You need two calculations: one to figure out the astrological sign from the birthdate and one to add the day, month, and year.
How you implement these calculations is up to you. It sounds like you would want to make a calculated field.
A calculation like this will give you the sign.
bd = birthdate;
by = Year(birthdate)
bd ≥ Date(3;21;by) and bd ≤ Date(4;19;by); "Aries";
bd ≥ Date(4;20;by) and bd ≤ Date(5;21;by); "Taurus";
/* Add lines like those above to cover all date ranges except Capricornus */
A calculation like this will give you the "routenumber".
Day(birthdate) + Month(birthdate) + Year(birthdate)