by Awaken » Thu Oct 14, 2010 3:44 pm
If you are just saying it in regular conversation or in response to a question about when your birthday is, you would use "is." In general it is usually in response to a question.
"When was your birthday?" - "My birthday was January 9th." (Correct)
"When is your birthday?" - "My birthday is January 9th." (Also correct)
Both are correct. It is context dependent.