What is a partial fill?
A partial fill happens when only part of the quantity you wanted to buy or sell is matched. The matched portion becomes a confirmed fill, while the unmatched portion remains subject to the order's current status and the available market.
This can happen with an order that asks for more shares or value than the available matching orders can provide at the relevant price. It is a normal execution outcome in a market with changing liquidity; it is not an indication that the entire order completed.
Why partial fills happen
Several execution conditions can combine to leave part of an order unmatched:
- Available liquidity: there may not be enough opposite-side quantity at the price levels the order can use.
- Limit price: a price limit can restrict which orders are eligible to match.
- Other orders in the book: competing orders may be matched first or may consume the quantity that was visible moments earlier.
- Price movement: bids and asks can change while an order is waiting or being processed.
- Order size: a larger order usually interacts with more price levels and has more quantity that can remain unmatched.
The important point is that a displayed price or a single level does not describe every unit of a larger order. The fill result has to be read from the confirmed quantity and the current remainder.
Example
| Order size | $1,000 |
|---|---|
| Confirmed filled | $640 |
| Remaining | $360 |
In this hypothetical example, the $640 portion has a confirmed execution record. The remaining $360 is a separate quantity that still needs an explicit current status; it should not be counted as filled.
What happens to the remainder?
The already executed portion and the remaining portion are different states. The filled part can have its own quantity, average price, and fee details. The remainder may still be open, may have been canceled, or may need a status check if the execution result is not yet confirmed.
A remaining quantity does not automatically inherit the result of the filled portion. Its ability to execute depends on the order's conditions and the market state at that moment.
What can happen next?
For an unmatched remainder, the available execution workflow can include:
- Wait while the remaining quantity stays open under its current conditions.
- Cancel the remaining quantity if the user no longer wants that open exposure.
- Review current execution conditions before deciding whether the existing remainder still makes sense.
These are distinct actions, not an instruction to choose one particular outcome. A clear interface should show the remainder and the action available next without silently placing a replacement order.
Why confirmed state matters
When reviewing an order, distinguish the state that has been confirmed from the state that is still changing:
| State | Plain-language meaning |
|---|---|
| Filled | That quantity has a confirmed match. |
| Open | Some quantity remains available to match under the order's conditions. |
| Canceled | The unfilled quantity is no longer working. |
| Unknown | The current result is not confirmed yet and needs a status check. |
This distinction is also useful when comparing the expected result with the actual result. The comparison should use confirmed fills, not an assumption that the original order size completed.
TickBetter and partial fills
TickBetter is being designed to make partial fills easier to understand and manage by clearly separating what has filled, what remains, and what action is available next.
The goal is a more inspectable execution workflow: see the original comparison, review the confirmed fill, identify the remainder, and verify the next available action. TickBetter is in development and is not a substitute for checking the current order state.