Partial FillAON
A partial fill happens when only part of your order is executed, usually because there was not enough volume available at your price.
A partial fill means only part of your order traded. It happens when there is not enough size at your price. The rest may stay open, be cancelled, or never have been allowed to trade, depending on the order instructions you chose.
- Category
- Order Types
- Reading time
- 3 min
- Also called
- Partial execution, Partially filled order
- Updated
Partial fills in plain words
If only some of the shares you want are available, the broker may fill just that part — a partial fill.1
Special instructions change this: a fill-or-kill (FOK) order must be executed in full straight away, or not at all.2
An all-or-none (AON) order also blocks partial fills, but it doesn't have to execute immediately like an FOK.1
How partial fills happen and what to do
Send the order
For example, a limit order for a set size.
Not enough size
If only part of the order can be matched, you may receive just that portion.1
Rest stays open
The remainder waits, unless you chose otherwise.
Use IOC to cancel the rest
With immediate-or-cancel (IOC), whatever can't be filled straight away at your price is cancelled.1
Use FOK for all-now
An FOK order eliminates that possibility.1
Use AON for all-later
An AON order that can't fill right away stays open until it fills or you cancel it.2
Worked examples
Example 1 — Limit buy
200 of 500Hypothetical buy limit 500 shares at 12.00; 200 trade at that price.
| Filled | 200 |
| Open | 300 |
Only part of the shares were available, so only part of the order was filled.1
Example 2 — IOC
Rest cancelledSame order sent as IOC.
| Filled | 200 |
| Cancelled | 300 |
Not enough shares were available at the limit price, so the IOC order cancelled the rest.1
Example 3 — Fees
−3.00Hypothetical broker charges 1.00 per execution; a 400-share order fills in 3 pieces over 3 days.
| Fees | 3 × 1.00 = 3.00 |
AON orders prevent partial filling of orders, which can avoid repeated per-fill charges.1
Order instructions and partial fills
| Aspect | Allows partial fill? | Rest of order |
|---|---|---|
| Standard limit | Yes | Stays open |
| IOC | Yes | Cancelled |
| FOK | No | All cancelled |
| AON | No | Waits |
Where partial fills show up
Limits
Common with a Limit Order.
Thin markets
Low Liquidity.
Duration
Set by Time-in-Force: IOC, FOK and GTC.
Sizing
Affects Position Sizing.
Advantages and disadvantages
Advantages
- You still get some of the trade.
- Better than no fill in fast markets.
- Instructions let you control it.
Disadvantages
- Position may be smaller than planned.
- Some brokers charge per fill.
- Leftover orders can be forgotten.
- AON and FOK may not fill at all.
Going deeper
Read as far as you need. Each level builds on the one before it.
Definition
Beginner
A partial fill simply means the broker filled whatever part of the order was available.1
FOK and IOC
Intermediate
FOK fills everything at once or nothing; IOC fills what it can at once and cancels the rest.1
AON
Advanced
AON insists on a complete fill but, unlike FOK, can wait.1 Instruction names and availability differ by broker and country.
Common mistakes
Forgetting the open remainder
Check open orders.
Sizing stops on the full order
Size to what filled.
Using AON in thin stocks
It may never fill.
Ignoring per-fill fees
Read the fee schedule.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- A partial fill is part of an order trading.
- Caused by limited size at your price.
- IOC cancels the rest.
- FOK is all now or nothing.
- AON waits for the full size.
Frequently asked questions
Is a partial fill bad?
Can market orders fill partly?
Will the rest fill later?
Further learning
- Time-in-Force: IOC, FOK and GTC
Order instructions.
- Liquidity
Why size runs out.
- Order Book
Depth at each price.
- Limit Order
The usual cause.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- FINRA. Trading Terms: Time Parameters and Qualifiers on Stock Orders (opens in a new tab) Checked .
- Investor.gov (SEC). Understanding Order Types – Investor Bulletin (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.