Partial Fill
When only part of your order executes and the rest stays open or is canceled.
Also called: partially filled
Written by Javier Sánchez Ros
In plain language
Partial fills happen when there is not enough size available at your price. You get what was there; the remainder waits, or is canceled depending on the order’s time in force.
This leaves you with a smaller position than planned, which quietly changes your risk. Half the intended size means half the intended risk — and half the intended reward.
They are common in illiquid instruments, in large orders, and with immediate-or-cancel instructions.
Worked through
An order for 1,000 shares that fills 340
- Ordered
- 1,000 shares
- Filled
- 340 shares
- Risk actually taken
- 34% of planned
- Stop order still sized for
- 1,000
The price came to the limit, took 340 shares, and moved away. The position is real but it is a third of the intended size, and every number attached to it is now wrong: the risk is a third of plan, the profit at target is a third, and the protective stop — if it was entered separately for the full amount — is sized for a position that does not exist.
That last part is the dangerous one. A stop for 1,000 shares against a 340-share position will close the 340 and open a 660-share short, in exactly the way a stale one-cancels-other leg does.
The decision itself is genuinely awkward. Complete the position at a worse price and the average entry moves against you, widening the real stop distance. Leave it at 340 and a correct call pays a third of what the analysis was worth. Neither is wrong; what is wrong is not noticing.
The habit that prevents all of it: before doing anything else, read what actually filled, and make the exits match that number rather than the number you typed.
Why it matters
A partially filled entry paired with a full-size stop calculation means your position no longer matches your plan in either direction.
Common mistakes
- Assuming the whole order filled and managing the trade at the wrong size.
- Chasing the unfilled remainder at a worse price, ruining the average entry.
Keep exploring
These concepts are connected. Understanding one usually makes the next one easier.
The actual execution of an order, at the price and quantity you really received.
How easily an asset can be bought or sold without moving its price.
The instruction that says how long an order stays active before it expires.
An order to buy or sell at a specified price or better — it may not fill at all.
The amount of an asset you buy or sell in a single trade.