What is a post-only order and why do market makers use it?

Understanding Post-Only Orders in Cryptocurrency Trading

A post-only order is a type of limit order that ensures the trade will only be placed on the order book and never executed immediately as a taker. If the order would result in immediate execution against an existing order, it gets canceled instead of being processed. This mechanism allows traders to avoid paying taker fees, which are typically higher than maker fees.

Market makers rely heavily on post-only orders to maintain their position on the order book without triggering costly taker fees. By using this order type, they contribute liquidity rather than remove it, aligning perfectly with exchange incentive programs that reward liquidity provision.

How Post-Only Orders Function in Practice

1. When a trader submits a post-only limit order, the system checks whether it matches any existing orders on the opposite side of the book.
2. If there’s no immediate match, the order is added to the order book, classifying the trader as a maker.
3. In cases where the price overlaps with an active order, instead of executing, the system rejects or cancels the submission.
4. Some exchanges automatically adjust the price slightly to ensure the order remains non-marketable and stays on the book.
5. Traders can use this feature across various trading pairs and platforms, especially those offering tiered fee structures based on maker-taker models.

Why Market Makers Prefer Post-Only Orders

1. Fee minimization is a primary motivation—maker fees are often zero or negative (rebates), while taker fees eat into profits. By guaranteeing their orders won’t cross the spread, traders protect themselves from unintended costs.
2. Consistent presence on the order book enhances visibility and increases the likelihood of being filled when market conditions shift.
3. Algorithmic trading bots frequently deploy post-only settings to ensure strategies remain within predefined risk and cost parameters.
4. Exchanges such as Binance, Bybit, and Kraken support post-only functionality, enabling seamless integration into high-frequency market-making operations.
5. It helps maintain clean strategy execution, particularly in fast-moving crypto markets where slippage and misfires can lead to significant losses.

Risks and Considerations for Using Post-Only Orders

1. The main drawback is the possibility of order rejection during volatile price swings, leaving the trader unfilled when timing is critical.
2. In highly liquid markets, even small price discrepancies can cause a post-only order to fail, requiring tighter price monitoring.
3. Some traders may experience frustration when attempting urgent entries or exits and find their orders canceled due to the post-only restriction.
4. Not all trading interfaces clearly indicate when an order will be rejected under post-only rules, leading to potential confusion.
5. Over-reliance on post-only mechanics without adjusting for market depth can reduce fill rates, especially on less-traded pairs.

Frequently Asked Questions

What happens if my post-only order would execute immediately?It gets canceled automatically. Instead of acting as a taker, the system removes the order to preserve its status as a maker-level submission.

Can I use post-only orders on all cryptocurrency exchanges?Most major exchanges offer this option, but availability depends on the platform and specific trading pair. Always verify in the order entry settings before placing trades.

Do post-only orders guarantee a spot on the order book?They increase the chances significantly, but only if the price doesn't overlap with existing orders. Proper pricing relative to the current spread is essential for successful posting.

Are post-only orders suitable for retail traders?Absolutely. Any trader looking to reduce fees or practice precise order placement can benefit, not just institutional or algorithmic market makers.