Partial Fill
Also known as: partial execution
What is it?
A partial fill is when only part of the size you ordered actually gets executed, because there was not enough trading interest available at your price to satisfy the whole order. Imagine you place an order to buy five lots, but at the price you wanted, the market only had enough sellers for three lots. Three lots fill, and the remaining two are left unfilled, waiting, cancelled, or filled later at a worse price, depending on the order type. You ended up with a smaller position than you planned.
This happens because every price level in the market has a limited amount of size available, and a large order can simply exhaust what is on offer. Partial fills are most common when you trade big size, or when you trade thin instruments and quiet hours where liquidity is sparse. For a trader, the danger is subtle but real: most strategies and risk calculations assume the full position got filled. If only sixty percent of your order executed, your actual exposure, your stop-loss distance in money terms, and your position-sizing maths are all quietly off from the plan.
You might think you are risking a fixed amount when in fact you are risking less, or you might leave the unfilled remainder dangling and accidentally double up if it fills later. Knowing partial fills can happen lets you decide in advance whether to complete the remainder, cancel it, or break large orders into smaller pieces that the market can absorb cleanly.
Why it matters: A partial fill leaves you with a smaller position than planned, throwing off sizing and any rules that assume the full lot.
Partials change your actual position size, which knocks risk and target maths off the plan.
Real-world example
An order for 5 lots fills only 3 because that is all the liquidity at the price, leaving 2 lots unfilled.
How SignalBots handles it
SignalBots surfaces partial-fill outcomes so your position size reflects what truly executed, not what was requested.
Pro tip
On larger sizes in thinner instruments, expect partials and decide in advance whether to complete or cancel the remainder.
Common pitfalls
Assuming every order fills in full, so position-size and risk calculations are quietly wrong after a partial.
Frequently asked questions
Why did my order only partly fill?
There was not enough liquidity at your price to satisfy the full size. The part that could fill did, and the rest waits, fills at a worse price, or cancels, depending on the order type and the broker's rules.
What happens to the part that did not fill?
It depends on the order. The remainder may stay pending until liquidity appears, fill at a worse price as the order walks up the book, or be cancelled outright. Knowing your broker's behaviour in advance prevents surprises.
Does a partial fill mess up my risk?
It can. If you planned to risk a fixed amount on a full position but only part filled, your actual exposure and the money value of your stop are smaller than intended. Always check the filled size before trusting your risk maths.
How do I avoid partial fills?
Trade liquid instruments during active hours, keep individual order sizes within what the market can absorb, and split very large orders into smaller pieces. Thin instruments and quiet sessions are where partials happen most.
Are partial fills a sign of a bad broker?
Not on their own. They reflect available liquidity at your price, which no broker controls. Persistent partials on small orders in liquid markets, however, can point to a broker or routing problem worth investigating.