Why Was My Stock Order Only Partially Filled?

Your stock order was partially filled because enough eligible shares were available to execute only part of the requested quantity. The completed shares are final trades, while the unfilled balance may remain active, expire, or be canceled depending on the order type, time in force, session, and broker rules. Before submitting another order, confirm the cumulative filled quantity and whether the remaining shares are still working. Otherwise, both orders may execute and create a larger position than intended.

Key takeaway: Partially filled does not mean the order failed. It means at least one execution occurred, but the original quantity has not been completed.

What a partial fill actually means

A stock order can produce several separate executions rather than one transaction for the entire requested quantity.

Suppose a trader submits an order for 1,200 shares. The order receives:

1. 300 shares in the first execution;
2. 200 shares in the second execution;
3. no additional eligible liquidity.

The order state is now:

1. original quantity: 1,200 shares;
2. cumulative filled quantity: 500 shares;
3. remaining quantity: 700 shares;
4. status: partially filled.

The 500 executed shares cannot normally be canceled. Only the remaining 700 shares may still be available for cancellation or replacement.

This distinction is also reflected in exchange order-reporting systems. Nasdaq’s FIX specification separates:

1. OrderQty: original order quantity;
2. CumQty: quantity already executed;
3. LeavesQty: quantity still open for further execution;
4. AvgPx: average price across completed executions.

For an active order, the basic relationship is:

Remaining quantity = Original quantity − Cumulative filled quantity

The terminology shown to a retail trader can differ by broker, but the underlying state is similar. Nasdaq Trader: FIX Interface Specification

Partial-fill order-state flow

The practical order lifecycle is:

Order submitted: 1,200 shares

→ First fill: 300 shares

→ Cumulative filled: 300

→ Remaining: 900

→ Status: partially filled and working

→ Second fill: 200 shares

→ Cumulative filled: 500

→ Remaining: 700

→ Status: partially filled and working

The remaining 700 shares can then follow one of four paths:

1. additional executions complete the order;
2. the balance stays open at the permitted price;
3. the balance expires under its time-in-force instruction;
4. a cancellation request succeeds and removes the balance.

A platform may also display canceled/partially filled. That status means part of the order executed and the remainder was canceled. It does not mean that a live order still exists.

Why only part of the order executed

There was not enough eligible liquidity

The most direct explanation is that fewer shares were available than the quantity requested.

Assume a trader enters a limit order to buy 1,000 shares at $20 or lower. At that moment, eligible sellers offer:

1. 250 shares at $19.98;
2. 300 shares at $20;
3. all remaining offers above $20.

The order can execute 550 shares because those shares satisfy the limit. The remaining 450 shares cannot be purchased above $20 without violating the order’s price instruction.

The result is:

1. 250 shares filled at $19.98;
2. 300 shares filled at $20;
3. 450 shares still open at a $20 limit;
4. average execution price for the completed portion: $19.9909.

A displayed quote represents a specific quantity, not an unlimited supply of shares. Investor.gov notes that prices can change while an order travels through the execution process and that quotes are available only for a particular number of shares. Investor.gov: Executing an Order

Other orders were ahead in the queue

Available shares are not automatically allocated to every order at the displayed price. Other orders may already have priority.

A trader may see 2,000 shares offered at $30 and enter a limit order to buy 1,000 shares at $30. However, other eligible buy orders may already be waiting at that price.

If sellers provide only 2,400 shares before the offer disappears, the earlier orders could consume most of that liquidity. The trader might receive only 200 shares even though the chart shows multiple trades at $30.

The exact priority rules depend on the venue and order type. Price and time are common factors, but special order attributes and venue rules can affect the sequence.

Fidelity’s extended-hours disclosure explains that orders at each price are generally handled in the order received and that orders already on the ECN can prevent a later order from executing fully or partially. Fidelity: Extended-Hours Order Handling

A partial fill therefore does not prove that a broker ignored sufficient liquidity. The trader must consider:

1. how much executable size was available;
2. how much size was ahead of the order;
3. when the order reached the venue;
4. whether the displayed quote remained available;
5. whether the order was eligible to interact with that liquidity.

The market moved after the first execution

An order can begin executing and then stop because the market moves away from its price.

Suppose a trader enters a sell limit for 800 shares at $42 or higher.

The order receives:

1. 300 shares at $42.02;
2. 200 shares at $42.

The highest bid then falls to $41.90.

The completed 500 shares remain sold. The remaining 300-share sell limit cannot execute against a $41.90 bid because the trader required $42 or higher.

If the bid returns to $42 while the order remains active, additional executions may occur.

The order was divided across several executions or venues

A broker can route an order to an exchange, market maker, alternative trading system, or another execution venue. The entire requested quantity does not necessarily execute in one place or against one counterparty.

Investor.gov explains that an online order first reaches the broker, which then determines where to send it for execution. Investor.gov: Executing an Order

An order may consequently receive:

1. several fills on one venue;
2. fills from different venues;
3. different prices for different portions;
4. a temporary partial status while routing continues.

Investor.gov gives the example of a 1,000-share market order in which 500 shares execute at one price and the remaining 500 at a higher price in a fast market. Investor.gov: Understanding Order Types

The broker should display an average execution price based on all completed fills. The average should be calculated as a share-weighted figure:

Average execution price = Total value of completed fills ÷ Total shares filled

Extended-hours liquidity was limited

Partial fills are more likely when fewer market participants are trading or when available size is fragmented.

FINRA identifies lower liquidity and higher volatility as risks of extended-hours trading. It also notes that order-type availability can differ outside regular trading hours. FINRA: Time Parameters and Qualifiers on Stock Orders

A premarket order for 2,000 shares may receive only 150 shares even if the same stock normally trades millions of shares during the regular session. Total daily volume does not establish how much executable liquidity was available at the trader’s limit, venue, and timestamp.

The unfilled balance may also be canceled when the extended session ends, depending on the broker and selected time in force.

What happens to the remaining shares

The answer depends primarily on the order’s time in force and its final status.

Day order

The broker can continue trying to fill the remaining quantity during the order’s eligible trading day or session.

A partially filled day order can therefore receive additional executions later. If the balance remains unfilled when the applicable session ends, it normally expires.

Session eligibility matters. A day order entered for regular trading does not necessarily continue into after-hours trading. An extended-hours day order may apply only to the particular extended session.

The exact cutoff and session treatment are broker-specific.

Good-’til-canceled order

The remaining quantity can continue working after the day of entry, subject to:

1. the broker’s maximum GTC duration;
2. session eligibility;
3. corporate actions;
4. trading halts;
5. price or risk controls;
6. customer cancellation.

Fidelity notes that larger limit orders can fill completely or partially and may require more than one trading day unless another execution condition is selected. Fidelity: Order Types and Conditions

A GTC order should not be treated as permanent. Brokers establish their own expiration periods and may cancel orders under specified conditions.

Immediate-or-cancel order

An immediate-or-cancel order attempts to execute immediately. Any available portion may fill, while the unfilled balance is canceled.

For example:

1. order quantity: 1,000 shares;
2. immediately available quantity: 350 shares;
3. result: 350 shares filled and 650 canceled.

No working 650-share balance remains after the IOC instruction completes.

Both Fidelity and Charles Schwab describe IOC orders as allowing immediate partial execution while canceling the unfilled remainder. Fidelity: Trading FAQs—Order Types, Charles Schwab: Stock Order Types and Conditions

Fill-or-kill order

A fill-or-kill order requires immediate execution of the entire quantity. If the full amount cannot execute, the order is canceled.

A correctly processed FOK order should not produce an ordinary partial-fill outcome. Investor.gov: Fill-or-Kill Order

All-or-none order

An all-or-none instruction requires the entire quantity to execute together. Unlike FOK, it does not necessarily require immediate execution.

Availability and handling differ among brokers and venues. Fidelity also warns that an AON order can remain unexecuted even when the stock trades at the specified price if the entire requested quantity is not available. Fidelity: Trading FAQs—Order Types

Qualifiers that prevent partial fills can therefore increase non-execution risk.

Complete scenario: a partial fill and duplicate order

The following example is hypothetical.

A trader wants to buy 1,200 shares of XYZ and enters:

1. order type: buy limit;
2. quantity: 1,200 shares;
3. limit price: $25;
4. time in force: day;
5. eligible session: regular market.

First execution

At 10:15:00 a.m. ET, eligible sellers provide:

1. 300 shares at $25;
2. remaining offers above the limit.

The trader receives:

1. last fill: 300 shares at $25;
2. cumulative filled: 300 shares;
3. remaining quantity: 900 shares;
4. status: partially filled.

Second execution

A seller then offers 200 shares at $24.99.

The order receives another execution:

1. last fill: 200 shares at $24.99;
2. cumulative filled: 500 shares;
3. remaining quantity: 700 shares.

The average price of the completed portion is:

[(300 × $25) + (200 × $24.99)] ÷ 500 = $24.996

The remaining 700-share limit order continues working at $25.

The market moves away

The best offer rises to $25.08. No seller is currently willing to sell at $25 or lower.

The trader now owns 500 shares—not 1,200—and still has an active order to buy 700 shares at $25.

The dangerous response

The trader assumes the first order has stopped and submits a new order to buy 700 shares at $25.08 without canceling the original balance.

The new order fills immediately. The trader now owns the intended 1,200 shares:

1. 500 shares from the original order;
2. 700 shares from the new order.

However, the original 700-share order at $25 is still active.

Thirty minutes later, XYZ falls back to $25. The original balance fills.

The final position becomes:

500 + 700 + 700 = 1,900 shares

The trader intended to own 1,200 shares but now owns 700 excess shares because the substitute order did not automatically cancel the remaining quantity.

Fidelity explicitly states that submitting an identical or replacement order does not automatically cancel the previous order. The original must be canceled or replaced through the supported process. Fidelity: Trading FAQs—Placing Orders

The safer sequence

Before submitting another order, the trader should:

1. Confirm the cumulative fill: 500 shares.
2. Confirm the active balance: 700 shares.
3. Submit a cancellation request for the remaining balance.
4. Wait for verified cancellation.
5. Recheck the position because another execution could occur while cancellation is pending.
6. Calculate the quantity still required.
7. Submit a new order only for that confirmed difference.

A broker-supported cancel-and-replace workflow can coordinate these actions, but it still operates subject to previous executions and broker rules.

Fidelity explains that a replacement order is sent after the original receives a verified cancel status. It also warns that cancellation requests are handled on a best-efforts basis and can be preceded by another execution. Fidelity: Trading FAQs—Placing Orders

What to check before changing a partially filled order

1. Confirm the actual position

Check the position rather than relying only on an order notification.

Verify:

1. shares owned or sold short;
2. pending settlement activity;
3. filled quantity;
4. average execution price;
5. individual execution reports.

A delayed notification or stale order screen can create confusion about the current exposure.

2. Find the cumulative and remaining quantities

Record:

1. original order quantity;
2. cumulative filled quantity;
3. remaining quantity;
4. last fill quantity;
5. last fill price;
6. average execution price.

The most important number for the next decision is the remaining active quantity—not the original order size.

3. Identify the final order status

Distinguish among:

1. partially filled and working;
2. pending cancellation;
3. canceled/partially filled;
4. expired/partially filled;
5. completely filled;
6. rejected balance;
7. held or suspended.

A partially filled order can have no active remainder if the balance has already expired or been canceled.

4. Check the executable market

For a buy order, compare the limit with the current ask.

For a sell order, compare the limit with the current bid.

Also check:

1. available size;
2. spread;
3. recent executions;
4. whether the security is trading;
5. session eligibility;
6. any halt or reopening condition.

The last price alone does not show whether enough eligible shares are currently available to complete the order.

5. Check the time in force

Determine whether the balance is:

1. day;
2. GTC;
3. IOC;
4. FOK;
5. all-or-none;
6. subject to a session-specific instruction.

The same partial execution can produce very different outcomes depending on this setting.

6. Decide whether to leave the balance active

Leaving the order unchanged may allow it to retain its existing position in the relevant venue’s queue, although routing and venue handling can differ.

The risks are:

1. the order may fill later when the trader no longer wants it;
2. the market may move away and leave the balance unexecuted;
3. the trader may forget that the order remains active;
4. another order may duplicate the intended exposure.

7. Treat cancellation as a request until confirmed

A cancellation acknowledgement does not always mean the order is already canceled.

Fidelity states that open and partially filled orders can generally be submitted for cancellation, but attempts are performed on a best-efforts basis. The original order can execute while the cancellation remains pending. Fidelity: Orders Help

Do not assume the remaining quantity has disappeared until the platform shows a final canceled status.

8. Recalculate before submitting a replacement

Use:

Replacement quantity = Target final position − Confirmed current position − Other active eligible orders

This formula requires current information. If another partial execution occurs while a cancellation is pending, the replacement quantity must be reduced.

9. Understand the queue effect of changing the order

Changing an order is commonly processed as a cancellation and replacement. The replacement may receive a new queue position.

Fidelity warns that changing an extended-hours order can cause it to lose time priority. Fidelity: Extended-Hours Order Handling

Lowering the buy limit, raising the sell limit, or changing the size can therefore alter both marketability and priority. The exact treatment depends on the venue and modification.

10. Preserve evidence if the order does not reconcile

Save:

1. original order ticket;
2. order identifier;
3. submission timestamp;
4. every execution report;
5. cumulative filled quantity;
6. remaining quantity;
7. cancellation request;
8. verified cancellation or rejection;
9. position before and after the event;
10. applicable session and TIF;
11. screenshots of the bid and ask.

A precise request to broker support would be:

“Please reconcile the original order quantity, every partial execution, cumulative filled quantity, remaining quantity, average execution price, current order status, cancellation or replacement timestamps, routing venues, and whether the remaining balance is still eligible to execute.”

Hi2morrow methodology: We diagnose a partial fill in this order: original quantity → individual executions → cumulative filled quantity → remaining quantity → current position → active order status → limit price → executable bid or ask → time in force → session eligibility → cancellation status → replacement quantity.

When the standard explanation may not be enough

The order was canceled after the partial execution

If the status is canceled/partially filled, the executed portion remains valid but the unfilled balance is no longer working.

Possible causes include:

1. a successful customer cancellation;
2. IOC treatment;
3. session expiration;
4. an exchange or broker cancellation;
5. a corporate action;
6. an abnormal market condition;
7. a system or risk-control action.

The activity history should identify the cancellation reason where available.

Trading was halted

An order can receive a partial execution immediately before a halt. The remaining quantity might stay open, be held, or be canceled depending on the order, venue, and broker.

If it remains active, it may become eligible after trading resumes. The reopening price can be materially different from the previous execution price.

Do not submit a duplicate order merely because the remaining balance cannot trade during the halt.

The order belongs to a bracket, OCO, or conditional structure

A partial fill can affect attached orders.

Depending on the broker and configuration, linked orders may be:

1. resized;
2. activated proportionately;
3. left unchanged;
4. canceled;
5. held until the primary order completes.

Interactive Brokers, for example, documents OCA configurations in which a partial fill reduces the quantities of related orders. This is a broker-specific example, not a universal rule. Interactive Brokers: One-Cancels-All Orders

Inspect every parent and child order. Otherwise, a partially filled entry combined with full-sized exit orders can create unintended exposure.

The remaining quantity was rejected

A partial execution can be followed by rejection or cancellation of the balance because of:

1. buying-power limits;
2. short-sale restrictions;
3. unavailable borrow;
4. invalid order attributes;
5. venue restrictions;
6. risk controls;
7. corporate actions;
8. a change in security eligibility.

This is different from an ordinary working limit order waiting for liquidity. The broker’s rejection or cancellation code controls the diagnosis.

An execution was corrected or broken

Rarely, a previously reported execution can be corrected or canceled by the venue. The cumulative quantity and average price may then change.

Compare final execution reports and account activity instead of relying solely on the first notification.

The order used a minimum-quantity condition

A minimum-quantity instruction changes the normal execution process.

Charles Schwab explains that a minimum-quantity order requires at least the specified number of shares to be available before an execution can occur. It also notes that a quantity available across several venues may not satisfy a single-venue minimum. Charles Schwab: Stock Order Types and Conditions

This condition can reduce small partial fills but also increase the chance of no execution.

The trader believes a partial fill proves poor execution

A partial fill alone does not establish that the broker violated its obligations.

FINRA Rule 5310 requires firms to make every effort to execute marketable customer orders fully and promptly. However, that obligation does not create unlimited liquidity or guarantee that the entire quantity will execute instantly under every market condition. FINRA Rule 5310: Best Execution and Interpositioning

A meaningful review should examine:

1. available executable liquidity;
2. order price and conditions;
3. routing;
4. timestamps;
5. competing orders;
6. session;
7. subsequent handling of the remaining quantity.

Professional analysis — Alexander Styopin: The most dangerous part of a partial fill is often not the missing execution. It is the trader’s response. A trader sees 500 of 1,200 shares completed, submits another order for the full 1,200, and forgets that 700 shares from the first order remain active. The market then returns to the original price and both orders execute. The correct reference point is always the live account state: confirmed position, cumulative fills, remaining quantity, and every active order.

A partial fill is a normal execution outcome when the market cannot immediately supply the full requested quantity under the order’s price and other conditions. The completed shares are real transactions. The balance must be evaluated separately.

Before changing the order, determine whether the balance is still working, pending cancellation, expired, or already canceled. If a replacement is needed, calculate it from the confirmed current position and wait for the original cancellation status whenever possible.

Alexander Styopin is a hi2morrow analyst and an economist with 25 years of experience in the US stock market.

Reviewer status: Subject-matter review is required before publication.

Editorial note: New article researched and verified on August 10, 2026. Broker status labels, cancellation workflows, time-in-force availability, extended-hours rules, linked-order handling, and queue treatment must be rechecked before publication.

Educational material only. Not investment advice. Order routing, partial executions, cancellations, replacements, priority, session eligibility, and status reporting can vary by broker, venue, security, account, and market condition.

Sources

1. Investor.gov: Executing an Order
2. Investor.gov: Understanding Order Types
3. Investor.gov: Fill-or-Kill Order
4. FINRA Rule 5310: Best Execution and Interpositioning
5. FINRA: Time Parameters and Qualifiers on Stock Orders
6. Nasdaq Trader: FIX Interface Specification
7. Fidelity: Orders Help
8. Fidelity: Trading FAQs—Order Types
9. Fidelity: Trading FAQs—Placing Orders
10. Fidelity: Extended-Hours Order Handling
11. Charles Schwab: Stock Order Types and Conditions
12. Interactive Brokers: One-Cancels-All Orders

Author: Alexander Styopin, hi2morrow analyst and economist with 25 years of experience in the US stock market

Originally published: August 10, 2026