Immediate or Cancel Order: How IOC Orders Work in Trading

An immediate or cancel order is an instruction to buy or sell a security right away, filling as many shares as the market can provide at that moment. Whatever cannot be filled immediately is automatically canceled. Nothing stays open on the order book, which is the defining feature of an IOC order.

This page is for investors and active traders who already know the basics of market and limit orders and want to control how long an order stays alive. If that is you, read the mechanics, compare IOC with the other time-in-force options in the table below, then check whether your broker supports IOC before you need it. This article is educational, not financial advice.

What an immediate or cancel order is

Every order you send to a broker carries two decisions: the price terms (market or limit) and the time terms, known as time in force. The immediate or cancel instruction is a time-in-force option. The SEC's investor glossary defines an IOC order as one that must be executed immediately, with any unfilled portion canceled rather than left working.

Two things make IOC distinct. First, it accepts partial fills: if only some shares are available, you get those shares. Second, it never lingers. There is no open order sitting in the market that could execute minutes or hours later at a price you no longer want.

How an IOC order works step by step

The lifecycle is short by design:

1. You submit the order, usually as an IOC limit order with a price cap or floor.
2. The exchange or trading venue matches it against available shares at your price or better.
3. Any filled portion executes instantly.
4. The unfilled remainder is canceled automatically, with no further action from you.

Here is a worked example. Say you place an IOC limit order to buy 1,000 shares at $50.00, and only 600 shares are offered at $50.00 or less at that instant. You buy the 600 shares. The remaining 400 shares are canceled immediately instead of waiting on the book. Your account now shows a 600-share position and no open orders.

Compare that with a plain day limit order for the same 1,000 shares: the leftover 400 would sit open for the rest of the session and could fill later, possibly after news has changed your view of the stock.

IOC vs FOK, GTC, and other time-in-force options

FINRA's guide to time parameters groups the common time-in-force choices. The table below compresses the differences:

The IOC vs FOK distinction matters most. Both demand immediate execution, but FOK cancels the entire order if it cannot fill completely, while IOC takes whatever is available. Per FINRA's descriptions, IOC behaves like "take what you can get now," while FOK is all or nothing. GTC sits at the other extreme: your broker keeps working the order, sometimes for months, until it fills or you cancel it.

When traders use IOC orders

IOC fits situations where leftover open orders create more risk than missed shares:

• Fast-moving markets. When prices are changing quickly, a resting order can fill at a moment you did not choose. IOC removes that exposure by living for only an instant.
• Large orders in liquid stocks. A trader working a big position can send repeated IOC slices, capturing the liquidity available at each price level without signaling a large resting order to the market.
• Pairing trades. If a stock purchase only makes sense alongside another position, such as an options trade, an IOC order avoids ending up with a stale fill after the window has passed.
• Avoiding order-management overhead. Anything unfilled cancels itself, so there is nothing to remember to cancel at the end of the day.

A realistic scenario: a stock you follow drops sharply on an earnings headline. You want up to 500 shares, but only at $42.00 or better, and only right now, while the dislocation lasts. An IOC limit order at $42.00 buys whatever is available at that price this second and cancels the rest, sparing you an open order that might fill after the price recovers.