Partial Order Fills
A partial fill is when an order executes for less than its full size: part of the volume goes through, part remains. On liquid pairs in normal hours it is rare, and that is exactly why traders are unprepared for it.
When it happens
The cause is always the same: insufficient opposing volume at the required price. In practice this occurs in three situations: a size that is large for the instrument, a thin market during holidays and overnight hours, and the moments right after a release when liquidity providers temporarily withdraw quotes. On the majors at standard size it is uncommon; on exotics it is noticeably more frequent.
Why it is dangerous for risk calculation
The danger lies not in the fact itself but in the mismatch that follows. If the entry filled partially while the stop and target were set for the full size, then once the position closes a live order remains for a size that no longer exists — and it can open a new position in the opposite direction. The reverse case is no better: a partial fill on a stop leaves part of the position unprotected precisely when the market is moving against you.
What to check in your terminal
First, how linked orders behave on a partial fill: a correct implementation reduces their size automatically. Second, whether an option to forbid partial fills exists — it is not available everywhere, and enabling it means refusing the trade rather than accepting an incomplete entry. Third, the habit of reconciling actual position size against the plan after entry rather than assuming the order filled in full.
How to treat it
For most retail traders a partial fill is a rare scenario, but it belongs to the category of silent failures: nothing breaks, the terminal shows no error, and the position's risk profile is no longer what was planned. Checking the settings once and adding a size reconciliation to your entry checklist closes the question.
This material is educational and is not individual investment advice. Trading forex carries the risk of losing capital.
Frequently asked questions
Why did my order fill only partially?
Because there was not enough opposing volume at the required price. This happens most often with large size, in thin markets, or immediately after a data release.
Why are partial fills dangerous?
Because of size mismatch: a stop and target set for the full position can, after part of it closes, open a new trade in the opposite direction or leave a remainder unprotected.
Can partial fills be disabled?
Some terminals offer that option, which means refusing the trade rather than accepting an incomplete entry. Availability depends on the broker and account type.
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