Time in Force

Time in force controls how long an order stays active and how it handles partial fills.

A GTC order rests in the book until it is fully filled, manually cancelled, or the exchange session ends. GTC is the default time in force for limit orders and is appropriate for the vast majority of trading use cases.

When a GTC order is partially matched — for example, only 0.5 ETH of a 1 ETH order is filled — the remaining 0.5 ETH stays in the book at the original price, waiting for additional counterparty flow.

An IOC order attempts to fill as much as possible immediately. Any quantity that cannot be matched immediately is cancelled — it never rests in the book. IOC is useful when you want to take available liquidity at a price but are not willing to wait for the remainder.

Example: you submit a limit IOC buy for 2 ETH at $3,200. The best ask has 1.5 ETH available at $3,199. The order fills 1.5 ETH immediately. The remaining 0.5 ETH is cancelled. Your resulting fill is 1.5 ETH at $3,199.

A FOK order must be fully filled immediately or it is cancelled entirely. No partial fills are permitted. If the book cannot accommodate the full quantity at the limit price at the moment the order arrives, the entire order is rejected.

FOK is used when a partial fill would be operationally problematic — for example, a hedging strategy that requires exact position sizes. It is the most restrictive time in force.

A Post-Only order is accepted only if it would rest in the book as a maker order — that is, if it would not immediately match any existing resting order. If the order would cross the spread and take liquidity, it is rejected outright.

Post-Only is used by market makers who want to guarantee they receive the maker rebate rather than paying the taker fee. If market conditions shift and your quote would cross the spread before you can cancel it, Post-Only prevents you from accidentally taking liquidity.