Order modification
Family II · Orders
Not to be confused with order execution, order validity.
Order modification is the act of changing one or more parameters of a working order before it is filled or cancelled. It applies to orders that are still live in the market, not to filled or cancelled orders. Depending on the venue, a modification may preserve the order's original time priority or may cause it to lose priority and be treated as a new order.
What can be modified
Typical modifiable parameters include:
- Price — for limit and stop orders.
- Quantity — the number of shares, contracts, or units.
- Time-in-force — for example, changing a day order to good-till-cancelled, where the venue supports it.
- Stop or trigger price — for stop and stop-limit orders.
Some venues also allow modification of display quantity or order type. Rules on which fields can be changed, and whether a change counts as a cancel-and-replace, vary by broker and market.
Priority and cancel-and-replace
At many exchanges, reducing the size of an order keeps its time priority, while increasing the size or changing the price causes it to lose priority and re-enter the queue at the back. Some systems implement every modification as a cancel-and-replace, which always resets priority. The exact behaviour is venue-specific and should be confirmed with the broker or exchange.
Worked example
Often confused with
- order execution
- Order execution is the process by which a broker or venue receives a client order and carries it out, determining the price, timing, and manner in which the order is filled or rejected.
- order validity
- Order validity is the attribute of a trading order that determines how long it remains eligible for execution, specifying whether it persists until filled, until a set time, or until the trading session ends.