Default value for DATETIME type NOW() + 7 days

When creating a new table like this:

CREATE TABLE myTable (
   id INT(11) AUTO_INCREMENT,
   deadline DATETIME,
   PRIMARY KEY(id)
)

I want to set a DEFAULT value for deadline, such that it will be NOW() + 7 days, how can I achieve this?

I've tried this:

deadline DATETIME DEFAULT (NOW() + INTERVAL 7 DAY)

and this:

deadline DATETIME DEFAULT DATE_ADD(NOW(), INTERVAL 7 DAY)

where none of them seems to be working.