Post-only order

Petr can buy with a Limit order that specifies his highest acceptable price. But if someone is already selling for less, an ordinary limit order can fill immediately. Kraken offers post limit for precisely the situation where Petr wants his offer to wait on the order book first. A later match would supply liquidity, an available offer for someone else. The price limit still matters; post-only adds another condition. [1]

Suppose Petr’s submitted order would immediately accept a waiting sell offer. Coinbase Exchange states that it rejects the entire post-only order, even if only part of the quantity could fill immediately. It does not split the order into an initial taker portion and a maker remainder. Preventing that immediate trade is the intended behaviour here. Petr therefore needs to establish whether his order is actually waiting or was never accepted. [2]

The label post-only does not predict the outcome on every platform. Coinbase Prime rules describe adjusting an immediately tradable price to the relevant best bid, meaning buy offer, or ask, meaning sell offer. That differs from rejection on Coinbase Exchange. Petr should identify the product he uses and read the actual accepted price in the confirmation. A similar service logo does not make all its interfaces follow the same rules. [3]

The price Petr saw while filling in the form need not hold when the order is processed. CFA Institute calls the delay between an event and a following action latency. Other participants can add offers, trade or withdraw offers in that interval. A limit that looked suitable for post-only a moment earlier may allow an immediate trade by the time it arrives. A snapshot of the book is neither a price reservation nor a promise of acceptance. [4]

Petr’s order is accepted, but that is not a ticket to the front of the queue. Coinbase Markets applies price-display-time priority; post-only does not itself change that sequence. Earlier eligible offers may therefore receive fills before Petr. His order can wait, fill in parts or never trade. Maker describes its role in a possible transaction, not an amount already purchased. [3]

Waiting on the book must be compatible with the other order rules. Coinbase Exchange, for example, does not allow post-only with IOC, which cancels any immediately unfilled remainder, or FOK, which requires an immediate complete fill. Kraken’s cited documentation does not offer post limit for Stop loss limit or Take profit limit, conditional limit orders intended to limit losses or take profits. Petr needs to check his product’s options and the market mode; instructions for another interface may not apply. [2] [1]

Kraken distinguishes post limit from reduce-only. The latter ensures an order only reduces an existing position rather than increasing it or opening a new one. Post-only does not replace that check or cancel an earlier order by itself. Coinbase Exchange also distinguishes acceptance, an open remainder and completion. If Petr changes his plan or buys another way, he must check the waiting order’s status separately. [1] [2]

People often use post-only to seek a maker rate. Kraken ties that rate to an actual fill; the label itself does not mean free trading. Waiting may also leave Petr without the intended purchase or paying a different price later. CFA includes delay and unfilled trades among trading costs. It therefore helps to compare the outcome of the whole intended transaction, not just the fee-rate difference. Post-only changes an order condition, not the uncertainty of the future market. [4] [1]