In plain English
What Partial fill means
Orders do not always transact as a single block. An execution venue may match some of the requested size with available counterparties and leave the rest open. Whether that remainder stays working depends on the order type and time-in-force instruction. For example, an immediate-or-cancel order takes what is available immediately and cancels the remainder, while a fill-or-kill order disallows partial execution.
Why it matters
A partial fill can leave a trader with a smaller position than intended, or with an unexecuted remainder exposed to later price changes. It also affects average execution price if different portions fill at different prices. For CFDs and retail forex, the availability and mechanics of partial fills depend on the provider’s execution arrangements and product terms.
Example
An order requests 100,000 units of EUR/USD at 1.08500 or better. Only 60,000 units are available at 1.08500, so those units execute. If the order remains active, the other 40,000 units might fill later at 1.08500 or better; if it is immediate-or-cancel, that remainder is canceled. The order is partially filled either way.
Quick answers
Common questions
Can a market order be partially filled?+
Yes. Depending on the market and broker’s handling, part of a market order can execute while the remaining quantity is filled at other available prices, canceled, or otherwise handled under the applicable order instructions.
How is the price of a partial fill reported?+
A platform may report each execution separately or show a volume-weighted average execution price. Traders should check the execution report because individual portions can execute at different prices.
Sources