Immediate-or-Cancel: Fill Now, Drop the Rest

Key Takeaways

• An immediate or cancel order IOC fills what it can instantly and cancels the unfilled remainder.
• It allows partial fills, which is the key difference from a fill-or-kill order.
• It never rests in the order book, so it leaves no standing exposure.
• Traders use IOC to take available liquidity without revealing a resting order.

What an Immediate or Cancel Order IOC Is

An immediate or cancel order IOC is a time-in-force instruction. Time in force controls how long an order stays live, and IOC sets that window to a single instant. FINRA describes it as an instruction to "fill as much of your order as possible right away," with any portion that cannot execute immediately canceled.

The defining feature is that an IOC accepts a partial fill. If only some of your size can trade at once, you take that amount and the rest is dropped. Nothing is left working in the market.

The Intuition

Sometimes you want to grab whatever liquidity is on offer this second without leaving a resting order behind. A standard limit order that does not fill stays in the book, visible to others and exposed to later price moves. An IOC avoids that. It reaches into the market, takes what it can, and disappears.

This suits traders who want to act on the liquidity they can see right now and would rather get a partial fill than wait. It also keeps their full intended size hidden, since the order never rests where others can read it.

How It Works

An IOC is attached to a limit or market order and executed against whatever interest is immediately available at an acceptable price. Any unfilled quantity is canceled at once.

IOC: fill immediately, allow partial fill, cancel the remainder
FOK: fill the entire order immediately, or cancel all of it

The contrast with fill or kill matters. FINRA notes that an FOK order executes "your entire order immediately or not at all," with no partial fills. An IOC is more flexible: it takes a partial fill where FOK would cancel everything. So IOC sits between an ordinary limit order, which can rest and wait, and FOK, which demands all-or-nothing right now. Because an IOC never rests, the price you set acts as a ceiling for a buy or a floor for a sell on whatever fills instantly.

Worked Example

A trader wants to buy 5,000 shares but only at 30.00 or better, and does not want to leave a resting order that others can see.

The trader sends a buy immediate or cancel order IOC for 5,000 shares with a limit of 30.00. At that moment the order book shows 3,000 shares offered at 30.00 and the next block at 30.05. The IOC fills 3,000 shares at 30.00 immediately, then cancels the remaining 2,000 because they cannot fill at 30.00 or better right now. The trader ends with 3,000 shares and no resting order.

Compare this with a fill-or-kill order for the same 5,000 shares at 30.00. Because the full 5,000 could not fill instantly, FOK would have canceled the entire order and the trader would own nothing. The IOC captured the available liquidity; FOK demanded all or none. Which is better depends on whether a partial position is useful or a nuisance.

Common Mistakes

1. Expecting a full fill. An IOC takes only what is available instantly. Planning around a complete fill leads to surprise partials.
2. Confusing IOC with fill or kill. IOC allows partial fills; FOK does not. Choosing the wrong one changes whether you get a partial position or nothing.
3. Using IOC when you want to wait. If you are happy to rest in the book until your price arrives, a day or GTC order fits better. An IOC gives up that patience.
4. Sending many IOCs into a thin market. Repeatedly probing for liquidity can leave you with scattered small fills and added cost.
5. Forgetting the price limit still applies. An IOC limit order will not fill above your buy limit or below your sell limit, so a poorly set limit can return zero shares.

Frequently Asked Questions

What is an immediate or cancel order IOC in simple terms? An immediate or cancel order IOC fills as much as it can right now and cancels whatever is left over. It accepts a partial fill rather than waiting.

How does an immediate or cancel order IOC affect investment decisions? It lets you take available liquidity instantly without leaving a resting order exposed. In the worked example, an IOC bought 3,000 of 5,000 shares at the limit and canceled the rest immediately.

What is a real-world example of an immediate or cancel order IOC? A trader wanting 5,000 shares at 30.00 sends an IOC, fills the 3,000 shares offered at that price, and the remaining 2,000 are canceled at once.

How can investors use an immediate or cancel order IOC effectively? Use it to capture visible liquidity without resting in the book, set a sensible limit price, and accept that you may receive only a partial fill.

How is an immediate or cancel order IOC different from a good till canceled order? An IOC acts instantly and cancels the unfilled portion immediately. A GTC does the opposite, resting in the market across days until it fills or you cancel it.

Sources

1. FINRA. Trading Terms: Time Parameters and Qualifiers on Stock Orders. https://www.finra.org/investors/insights/time-parameters-qualifiers-stock-orders
2. FINRA. Order Types. https://www.finra.org/investors/investing/investment-products/stocks/order-types
3. SEC Investor.gov. Types of Orders. https://www.investor.gov/introduction-investing/investing-basics/how-stock-markets-work/types-orders
4. SEC Office of Investor Education and Advocacy. Trading Basics. https://www.sec.gov/files/trading101basics.pdf

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.