Fill-or-Kill Orders¶
OVERVIEW¶
A fill-or-kill (FOK) order instructs the market to fill the entire requested quantity immediately at the limit price or better — or cancel the order outright with zero shares executed. No partial fills occur, no portion rests on the book, and no second attempt is made.
FOK combines two independent order conditions simultaneously:
| Condition | Behavior |
|---|---|
| All-or-None (AON) | Full quantity or nothing — no partial fills |
| Immediate-or-Cancel (IOC) | Execute now or cancel — no resting on the book |
| Fill-or-Kill (FOK) | Both conditions enforced simultaneously |
Note
FOK, AON, and IOC produce meaningfully different fill behavior. Confusing them results in unintended execution outcomes. See the comparison table under Order Type Differences below.
HOW IT WORKS¶
When a FOK order is submitted, the exchange or ECN evaluates the full requested size against the visible (and, on some venues, hidden) order book at that exact instant.
- Full size available at limit price or better → entire order fills in one transaction
- Even one share short of requested size → entire order is canceled, zero shares execute
Order Type Differences¶
| Order Type | Partial Fill Allowed | Rests on Book | Immediacy Required |
|---|---|---|---|
| FOK | No | No | Yes |
| IOC | Yes | No | Yes |
| AON | No | Yes | No |
| Limit | Yes | Yes | No |
| Market | Yes | No | Yes |
Worked Example¶
A trader submits a FOK order to buy 5,000 shares at $2.05 or better. At the moment the order reaches the book, 3,200 shares are available at $2.05 and better.
| Scenario | Order Type | Result |
|---|---|---|
| 3,200 of 5,000 shares available | FOK | 0 shares filled — order killed |
| 3,200 of 5,000 shares available | IOC | 3,200 shares filled, 1,800 canceled |
| 3,200 of 5,000 shares available | Limit | 3,200 shares filled, 1,800 rests on book |
Tip
FOK is most effective on liquid names where the full order size is realistically available at a single instant. On thinly traded instruments, expect frequent order rejections.
FEATURES¶
Leg Risk Protection¶
FOK-style logic is the standard approach for multi-leg options strategies where each leg's risk profile depends on all other legs filling together.
- Iron condors — four legs must fill simultaneously or none should
- Vertical spreads — partial fills leave unintended naked exposure
- Calendar spreads — mismatched fills produce unintended directional risk
Note
Leg risk refers to the danger of holding a filled leg while remaining legs go unfilled, resulting in an unintended and potentially unhedged position.
Institutional Block Execution¶
Institutional traders use FOK to avoid signaling intent. A small partial fill on a large order reveals the presence of a large buyer or seller to the market without accomplishing the objective of establishing the full position.
Smart Order Routing Integration¶
Algorithmic execution systems use FOK as a building block within smart order routing (SOR) logic — probing available liquidity at a venue without leaving a resting order exposed to adverse selection or queue position deterioration.
HOW TO USE¶
When to Use FOK¶
Use a fill-or-kill order when:
- A partial fill creates more risk than no fill at all
- You are executing a multi-leg strategy that requires simultaneous fills across all legs
- You are testing liquidity at a specific price level without leaving a resting order
- You are an institutional or algorithmic trader managing information leakage on large block orders
When Not to Use FOK¶
| Situation | Better Alternative |
|---|---|
| Building or exiting a position gradually | Good-Til-Canceled limit order |
| Trading illiquid or thinly traded names | Work order in smaller clips |
| Acceptable with partial fills | IOC order |
| Full size required but timing is flexible | AON order |
Platform Availability¶
Note
FOK support is inconsistent across retail brokerage platforms. Many platforms expose FOK only through API or algorithmic order routing interfaces rather than the standard order ticket. FOK is used primarily by institutional and program trading desks. Confirm FOK availability with your broker or platform documentation before building strategies that depend on it.
KEYBOARD SHORTCUTS¶
| Action | Shortcut |
|---|---|
| Open order entry panel | O |
| Toggle order type selector | T |
| Select Fill-or-Kill | F then K |
| Set limit price field | P |
| Set quantity field | Q |
| Submit order | Enter |
| Cancel pending order | Escape |
Tip
Use the order type toggle shortcut T to cycle through FOK, IOC, and AON before submission to confirm the correct condition is selected. Verify the order type label displayed in the order preview before hitting Enter.