Why you should know this
A partial fill is easy to overlook. The trader may think, “My order is still open,” while already holding a position. Or they may think, “I bought,” while most of the intended quantity remains unfilled.
Execution discipline requires reconciling both truths. This lesson connects order-book depth with fees, position size and post-trade review.
What is a partial fill?
An order is partially filled when only part of its requested quantity executes.
If Lina submits a buy for 1,000 units and 350 execute:
- filled quantity: 350;
- remaining quantity: 650;
- current position created by this order: 350, subject to any other trades;
- order state: partly filled or equivalent venue label.
The remainder may stay open, cancel automatically or expire depending on order type and time-in-force.
Why partial fills happen
- Less opposite quantity is available at acceptable prices.
- Earlier orders are ahead at the same price.
- The market moves away.
- Time-in-force cancels the unfilled portion.
- The venue applies minimum, protection or system rules.
- The trader cancels while some execution is already in flight.
Partial execution is normal market behavior, not automatically an error.
Price priority
Under price-time priority, the best-priced eligible orders go first.
For buyers, a higher bid has priority over a lower bid. For sellers, a lower ask has priority over a higher ask.
If our buy is at ₱99 and another buyer bids ₱100, incoming sellers normally meet the ₱100 bid first.
Time priority
At the same price, the order accepted earlier is generally ahead.
Suppose 5,000 units are already bid at ₱100. We add a bid for 1,000 at ₱100. If 2,000 units of market selling arrive, the earlier queue may absorb all of it and our order may receive nothing.
Seeing trades at ₱100 does not prove the venue skipped us.
Queue position is uncertain
Public depth may show total quantity ahead, but cancellations, hidden instructions, self-trade prevention and matching details can alter outcomes. We may not know exact queue position from a retail screen.
Use it as an estimate. Product documentation controls the actual algorithm.
Weighted average fill
Lina’s 350-unit fill happens in two parts:
- 200 units at ₱100;
- 150 units at ₱100.50.
Average fill:
[(200 × 100) + (150 × 100.50)] ÷ 350 = ₱100.21 approximately.
Fees may differ by fill. If part took liquidity and the remainder later made liquidity, preserve each classification rather than applying one rate blindly.
The remainder decision
After a partial fill, choose deliberately:
- Leave the remainder open.
- Cancel it.
- Replace it at a new price.
- Accept the smaller completed position.
- Exit the partial position if the thesis or risk limit changed.
None is automatically correct. The choice depends on purpose, timing, queue, cost and current evidence.
Modification can change priority
Many matching systems treat price changes or quantity increases as a new priority event. Decreasing quantity may be handled differently. Exact rules vary.
Repeatedly moving an order to chase price can place it at the back of a new queue while increasing emotional pressure. Verify whether cancel-and-replace or modification changes order identity and priority.
Cancellation is a request, not time travel
An order can fill while a cancellation message travels. The screen may show “pending cancel” or update after another execution.
After cancellation, confirm:
- final order status;
- total filled quantity;
- average price;
- fees;
- available balance;
- any remaining open order.
Do not submit a replacement based only on the quantity you remember.
Time-in-force changes the remainder
- Good ’Til Canceled may leave it open.
- Immediate or Cancel should cancel the unfilled part after immediate execution.
- Fill or Kill should avoid partial execution if the venue implements it as described.
Names and behavior are product-specific. An article cannot prove a feature is available.
Risk created by a partial position
Suppose a plan requires 1,000 units to hedge another exposure, but only 350 fill. The hedge is incomplete. A speculative trader may also use a stop sized for 1,000 while holding 350, or later forget the open 650 and double the intended position.
Update risk controls to actual filled quantity, not intended quantity.
Practical crypto-to-PHP scenario
Miguel places a limit sell to convert crypto to PHP. Only 40% fills before the bid falls. He now holds two balances: PHP proceeds and remaining crypto.
He should reconcile both, calculate the actual blended rate, decide whether the remainder deadline matters and include Withdrawal costs. Chasing the remainder into a thin book may reduce the final PHP more than waiting—yet waiting carries price risk.
The lesson is coexisting with uncertainty, not pretending one choice eliminates it.
The FILL record
- F — Filled: exact executed quantity and average price.
- I — In queue: remaining quantity and current limit.
- L — Liquidity role: maker/taker per fill and fees.
- L — Limits: position, deadline and maximum cost after the partial result.
Keep this record before submitting another order.
Common mistakes
- Treating an open order as zero position.
- Applying one fee rate to mixed executions.
- Assuming trades at the limit mean our queue was reached.
- Replacing repeatedly without checking priority.
- Believing cancellation prevents all in-flight fills.
- Forgetting to resize stops or hedges.
- Submitting a duplicate order before reconciliation.
A no-money queue drill
Assume 1,000 units are ahead of your 500-unit sell limit at ₱10. Buyers take 1,200 at that price.
Estimate your fill under simple price-time priority. Then imagine you increased your quantity and lost priority before the trade. Write the possible change and the information still missing.
How this connects to market mastery
Partial-fill management is operational discipline. It forces us to separate intention from execution and to treat every status update as evidence.
Mastery is not always getting the full amount. It is preventing an incomplete execution from becoming an uncontrolled position.
Key takeaways and check
- Partial fills create both a position and a remainder.
- Better price ranks before worse price; earlier eligible orders commonly rank first at the same price.
- Average fill must weight every execution quantity.
- Modification and cancellation can affect priority and final quantity.
- Reconcile before replacing or resizing risk controls.
Developing Trader check: Reconcile Lina’s 350-unit fill, calculate its average price and list the five facts she should confirm before changing the 650-unit remainder.
*Cryptocurrency and virtual asset transactions are highly volatile and irreversible, may result in significant losses, and do not guarantee returns; customers should trade only after understanding the risks involved.
