You can use planner-deadline.el to automatically recalculate
days to a deadline by adding (require 'planner-deadline)
to
your ~/.emacs. With the default setup, make your tasks of the
form
#A0 _ Some task {{Deadline: 2004.09.12}}
(Note: There must be at least one space after the colon.)
After you run planner-deadline-update
to update task descriptions,
the task will be of the form
#A0 _ Some task {{Deadline: 2004.09.12 - 2 days}}
Regular expression for deadline data. The special deadline string should be regexp group 1. The date (YYYY.MM.DD) should be regexp group 2.