What is the "Post Only" option when placing an order on Binance?

Definition and Core Functionality

1. The 'Post Only' option is a conditional order type available on Binance’s spot and futures trading interfaces.

2. When enabled, the order will only be placed if it does not immediately match with an existing order on the opposite side of the order book.

3. If the order would execute against resting liquidity — meaning it would act as a taker — the system rejects it outright instead of filling it.

4. This mechanism ensures the order remains strictly on the order book as a maker, preserving the maker fee discount.

5. It functions independently of price slippage or market volatility — its behavior depends solely on whether the order crosses the spread at submission.

Fee Implications and Economic Incentives

1. Binance applies tiered maker-taker fee structures where makers receive lower or even negative fees depending on 30-day trading volume and BNB holdings.

2. A 'Post Only' order guarantees eligibility for maker rates, provided it successfully posts to the book without triggering immediate execution.

3. Orders submitted with this flag that fail to post due to crossing the spread incur no fee — they are simply canceled without charge.

4. Traders leveraging high-frequency strategies or liquidity provision models rely on this flag to avoid unintended taker fees during rapid market movements.

5. Arbitrageurs use it to maintain clean order book positioning while avoiding adverse selection in fragmented liquidity environments.

Interaction with Order Types

1. 'Post Only' is compatible with limit orders exclusively — market, stop-market, and trailing stop orders do not support this flag.

2. When combined with time-in-force parameters like GTC or IOC, the 'Post Only' condition takes precedence over execution immediacy.

3. An IOC order with 'Post Only' enabled behaves paradoxically: it attempts to post, but if immediate matching occurs, it cancels rather than executes — effectively nullifying the IOC intent.

4. Trailing stop limit orders can include 'Post Only', but only after the trigger condition activates and converts into a limit order.

5. Conditional orders such as OCO (One-Cancels-the-Other) allow 'Post Only' on individual legs, enabling asymmetric risk management across entry and exit logic.

Risk Considerations and Behavioral Edge Cases

1. During extreme volatility, bid-ask spreads may widen rapidly; an order that initially qualifies as 'Post Only' might fail moments later due to microsecond-level book changes.

2. Latency-sensitive traders observe higher rejection rates when routing through API endpoints with elevated ping times relative to Binance’s matching engine.

3. Partial fills are impossible under 'Post Only': the entire order must post intact or cancel entirely — no hybrid maker-taker execution is permitted.

4. Some third-party charting tools misrepresent 'Post Only' rejections as failed API calls, leading developers to incorrectly attribute failures to authentication or rate limiting.

5. On futures markets, position size limits interact with 'Post Only' — an order may pass the post-check but still be rejected due to isolated margin constraints unrelated to liquidity alignment.

Common Questions and Direct Answers

Q: Does 'Post Only' prevent my order from being matched by stop-market or trailing stop orders?Yes. Stop-market and trailing stop orders execute as takers against resting liquidity. Since 'Post Only' orders never become takers, they cannot be filled by those triggers.

Q: Can I enable 'Post Only' on a reduce-only position order in Binance Futures?Yes. Reduce-only orders accept the 'Post Only' flag. The system evaluates both reduce-only compliance and post-only eligibility before placement.

Q: Why does my 'Post Only' limit buy at $25,000 fail when the best ask is $25,005?Because your order price is below the best ask, it qualifies as a maker. However, if another user places a market sell order milliseconds before yours arrives, the best ask may drop to $25,000 — causing your order to cross and get rejected.

Q: Is there a way to know in advance whether a 'Post Only' order will succeed?No real-time pre-validation endpoint exists. Success depends on live order book state at nanosecond-level precision — only the matching engine determines final outcome upon receipt.