Questions about cake day! (also GA's)

So I'm fairly new to being active on this site and I've seen a few people talking about cake day and making special GA's for them. Question is, when is my cake day??? Is it linked to my Steam profile or is it when I first signed up to this website? How do I find out when my cake day is?

Thanks and here's a couple of GA's just cause you guys are awesome! :D

BlazBlue: Chronophantasma Extend (Lvl 4+)

Bridge Contructor (Lvl 1+)

High Noon VR (Lvl 3+)

L.A. Noire: DLC Bundle (Lvl 5+)

Sleeping Dogs: Definitive Edition (Lvl 4+)