Who this is for — Anyone entering limit orders close to the market who wants to control their initial interaction with the book. Post-only expresses an intention not to remove liquidity immediately; it is not a universal promise about the economic outcome.
Post-only is an instruction normally attached to a limit order. It asks a trading venue to accept the order only under that venue's rules for passive liquidity, rather than handling it as an order that immediately crosses the book.
It is not a synonym for limit order. A limit can be marketable: a buy limit at or above the best ask may execute immediately, and a sell limit at or below the best bid may do the same. Post-only changes how the venue handles that situation.
Maker and taker describe the interaction
Under a maker-taker model, an order that rests in the book adds available liquidity; one that immediately matches an existing order removes it. These roles refer to an execution and the venue's rules, not to a permanent identity of the trader.
| Incoming order | Without post-only | With post-only |
|---|---|---|
| non-marketable | may be accepted and queued | can normally be queued |
| marketable | may execute immediately as the aggressor | the venue-specific logic applies |
| invalid or unavailable in the current market state | may be rejected | may be rejected |
“Maker or canceled” describes some implementations, but not all. The rulebook may provide for rejection, cancellation, repricing or another outcome.
Four documented outcomes
Official sources show why the result cannot be inferred from the name of the instruction alone.
| Outcome | Example of a documented rule |
|---|---|
| Rejection | Coinbase Exchange rejects the entire order if any part would remove liquidity |
| Cancellation | Coinbase Derivatives and OKX describe cancellation of an immediately executable order |
| Repricing | Nasdaq may slide the price of an order that would lock a quote, or cancel it, according to the port setting |
| Execution | the 2026 Nasdaq fact sheet describes cases where post-only logic does not apply and the order is processed as IOC at the best price |
Nasdaq also documents different treatment for displayed, non-displayed, midpoint and protected quotes at other market centers. The entry protocol and participant settings may alter the outcome. This is a Nasdaq-specific rule, not a general definition that can be transferred to crypto-asset exchanges or other securities markets.
Example: the book changes in transit
Assume a best bid of 100.00 and a best ask of 100.02. A post-only buy limit is sent at 100.01. Before it reaches the matching engine, the ask falls to 100.01.
The platform may:
- reject the new order;
- accept and immediately cancel it;
- reprice it to an allowed passive level;
- apply a special rule that permits execution.
Repricing still does not guarantee a fill: the new price may be away from the market, and queue position depends on the priority rules. See Order priority and partial fills.
It does not guarantee a fee, rebate or fill
Post-only does not guarantee a particular fee. Cost depends on the venue's fee schedule, the customer's pricing tier, the instrument, the type of session and the classification assigned to the fill. A venue may charge a maker fee, charge no fee or pay a rebate, and those terms may change.
It also does not guarantee:
- acceptance of the order;
- persistence at the submitted price;
- initial priority or retained priority after repricing;
- a complete or partial execution;
- a better price than an aggressive order;
- freedom from opportunity cost while the market moves away.
The value of a lower fee may be smaller than the price lost or the cost of non-execution. The proper comparison belongs in transaction costs and execution quality, not in the maker label alone.
Relationship with time in force and market state
Post-only and time in force answer different questions:
post-only = how may the order interact on arrival?
time in force = how long is it valid and what happens to the remainder?
The instructions cannot always be combined. Coinbase Exchange, for example, documents post-only as incompatible with IOC and FOK. Auctions, limit-only, post-only or cancel-only modes, trading halts and price controls can also change which orders are accepted.
A broker may not transmit the flag with the same meaning displayed in its interface, may choose a different venue or may impose its own controls. For a routed order, the broker's policy must be distinguished from the rulebook of the final venue.
Venue and broker dependence
Before using the instruction, verify the applicable documentation for:
- supported order types and TIF combinations;
- whether a marketable order is rejected, canceled or repriced;
- whether any exception permits execution;
- how priority changes after a price slide or modification;
- returned status and reason codes;
- the fee applied to the actual fill;
- behavior in an auction or special market mode.
Useful logs retain the submitted price, observed best bid and ask, timestamp, price accepted by the venue, final status, fills and actual fee. Without those data, it is not possible to determine whether post-only prevented aggressive execution or merely produced a missed order.
Sources
- Nasdaq Trader — Post-Only Order Fact Sheet, 2026
- Coinbase Exchange — Create a New Order
- Coinbase Derivatives Exchange — Supported Order Qualifiers
- OKX — Basic Order Types