An immediate-or-cancel order, usually shortened to IOC, tells the exchange to fill as much of your order as it can right now at your price and cancel whatever isn’t filled the instant it finishes checking. Nothing rests on the book. You either walk away with some shares, all of them, or none, and you know which within a fraction of a second.
How the Order Behaves Once It Hits the Exchange
You send the order, the matching engine sweeps the book for shares available at your limit price or better, fills what it can, and immediately cancels the rest. There’s no queue and no waiting period. Nasdaq’s rulebook defines IOC as an order “designated to deactivate immediately after determining whether the Order is marketable.”1Nasdaq. Nasdaq Equity 4 The whole cycle happens automatically.
One point that trips people up: IOC isn’t only for limit orders. Nasdaq’s glossary defines the instruction as covering a “market or limited price order.”2Nasdaq. Immediate or Canceled Order (IOC Order) A market IOC takes whatever price is available; a limit IOC only trades at your price or better. Most traders pair IOC with a limit, because a market IOC on a thinly traded stock can fill at a price you’d rather not see.
Partial Fills Are the Point
The willingness to take a partial fill is what separates IOC from stricter instructions. Send an IOC for 1,500 shares, find only 700 available at your price, and you get the 700. The other 800 cancel. Charles Schwab puts it plainly: IOC orders “require that any part of an order that can be filled immediately is filled, and any remaining shares are cancelled.”3Charles Schwab. Stock Order Types and Conditions: An Overview
The canceled portion doesn’t carry over. It’s gone. Your account shows the shares filled and a cancellation notice for the balance. If the liquidity you swept sat at several price levels within your limit, the fill may report as multiple smaller executions rather than one clean print. That’s normal, not a duplicate order.
On the NYSE’s Pillar platform, IOC orders that don’t route to other venues support an optional minimum quantity, which must be at least one round lot (typically 100 shares). Without it, the exchange will fill odd lots too, so you could end up with 37 shares if that’s all that was available at your price.4NYSE. Pillar Differences – Order Type Differences The minimum quantity setting lets you avoid tiny fills that aren’t worth the trouble.
IOC vs. Fill-or-Kill vs. All-or-None
Three instructions demand fast execution, and they sound alike but behave very differently. Picking the wrong one can mean getting nothing when a partial fill would have suited you fine.
- Immediate-or-cancel (IOC). Fill what you can right now, cancel the rest. Partial fills are allowed. Never rests on the book.
- Fill-or-kill (FOK). Fill the entire quantity right now or cancel the whole thing. No partial fills. Also never rests on the book. IOC and FOK both refuse to sit; only FOK also refuses to fill in pieces.
- All-or-none (AON). Fill the entire quantity or nothing, but the order can stay active for the rest of the trading day. AON also requires execution at a single venue, which can block fills that would have worked if the order were split across exchanges.3Charles Schwab. Stock Order Types and Conditions: An Overview
The practical read: IOC gives you the best odds of getting at least some shares immediately. FOK is for situations where a partial fill is useless, like hedging a specific options position where 700 shares out of 1,500 leaves you exposed. AON is less common in fast markets because it can linger, but it prevents an awkwardly small position.
Placing an IOC Order
Placing one works like placing any other order, with one setting most people miss. You need the ticker, the share count, your limit price (if using a limit), and the time-in-force set to IOC rather than the default “Day.”
Before choosing your limit, look at the current bid-ask spread. An IOC set far from the inside market will almost always cancel entirely, because there are no resting orders to match against out there. Setting it at or near the current ask (for a buy) or bid (for a sell) gives the order a real chance. For thinly traded stocks, the spread can be wide enough that a mid-spread limit finds nothing to fill.
Most platforms bury the time-in-force option in a dropdown that defaults to “Day.” Change it to IOC before you submit. Review the summary screen, verify the ticker, share count, limit price, and estimated cost including commission, then send.
Confirmation is nearly instant. Your order status will show one of three outcomes: fully executed, partially executed with the remainder canceled, or fully canceled. On a partial fill, the ledger tells you exactly how many shares filled and at what price, and you can decide whether to send a new order for the balance.
Extended Hours
IOC instructions work outside regular trading hours too. Both Nasdaq and NYSE Arca accept them in pre-market and post-market sessions, subject to some session-specific handling. Liquidity in these sessions is thinner and spreads are wider, which means the odds of a full cancellation are higher than during the core session. Your broker is required to disclose the material risks of extended-hours trading before accepting an order for those windows.5U.S. Securities and Exchange Commission. NYSE Arca Rule Filing Exhibit 5 – Rule 7.34-E(T)
When to Use It, When Not To
IOC earns its place when leaving a resting order on the book is riskier than walking away empty-handed. A few situations where the instruction fits:
- Sweeping visible liquidity. You see shares at a price you like and want them before the quote moves. IOC takes what’s there and leaves nothing behind to signal your interest.
- Reducing information leakage. A resting limit tells the market you’re a buyer or seller at a specific price. Institutions in particular use IOC to avoid tipping off other participants when building or unwinding a position through many smaller orders.
- Fast-moving markets. A day order placed at 10:02 a.m. might still be sitting at 10:15 a.m. at a price that no longer makes sense. IOC eliminates stale-order risk.
- Capital management. If a fixed amount of capital is earmarked for a trade, IOC frees the unfilled portion immediately instead of tying up your buying power.
IOC is a poor fit when you’re willing to wait for a better price, when the stock is so thinly traded that no immediate liquidity exists at any reasonable level, or when you truly need the entire quantity. For that last case, fill-or-kill prevents the partial position that IOC will hand you without hesitation.
One cost note worth keeping in mind: partial fills can generate multiple trade reports. If your broker charges per execution rather than per order, an IOC that fills in four pieces could produce four commissions on what you intended as a single trade. Check the fee schedule before leaning on IOC as a routine tool.