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Key Takeaways
- Fill-or-kill requires the entire order quantity to execute immediately under its price and routing terms.
- An immediate-or-cancel order permits a partial fill; FOK requires full completion.
- Count the eligible quantity through the limit price when evaluating the order.
- The worked 1,000-share request has 950 eligible shares, so the whole order cancels.
- For a multi-leg options trade, send the whole package as one complex FOK so every leg fills together or none does.
What is a fill-or-kill order?
A fill-or-kill order, or FOK, is an order that requires immediate execution of the full quantity under its price and routing terms. If the complete quantity is unavailable at evaluation, the order cancels with zero execution. FOK combines immediacy with full completion.
Formula
FOK condition = immediately executable eligible quantity ≥ order quantity- Eligible quantity must satisfy the order price and any routing, venue, or counterparty constraints.
- If the condition is false at evaluation, the entire order is canceled.
Fill-or-kill order example: counting eligible depth
A trader submits a fill-or-kill limit order to buy 1,000 shares at $25.05. Eligible offers contain 300 shares at $25.02, 450 at $25.04, and 200 at $25.05.
- Eligible quantity: 300 + 450 + 200 = 950 shares
- Requested quantity: 1,000 shares
- Shortfall: 1,000 − 950 = 50 shares
Because only 950 eligible shares are immediately available, the FOK condition fails. The venue cancels all 1,000 shares and reports no partial execution.
The worked buy requests 1,000 shares with a $25.05 limit. It can use 300 shares at $25.02, 450 at $25.04 and 200 at $25.05. The total is 950, leaving a 50-share shortfall. The FOK therefore executes zero shares.
For a second depth example, 500 shares at $20.08 and 700 at $20.10 supply 1,200 eligible shares for a $20.10 buy limit. A supported 1,000-share FOK can consume 500 at each price, averaging $20.09. A 1,300-share FOK cancels.
FOK vs IOC and all-or-none orders
An immediate-or-cancel order accepts a partial fill and cancels the rest. An all-or-none instruction controls quantity while its separate time-in-force governs how long it stays active. FOK requires both conditions at once: the full quantity, immediately.
How to set quantity, limit and route on a FOK order
The limit sets the worst acceptable price, and the route sets where the order can trade. The FOK instruction adds the all-at-once test: the full quantity at evaluation, or nothing.
Use an order type your broker supports for that venue, product and session. For multi-leg options, a native complex FOK controls the package ratio and net price. Separate single-leg FOK orders apply independently.
Check the execution report before you resubmit. It shows whether the order filled in full or canceled, and at what prices. For a multi-leg trade, a structure priced in the options profit calculator supplies the complete package and net limit for the broker’s order ticket.
Limitations of fill-or-kill orders
- Check the eligible depth before you submit. An order that cannot complete executes nothing: the worked request is 50 shares short of 1,000 and fills zero, so the trader must decide whether to resubmit.
- Submit when the depth is there. The condition is checked once, at evaluation, and liquidity that arrives a moment later does not count toward the order.
- Count only eligible depth. Route, venue and counterparty constraints limit the shares that count, so displayed depth can overstate it.
- Confirm that your broker accepts FOK for the venue, product and session before you rely on it.
- Send a multi-leg trade as one native complex FOK. Separate single-leg FOK orders apply independently, so one leg can fill while another cancels.
Bottom line
A fill-or-kill order executes the whole quantity right away at acceptable prices, or nothing at all. Use it when a partial fill would leave an unwanted position, count the eligible depth through your limit before submitting, and use a native complex instruction for multi-leg options.
Clear answers
Frequently Asked Questions
Sources and Further Reading
- Cboe: Titanium U.S. Equities BOE Specification
- NYSE: Pillar Equities FIX Gateway Specification
- Nasdaq: NOM and BX Options FIX Specification
How entries are sourced, calculated and updated: editorial methodology.