What is a fill-or-kill (FOK) order?
In one line: A fill-or-kill order must be filled completely and right away. If the full amount can't be filled at once, the whole order is canceled.
How it works
"Fill or kill" is a Time in force setting with two strict rules.
- All of it. No part fills. It's the full size or nothing.
- Right now. It doesn't wait. If the size isn't there this instant, it's gone.
It's usually paired with a Limit order, so there's also a worst price you'll accept.
A simple example
You want to buy 500 shares at $20.00 or better. You send it as fill or kill.
Look at the sellers waiting in the Order book:
| Price | Shares offered |
|---|---|
| $19.98 | 200 |
| $20.00 | 100 |
| $20.02 | 400 |
At $20.00 or better, only 300 shares are for sale. That's short of 500. So the order is killed. You buy nothing, and the order disappears.
If 500 shares had been there, all 500 would fill at once.
Why it exists
Some traders need a set size or none at all. Maybe their plan only works with the full amount. Maybe they don't want a small leftover position to manage. Fill or kill stops a Partial fill from ever happening.
It's used more by large traders and algorithms than by beginners. Many retail stock platforms don't even offer it on every order. Crypto exchanges often do.
How it compares with IOC
| Fill or kill | Immediate or cancel | |
|---|---|---|
| Waits? | No | No |
| Partial fill allowed? | No | Yes |
| Result in the example | 0 shares | 300 shares, 200 canceled |
A common mistake
Using it on a thin market and thinking the platform is broken. If the order keeps getting canceled, the size you asked for just isn't there at your price. Smaller size, a different time of day, or a plain limit order that can wait may suit you better.
Questions
What does FOK mean in trading?
FOK stands for fill or kill. The order fills in full right away, or it's canceled.
Is fill or kill the same as all or none?
Close, but not the same. An all-or-none order must also fill in full, but it can wait. Fill or kill can't wait: it's now or never.
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