# Day order

Day order is an order instruction that keeps an unfilled stock order active only for the applicable trading day, after which the broker cancels any remaining quantity.

## What it means

A day order sets a time limit on an order, not a price limit. Its **time in force** is the applicable trading day: any quantity still open when that period ends is canceled. It does not automatically carry forward to the next trading day.

A day order can be a market order or a limit order. A market order generally seeks an immediate execution, but its day designation still does not guarantee a fill. A day limit order may remain open while the market is trading if its price condition is not met. Either type can fill completely, fill partly, or remain unfilled.

The exact cutoff depends on the broker, market, and whether the order is eligible for extended-hours trading. A broker may also apply its own rules to orders submitted after the regular session closes. Check the order ticket and broker terms for the applicable expiration time.

## How it is calculated

A day order has no pricing formula: “day” describes duration. For an order that can receive partial fills, its unfilled quantity is calculated as `Q_remaining = Q_ordered − Q_filled`, where `Q_ordered` is the number of shares submitted, `Q_filled` is the number executed during the order’s active period, and `Q_remaining` is the number of shares left open. Each variable is measured in shares. At the applicable cutoff, the broker cancels the remaining quantity; already executed shares stay executed.

This quantity calculation does not determine whether an order will fill or what price it will receive. Those outcomes depend on the order type, available liquidity, market conditions, and the broker’s execution arrangements.

## Worked example

Suppose, hypothetically, an investor submits a day limit order to buy 100 shares at no more than US$20 per share during the regular trading session.

1. The order starts with `Q_ordered = 100 shares` and `Q_filled = 0 shares`.
2. Before the applicable cutoff, 40 shares execute at US$20 each. The executed purchase is `40 × US$20 = US$800`, excluding fees.
3. The unfilled quantity is `100 − 40 = 60 shares`.
4. If no more shares execute before the cutoff, the broker cancels those 60 shares. The 40-share fill remains a completed transaction; the canceled 60 shares do not become an order for tomorrow.

The limit price capped the price per share for this hypothetical buy order; the day designation determined how long the order could remain active. Neither condition guaranteed that all 100 shares would execute.

## Why it matters before you trade

The expiration choice affects whether an unfilled order can remain available for execution after today. That matters when prices move, news arrives, or the investor’s intended position size changes. A day order avoids leaving its unfilled quantity active on later trading days, but it may require a new order if the investor still wants the remaining shares.

Check the side, quantity, order type, limit price if applicable, trading session, and time in force before submitting an order. If a partial fill occurs, distinguish the shares already executed from those canceled. Also account for any fees and the actual fill prices when assessing the completed portion.

## How PreTrAIde uses it

PreTrAIde is pre-trade analysis software, not a broker. A user builds a stock basket with a side, quantity, and execution conditions for each line. PreTrAIde analyzes the basket before an order is placed and returns a GO, NO-GO, or MODIFY verdict, risk assessment, and suggested execution strategy with plain-language reasoning.

The product facts do not specify that PreTrAIde sets, submits, or monitors day orders. Its pre-trade check can inform consideration of execution conditions, but the user chooses and places any order through their own broker. A PreTrAIde verdict is decision support, not an instruction to trade or a guarantee of execution.

## Common mistakes

- **Confusing duration with price protection.** “Day” says when an order expires; a limit price, if present, sets a price boundary.
- **Assuming the entire order must fill or cancel.** A day order can fill partly, leaving only the unfilled balance to expire.
- **Assuming every broker uses the same cutoff.** Regular-session and extended-hours rules can differ; verify the applicable time on the order ticket.
- **Treating cancellation as a reversal.** Expiration cancels only unfilled shares. It does not undo shares already bought or sold.
- **Assuming an order placed near the close lasts 24 hours.** Its active period depends on the broker’s applicable trading-day rules, not a rolling 24-hour clock.

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Source: https://pretraide.com/glossary/day-order