Joke about it. Say something like, "Well you know today's my birthday." She'll probably be a little upset she forgot but will try to make it up to your tomorrow and the rest of today. Good luck

>>17354211
This.

Just remember, birthday's aren't really a big deal. At least you have a girlfriend to forget yours.

>>17354189
She'll feel even guiltier if she doesn't realize until way later that you guys never celebrated your birthday this year. Like a piece of shit for not acknowledging you the whole day. Tell her and let her make it up to you, she'll feel bad but desu that is pretty shitty, forgetting your bf or gf's birthday (unless it's very out of character).