Happy birthday Problem

Happy Birthday to every User

Imagine that you are having a social network web application with 100.000 users. These users have store their personal information to your application like their name, username, access password, hobbies, interests AND their date of birth.

Imagine that you want to check everyday for every user, if it has it's birthday or not and if yes you want to give him a free premium account of your app for the next week.

Although you might already know how to accomplish this task for a specific user it is going to be extremely hard to achieve for 100.000 users. That means that you need to write 100.000 conditions and from them, detect which ones have birthday on the give day in order to give them the premium account.

That doesn't sound very efficient right?