AON vs. FOK orders
Also known as: all or none vs fill or kill, all-or-none order, fill-or-kill order
An all-or-none (AON) order must be filled in its entirety but can stay open until it is, while a fill-or-kill (FOK) order must be filled in its entirety immediately or it is cancelled. Both forbid partial fills; only FOK adds the immediacy requirement.
All-or-none and fill-or-kill are both order qualifiers that prohibit partial execution. If a customer enters an order for 10,000 shares with either qualifier, a fill of 4,000 shares is not acceptable — the order goes through for the full 10,000 or not at all. What separates them is time.
An AON order stays alive. It can be entered as a day order or good-til-cancelled, and it simply waits until enough contra-side interest appears to fill the whole quantity at once. A FOK order gets one shot: if the entire quantity cannot be executed the moment it reaches the market, the order is killed outright and the customer is notified.
A third qualifier, immediate-or-cancel (IOC), rounds out the set and is the easiest way to keep the logic straight. IOC demands immediacy but permits a partial fill, cancelling whatever cannot be executed right away. So AON requires the full amount without immediacy, IOC requires immediacy without the full amount, and FOK requires both. Traders reach for AON when the size matters more than the timing — an odd position that would be awkward to hold half-filled — and for FOK when a fleeting price is the whole point of the trade.
These qualifiers show up throughout the securities licensing sequence. The SIE covers them under additional order specifications, and the Series 7 revisits them alongside held and not-held orders. Exam questions typically describe a scenario with a partial fill available and ask which qualifier would have produced an execution, so knowing the immediacy-versus-quantity split is usually enough to answer correctly.
Key takeaways
- AON and FOK both prohibit partial fills — the order executes in full or not at all.
- An AON order can remain open until the full quantity can be filled.
- A FOK order is cancelled immediately if the full quantity cannot be executed at once.
- Immediate-or-cancel (IOC) demands immediacy but does allow a partial fill.
- Think of FOK as AON plus immediacy.