I have a date field in to which i am entering customer birth dates (day,month,year)

I want to be able to sort these dates to show their birth day and month. At the moment, when I filter the list of customers in a table that shows FIRST NAME, SURNAME, BIRTHDAY, it is sorting them chronologically acording to their birth year.

I want to sort chronologically by day and month - i.e 

January 4

February 10

February 22

April 11

so I can see who's birhday is next.

thanks!