Originally Posted by
sincx
Probably something to do with time zones and how your birthday is stored in their system.
If your birthday is stored as an exact time (i.e. Jan. 1 1980 12:00 AM UTC) in United's system, the app might be stupid enough to convert that into local time (Dec. 31 1979 4:00 PM PST) and display an incorrect date.
+1. Excel also has a nasty habit of doing this occasionally.