In Facebook's targeting, there's an audience in Demographics called "Upcoming Birthday", which accumulates all the people that have a birthday within the next week.
This gives us a cool opportunity to capture people's attention with a birthday creative (because they'll be receptive to birthday style content) whilst giving them a discount opportunity for your product.
Here's a brief rundown:
1. Setup your campaign with the Conversion objective.
2. Create your ad-set with one of the following target audiences:
a) Video Viewers + Upcoming Birthday
b) Page Engagers + Upcoming Birthday
3. Make sure you have a creative that's Birthday centric, either balloons, presents, parties, birthday cake etc.
4. Then offer them a discount. I tend to use a 10% off, using a code of 'BDAY10'.