Changing the price in a limit order

Question

I have a question about a limit order, or any non-market order for that matter, like a GTC limit order.

My question is that, if I change the price, or quantity, of a limit order, will the system immediately reset the queue position of my order in the order book to the very end, or will the system still keep the queue position of my order in the order book at its original position?

If latter, will people abuse this system? For example, people place GTC limit orders, and they keep adjusting the price according to the market condition, while still maintaining their orders' front-of-line queue position, so that when the price meets, their orders will be filled first.

Answer 1

This depends on the stock exchange in question. Generally if you modify an existing order [including GTC], these are internally treated as Cancel/Replace Orders. Depending on the action, you may lose the time priority position and a new position would get assigned. More here.

(f) Cancel/Replace Orders. Depending on how a quote or order is modified, the quote or order may change priority position as follows:

(1) If the price is changed, the changed side loses position and is placed in a priority position behind all orders of the same type (i.e., customer or non-customer) at the same price.

(2) If one side's quantity is changed, the unchanged side retains its priority position.

(3) If the quantity of one side is decreased, that side retains its priority position.

(4) If the quantity of one side is increased, that side loses its priority position and is placed behind all orders of the same type at the same price.

Answer 2

On a typical price-time priority exchange:

• If you change the price of the limit order you go to the back of the line (at that price).

• If you change the size of a limit order, usually a decrease in size will result in no change, but an increase in size will either put the order at the back of the line (at that price) or put the increase in quantity at the back of the line at that price.

Each exchange has their own rules, and some do not use price time priority at all.