An Immediate or Cancel (IOC) order instructs a broker or exchange to fill as much of the order as possible at the specified price right now, then automatically cancel any remaining unfilled quantity. Unlike a Day limit order that sits passively in the order book or a market order that sweeps through every available price level, an IOC is a single, non-resting attempt to transact — making it the preferred execution tool for traders who need speed without exposure.
Key Takeaways
- IOC accepts partial fills: if only 250 of your 400 requested shares are available at the limit price, you receive 250 and the remaining 150 are cancelled — never placed into the book.
- IOC eliminates order book visibility risk. Because the order never rests, market makers and other participants cannot see or react to your resting interest.
- Partial fills require immediate position sizing recalculation — your original stop-loss dollar risk applies to fewer shares than planned.
How an IOC Order Works
When a trader submits an IOC order, the exchange’s matching engine checks available liquidity at the specified price in that exact moment. Whatever quantity is available gets filled; the remainder is discarded. The entire sequence happens within a single matching cycle — there is no waiting, no queuing, and no resting order.
On NYSE and NASDAQ, IOC orders are explicitly marked as non-displayed. They expire in the same matching cycle they are submitted, which means they contribute zero queue position and leave no visible footprint in the Level 2 order book.
IOC vs. related order types:
| Order Type | Partial Fill Allowed | Rests in Book | Cancels Remaining |
|---|---|---|---|
| IOC | Yes | No | Immediately |
| Fill or Kill (FOK) | No | No | Immediately |
| Day Limit | Yes | Yes | At market close |
| GTC Limit | Yes | Yes | Until cancelled |
The critical distinction from a Fill or Kill order: FOK requires 100% of the requested quantity to be available or it cancels entirely. IOC is more flexible — any partial fill is accepted. This makes IOC the better choice when trading larger size relative to average daily volume, where a full fill is unlikely but a partial position is still useful.
IOC is also the dominant time-in-force in dark pools and Alternative Trading Systems (ATS). Institutional desks use IOC orders to probe for hidden liquidity without telegraphing their full order size to the lit market.
Practical Example
A scalper is trading AAPL during an earnings gap-up. The trader wants to buy 400 shares at a limit order price of $198.50. The order book shows only 250 shares offered at $198.50, with the next available 200 shares sitting at $198.75.
With an IOC order submitted at $198.50:
- The matching engine finds 250 shares available at $198.50.
- Those 250 shares fill immediately at $198.50.
- The remaining 150-share order is cancelled — it never appears in the book at $198.50.
- No resting limit is visible to market makers.
The trader is now long 250 shares instead of the planned 400. The original plan was to risk $250 (1% of a $25,000 account) with a $1.00 stop. With 250 shares and a stop at $197.50, the risk is still exactly $250 (250 shares × $1.00). The position sizing math still works.
Had the trader used a FOK order, the entire 400-share order would have cancelled because the full quantity was not available at $198.50 — leaving the trader flat during the gap-up move.
An Immediate or Cancel order fills as much of your trade as possible at your specified price right now, then cancels whatever is left unfilled. It never sits in the order book, so other traders cannot see your resting interest. Partial fills are accepted.
Common Mistakes
- Ignoring partial fill risk before entry. Traders who plan their full stop-loss around 500 shares and receive only 200 often leave their stop at the original dollar amount — creating outsized risk per share. Recalculate stop distance immediately after a partial IOC fill.
- Using IOC in illiquid instruments without checking the spread. In thinly traded small-caps or pre-market sessions, an IOC limit order may return zero shares if the spread is wide and no seller is at your exact price. A market order may be more reliable when fill certainty matters more than price precision.
- Confusing IOC with FOK on platform order tickets. On some platforms the TIF dropdown lists both. Selecting FOK when you need a partial fill means the order may cancel entirely — confirm the label before submitting during fast-moving conditions.
- Sending multiple IOC orders in rapid succession. Stacking IOC orders to “chase” a moving price compounds slippage. If the first IOC doesn’t fill at your target, reassess whether the entry thesis still holds before resubmitting at a higher limit.
How JournalPlus Tracks IOC Orders
JournalPlus automatically imports execution data including time-in-force and fill details from connected brokers, so partial IOC fills are logged as distinct entries with actual fill quantity and price. The trade journal surfaces partial fill frequency over time, letting traders measure how often their IOC entries result in undersized positions and whether those positions underperform versus full-fill trades.
