Partial Fills: What Happens When Only Part of an Order Executes

You ordered 1 BTC, but only 0.4 BTC arrived. A partial fill is a normal order-book outcome. The risks arise afterward, when average price, fees, stop quantity and remaining orders differ from what you expected, often without an obvious warning.

Why a partial fill is normal

An order does not necessarily execute as one block. The exchange matches it against opposing orders in the order book. If less quantity is available at acceptable prices than you requested, only that amount fills and the rest remains. Unlike a completely unfilled order, a partial fill means a position already exists while part of the order is still open.

In this book, a market order would continue to 60,050 to fill the remaining 0.5, worsening the average price. That is slippage. The guide contrasts accepting possible partial fills with a limit order against accepting slippage with a market order.

Four situations that produce partial fills

IOC is easy to misunderstand. Among IOC and FOK order options, IOC permits partial execution and discards the remainder, while FOK executes nothing unless the entire quantity can fill. The same book can produce a 0.5 fill with IOC and no fill with FOK. Knowing the selected option explains the difference.

TWAP and iceberg orders deliberately split large orders to work with limited depth. Smaller pieces aim to protect average execution price instead of moving the book with one large order.

Average price and fees use only the filled quantity

The account reflects filled quantity, not requested quantity. The average entry price is the weighted average of executed pieces.

The problem begins when you take the next action as though the account holds the full requested 1 BTC.

The most dangerous trap: mismatched stop quantity

It is common to place a 1 BTC stop-loss immediately after submitting a 1 BTC entry. If only 0.5 BTC fills, the stop is twice the actual position.

The original guide describes excess quantity reversing the position in one-way mode or creating a short leg in hedge mode. Exact handling depends on the exchange, as noted below. The concern is that an exit becomes a new trade. Its proposed safeguard is Reduce-Only on closing, stop and take-profit orders. Reduce-only execution decreases the position and prevents excess quantity from creating a new one.

The same issue can affect staged take profits. If three exits were sized for a full entry but the entry filled only partially, the first exit may close everything and the remaining two may create new exposure. This is why the guide also uses reduce-only for take profits.

The remaining entry order is still active

A GTC, or good-till-canceled, remainder stays in the book. It can quietly fill hours later when price returns.

This is why you must check open orders separately after closing a position. Remaining orders can also reserve available margin and contribute to rejected new orders.

Conditions that make partial fills more common

Minimum order sizes can leave a remainder too small to process normally. The guide suggests canceling such residual quantity and submitting an appropriately sized order if needed.

What to check after submitting an order

The guide recommends the habit of confirming the fill and using the actual filled quantity when setting the stop. Presetting an exit alongside entry is convenient, but an unadjusted quantity can create the problems above.

Three key points

① Partial fills are normal when acceptable book depth is smaller than the order. The example contrasts limit-order fill uncertainty with market-order slippage.
② Average price and fees reflect executed quantity, while a preset stop or take-profit quantity may remain unchanged. Excess closing quantity can create an opposite position; reduce-only is the guide's safeguard.
③ A GTC remainder stays active and can fill later. Check open orders even after closing a position.

Caution

Order-book quantities, prices, sizes and fee rates are hypothetical examples, not measurements from a particular exchange or asset. Remaining-quantity handling, IOC/FOK behavior, reduce-only support, below-minimum remainders and excess exit orders in one-way or hedge mode vary by exchange. Verify the rules and order screen of the exchange you use. Leveraged trading can lose all principal. Decisions and their consequences remain your responsibility.