Partial fill
A partial fill is the execution of only part of an order's quantity. The remainder keeps working at its price, is canceled if the order was immediate-or-cancel, or never existed if the order was fill-or-kill. Partial fills change the size, the average price and the protection of a position, which is why the broker's report, not the order sent, defines what is held.
Senzoukria · Glossary · Updated September 2026
Why only part of an order executes
- Queue position: under price-time priority, a resting limit order fills only as far as trading at its price reaches its place in line.
- Pro-rata allocation: on products that allocate by size, each resting order receives a share of an incoming order, rounded down.
- A marketable limit order that runs out of size within its limit fills partly and rests the remainder.
- An exchange protection range can stop a market order before its full quantity is filled.
- An IOC order keeps its partial fill and cancels the rest; an FOK order cannot be partially filled by definition.
A worked example
A trader bids for 10 contracts at 4,995.00 behind 300 contracts already resting there. Sellers hit 4,995.00 for 306 contracts, then buyers lift the market and price leaves the level. The first 300 contracts in the queue are filled, the trader receives 6, and 4 remain working at 4,995.00 while price moves away. The trader is long 6, not 10, and the fills arrived as sellers were pressing the level, which is the usual experience of passive orders: they fill most completely when the market trades through them.
Consequences for the position
- Exits must match the size actually held. A stop for 10 against a position of 6 would open a short of 4 if it triggers.
- The average price of the position is the volume-weighted price of the fills, not the price of the order.
- Risk per trade is computed on the filled size; a remainder that fills later changes it again.
- The unfilled remainder is a working order in its own right and must be canceled if the trade idea has changed.
In Senzoukria
The Working Orders table on the Trading page shows the order quantity with the filled quantity in parentheses once part of it has traded, together with the order's status and a Cancel button. The positions table shows the size held and its average price in the Avg column, and the desk's Protections stage lists the exit orders the broker reports for each position. The autopilot, after sending a market entry, waits up to 6 seconds for the complete fill; if it does not see it, it stops with the message 'no complete fill seen within 6s; position may be unprotected', disarms, cancels the orders it knows it sent and asks for the account to be verified, instead of attaching exits sized for a quantity it may not hold.
Related
- Working order
- Queue position
- Pro-rata matching
- Average fill price
- Bracket order
- Positions and working orders
In the same section
- Fill-or-kill order
- Immediate-or-cancel order
- Market order protection
- Marketable limit order
- Pass rate
- Parameter sweep
- Payoff ratio
- Parameter stability
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Frequently asked questions
- Can a market order be partially filled?
- Yes. If the book does not hold enough size, or if an exchange protection range stops the order, a market order can fill only part of its quantity; on CME the unfilled remainder of a market order with protection rests as a limit order at the edge of the protected range. An immediate-or-cancel instruction also produces partial fills by design.
- How should protective orders be handled after a partial fill?
- Size them to the quantity actually filled, as reported by the broker, and adjust them if the remainder fills later. Check that the stop and the target carry the same quantity as the open position, since a mismatch either leaves contracts unprotected or opens a new position in the opposite direction.