Fastest way / best practice to calculate "next birthdays"

The subject basically says it all, I'm looking for the fastest
(indexable) way to calculate the next birthdays relative to NOW() from a
dataset of about 1 million users.

I'm currently using a function based index, but leap year handling /
mapping February 29 to February 28 gives me some headaches.

Is there any best practice to do that in PostgreSQL?


--
Best regards,
Hannes Dorbath