Choosing between "Post-Only" and "Immediate-or-Cancel" (IOC) depends on whether you want to be a maker and save on fees or a taker and prioritize execution.
1. First, Understand the Core Differences
Post-Only
If your order would immediately match against an existing order on the order book, the system will cancel it outright.
The goal is to ensure you always act as a "maker" and enjoy maker fees. If you place a limit price better than the current market price, the order sits on the book waiting to be filled by others, and you pay the maker fee when it's executed. If your order would be filled immediately, it gets canceled and won't trade.
Immediate-or-Cancel (IOC)
Any portion that can be filled is filled, and the unfilled remainder is canceled immediately.
This aims to execute as much as possible without posting an order on the book. It's suitable when you need fast execution and can accept partial fills. If the available liquidity is insufficient for your full order quantity, the leftover is canceled and won't stay on the book.
Prerequisite: You're on the OKX spot or futures order panel and preparing to use an advanced limit order.
2. When to Choose "Post-Only"
If you want to save on fees and are not in a hurry to execute
Under standard fee rates, maker fees are usually lower than taker fees. Post-Only guarantees you are always the maker and never accidentally become a taker.
This suits limit orders to buy low/sell high, market-making strategies, and grid strategies. If the market is volatile, the order may get repeatedly canceled because it would fill immediately, causing it not to get posted—this is normal.
3. When to Choose "Immediate-or-Cancel"
If you want fast execution and don't mind getting split into multiple fills
For example, you want to buy at a certain price and are willing to take as many sell orders as available at that price, without leaving a resting order for the remainder.
This suits quick position building/closing, momentum trading, and highly liquid coins. If the order book depth is shallow, only a small portion may fill, and the rest will be canceled immediately.
4. Comparison
| Post-Only | Immediate-or-Cancel (IOC) | |
|---|---|---|
| Purpose | Save on fees, act as maker | Prioritize execution, not necessarily full fill |
| Execution | Does not execute immediately; sits on order book | Fills as much as possible instantly |
| Unfilled portion | Remains on book waiting | Canceled immediately |
| Fee | Maker fee | Taker fee |
| Best for | Passive order strategies, market making | Fast trades, high liquidity |
Common failure reasons: If you select "Post-Only" and the order never fills, it's not because the system is stuck—it's because your limit price is worse than the current market price and no one is willing to accept it. If you need to get filled quickly, switch to IOC or market order.
Risk reminder: In Post-Only mode, if orders are repeatedly canceled, you might miss the entry opportunity. In IOC mode, if only part of your order fills and the rest is canceled, you may need to place additional orders, increasing operational costs and fees.
How to confirm your choice was correct after placing the order?
Check your [Current Orders] panel: If your order is resting on the order book, Post-Only worked and it's waiting to be filled. If the order disappears without any fill, Post-Only canceled it because it would have taken liquidity immediately. If the order shows "partially filled" with zero remaining, IOC worked—everything possible was filled, leftovers canceled. If you wanted quick execution without leaving a residual order, IOC was right; if you want to save on fees and can be patient, Post-Only is the way.
