Q&A: Facebook Birthdays
Question: “Do I have to give Facebook my birthday when I sign up? I feel like its an invasion of my privacy, and I don’t want everyone knowing my birthday.”
Answer: You must give a birthday when registering for Facebook. You can however choose to hide your birthday after you have signed-up.
Go to your profile. Under your profile picture click Edit My Profile.
On the drop down menu to the right of your birthday choose “Don’t show my birthday in my profile.” Then click Save Changes at the bottom of the page.
“Note that if you hide your birthday completely, your friends will not receive reminders when it’s approaching. If you still want them to receive these reminders, you will need to at least make the month and day visible.” Facebook Help Center