely. No partial fills, no waiting. If 10,000 shares are not available to buy or sell right now at your price, the entire order is killed. FOK is used by traders who want all-or-nothing execution or prefer to move on rather than split a large order.

How fill-or-kill works

When you place a FOK order, you are saying: “Fill my entire size right now at my price, or do not fill any of it.”

Example: You place a FOK order to buy 10,000 shares at $50.

• If there are 10,000 shares available to buy at $50 or better, your entire order fills immediately.
• If there are only 8,000 shares available at $50, and the next 2,000 are at $50.01, your entire order is canceled (killed). You get nothing.

This is an all-or-nothing constraint combined with an immediate-or-never timing constraint.

FOK vs. IOC (immediate-or-cancel)

Both FOK and IOC orders execute immediately or are canceled, but they differ on partial fills:

If you place a 10,000-share FOK at $50 and only 8,000 are available, you get 0 shares. If you place a 10,000-share IOC at $50, you get 8,000 shares.

FOK vs. AON (all-or-none)

FOK and all-or-none both require full size, but they differ on timing:

A FOK is “I want all 10,000 right now, or forget it.” An AON is “I want all 10,000, and I will wait for them.”

Practical use cases for FOK

Large block trades. An institution wanting to buy a large position might use FOK. “If I cannot get my entire block at my target price right now, I do not want a partial fill — I will look for liquidity elsewhere.”

Arbitrage trades. An arbitrageur might place a FOK to buy on one venue (if it executes the full size immediately). If the full size is not available, the arbitrage opportunity is likely gone anyway, so canceling the order is fine.

Market-maker inventory management. Market makers use FOK orders to avoid taking on unwanted partial inventory. “I want to sell 5,000 shares, all at once, at my price. If I can only sell 3,000, I will hold my inventory instead.”

Liquidity and FOK

FOK orders are only practical in highly liquid securities where your order size is small relative to available liquidity. For a large-cap stock like Apple, a 10,000-share FOK will likely execute. For a thinly traded penny stock, even a 1,000-share FOK might be killed.

Large institutions trading illiquid securities would never use FOK; they would use all-or-none and wait for the full size to accumulate.

FOK and broker support

FOK support varies by broker:

• Interactive Brokers: Fully supports FOK for stocks and many other instruments.
• Schwab, Fidelity, TD Ameritrade: Support FOK for stocks and some derivatives.
• Discount brokers: May not support FOK; check documentation.

If your broker does not support FOK, you can sometimes approximate it with a limit order combined with an all-or-none constraint and a very short time window (e.g., day order).

FOK orders and slippage

A FOK order with a limit price is somewhat protected: your order will only fill at your limit price or better. But a FOK order that is a market order (market-FOK) will execute immediately at whatever price the market offers. This can result in slippage if you are not careful.

Most FOK orders are limit orders, not market orders.

When NOT to use FOK

Small orders in liquid markets. If you are buying 100 shares of a large-cap stock, just use a regular limit order or market order. FOK is overkill.

When you want partial fills. If you are happy to get 80% of your order filled and move on, use an IOC order instead.

When you are patient. If you have time and want to ensure you get all your shares, use an all-or-none order and wait.

See also