PriceLimit — you name the worst price you will acceptMarket — walks the book, bounded by a protective limit
Time in forceGTC rests · IOC cancels the remainderFOK is all or nothing · post-only is rejected if it would take
FlagsReduce-only — the order may only shrink a positionIt can never open one, and never reverse you
Your order
The three are independent: any price with any time in force, with or without the flag.
Limit or market
A limit order names the worst price you will accept. A buy fills at your price or better; a sell at your price or better. You control the price exactly and take no slippage — in exchange for no guarantee of filling at all. If the market never reaches your price, the order simply waits. A limit order that does not cross the book rests on it, making you a maker and earning the maker fee, which is lower than the taker fee. See Fees. A market order prioritizes execution over price. It walks the opposing side of the book from the touch inward until your size is filled. What actually reaches the matching engine is not an unbounded market order. It is converted into a limit order with a protective price bound derived from your slippage tolerance, the market’s price band, and the depth your size would consume. This is why a market order can come back partially filled — the bound was reached. See Market orders and slippage protection.Time in force
Time in force answers one question: what happens to the part of my order that does not fill right now?
Only one applies per order.
GTC — good till cancelled — is the default for resting orders. Not literally forever: orders carry a maximum lifetime so that the book does not accumulate abandoned orders indefinitely.
IOC takes what the book offers at your price and cancels the rest. A buy for 15 against 10 available fills 10 and cancels 5.
FOK is all or nothing. The same order fills 0 — because 15 is not available, nothing executes. Use it when a partial position is worse than no position: legging into a spread, or any strategy where half a fill leaves you exposed rather than positioned.
Post-only guarantees maker status. If the order would cross and take liquidity, it is rejected rather than executed. This is how market makers ensure they never accidentally pay the taker fee.
Flags
Reduce-only guarantees the order can only shrink a position, never open or flip one. It is checked at submission and re-enforced as your position changes, and it reserves no margin. See Reduce-only.Conditional orders
Everything above describes orders that are live the moment they are accepted. A conditional order is different: it rests off the book watching a price, and only becomes one of the orders above when its trigger fires. That includes take-profit and stop-loss, which are conditional orders scoped to protect something you already hold. See Conditional orders and Take-profit and stop-loss.Choosing
The most common expensive mistake is a market order that is large relative to visible depth. The touch price is what you see; the average fill price is what you get, and the difference grows with your size. Check the depth before submitting, or split the order.
Where to go next
Conditional orders
Orders that wait for a price before becoming live.
Market orders
How the protective bound on a market order is derived.
Order book
Reading depth before deciding how to submit.
Modify orders
Changing a live order, and what it costs in queue position.