Immediate-or-Cancel (IOC)

What Is an Immediate-or-Cancel Order?

An immediate-or-cancel (IOC) order fills as much as possible right now at the specified price or better, cancelling whatever cannot be filled immediately. The order doesn’t rest in the book — it executes against available liquidity and any remainder vanishes.

The critical distinction from fill-or-kill: IOC accepts partial fills. An IOC order for 500 contracts that finds only 150 available fills 150 and cancels the remaining 350. You get a position — just not the full size.

Why It Matters for Options Traders

IOC balances speed and flexibility. Traders who want a position immediately but don’t require exact quantity use IOC over resting limit orders.

The advantage over fill-or-kill is higher fill probability in thin markets. Options often carry fragmented liquidity across strikes and expirations. A FOK order for 500 contracts fails entirely if only 150 are available. An IOC captures those 150 and provides immediate partial exposure.

Common IOC uses:

• Moderately liquid markets where full fill is likely but not guaranteed
• Slippage management by capping price while demanding fast execution
• Avoiding book exposure — the order doesn’t sit visible where market makers can adjust around it
• Algorithmic execution — systematic strategies use IOC to probe liquidity without leaving footprints

The downside is size uncertainty. A strategy designed for 1,000 contracts may not work as modeled with 340. Traders using IOC must account for partial fill risk in sizing and risk management.

Key Characteristics

• Immediate execution: The order acts on available liquidity the moment it arrives — no waiting
• Partial fills allowed: Unlike fill-or-kill, IOC accepts whatever quantity is available at the price
• Remainder cancelled: Any unfilled portion is cancelled, never resting in the book
• Price discipline: As a limit-style instruction, the price cannot be crossed — the trader controls the worst acceptable price
• No book visibility: IOC orders do not appear in the public order book, reducing information leakage
• Speed vs. size tradeoff: Faster execution than working a limit order over time, but no guarantee of full size