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What are Post Only Orders?

From the perspective of trading fees, all orders on Delta Exchange can be classified into one of the following two categories:

Maker orders:

These are orders that are not executed immediately and are added to the order book. Since maker orders increase the liquidity on the exchange, Delta rewards such orders with lower trading fees for futures. This means that traders receive a discount on trading fee when a maker order gets executed.

Taker orders:

These are orders that are matched immediately against an existing order. Since these orders reduce the liquidity on the exchange, they are required to pay positive trading fees. This means that traders pay taker fee when a taker order gets executed. Click here to know more about maker and taker fees. Post only orders are ALWAYS executed as maker orders. This means:
  1. Post only orders always receive maker fee on execution
  2. Only limit orders can be post-only. Since market orders execute immediately, they can’t be made post only
  3. If a post only order will partially or fully match against an existing order in the order book, then the post only order is cancelled.

How to make an order post only?

An order can be made post only by checking the post-only flag in the order placement section. [video width="3792" height="1746" mp4=""][/video] Post Only Order Examples
  1. Without Post Only Flag
In the situation below, a trader wishes to buy 10000 quantity of BTCUSD at $7300. Since a sell order of 6003 contracts at $7300 already exists in the order book, the trader’s order will be partially filled immediately. The trader will immediately receive a fill of 6003 contracts of BTCUSD at $7300. The trader will be paying taker fees on this fill. The remaining limit buy order for 3097 contracts at $7300 will enter the order book. Whenever this remaining order will execute it will be a maker order and thus, will receive maker fees.
  1. With Post Only Flag
If the trader places the same order, i.e. buy 10000 contracts of BTCUSD at $7300 with post only flag enabled, the order will be cancelled. This is because the order will match immediately against an existing sell order in the order book.
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