Hermione hated birthdays. She never understood why they were necessary. So by some miracle a person was able to slither out of the birth canal? Didn't mean that the rest of the world had to celebrate. She was terrible at remembering when they were happening, even her own. Most years she completely forgot her husband's. She knew it was in late February... the 24th, perhaps? Or was it the 28th? Didn't really matter. Every year it came and went without her making much of a fuss about it. The only reason she remembered her son's birthday was because of the active role she played in his birth. Otherwise? She would probably forget it too.