All or None Orders

An all or none (AON) order is an instruction to fill the entire order in one go or not at all. Unlike a fill or kill order, it does not have to happen immediately: an AON order can wait, for the day or longer, until enough size is available at your price to complete it in full. It protects you from partial fills, at the cost of often waiting longer or missing the trade altogether.

How an AON order works#

AON compared with similar instructions#

See IOC and FOK Orders for the immediate versions.

Why someone would use AON#

• Avoiding small, costly partial fills. If your broker charges a commission per fill or per day, many small partial fills of the same order can add costs.
• Positions that only make sense at full size. For example, buying exactly enough shares to cover an options position or to complete a planned hedge.
• Odd lot issues. In some markets, a leftover small piece of a position can be awkward or expensive to trade later.

The drawbacks#

1. Lower priority. Because an AON order cannot accept a partial fill, it is often passed over by the market. Other orders at the same price can fill ahead of yours.
2. Missed trades. Your price can trade all day in small pieces without your order ever completing.
3. Limited availability. Many venues and brokers no longer support AON for stocks, or only for certain order types. Some exchanges handle it differently from others.
4. Not useful for liquid markets. In heavily traded stocks, partial fills are rare for normal size orders anyway, so AON adds little.

Alternatives to AON#

• Normal limit orders, accepting partial fills and adjusting your stops and size accordingly.
• Minimum quantity instructions, offered on some platforms, which require a minimum fill size per execution rather than all of it.
• Iceberg orders that show only part of a large order. See Hidden and Iceberg Orders.
• Algorithmic execution that works a large order over time. See VWAP, TWAP and POV Execution.

AON in other contexts#

The term also appears in securities offerings, where an underwriter agrees to sell an entire issue or cancel it. And in options trading, some brokers allow AON on multi leg orders so that all legs fill together. Most modern platforms fill multi leg spreads as a single package automatically.

Frequently asked questions#

What does all or none mean in trading?#

It means the order must be filled in full in a single execution, or not at all. It can stay open and wait for enough size at your price.

Why is my all or none order not filling?#

Because no single seller or buyer has offered enough size at your price, or other orders have priority. AON orders often fill less frequently than normal orders.

Is AON the same as fill or kill?#

No. Fill or kill must fill completely and immediately. AON must fill completely but can wait.

Sources#

• Wikipedia, All or none