Display contacts birthdays on stock Samsung calendar app I'm using a SM-G920V Galaxy S6 with Android version 6.0.1.  When I open the calendar app that comes with the phone, tap "More" in the upper right corner and then "Manage Calendars", there's an option to turn "Contact's birthdays" on and off.  To me, that would indicate that it has the capability to display your contact's birthdays on the calendar app.  However, I've got it set to "On" and only a few of my contact's birthdays are showing up.

Can anyone tell me how to get all my contact's birthdays to show up?
You probably figured it out by now, but the calendar of birthdays only syncs with the Samsung account. 

The fastest way to link a different account to the Samsung account I could find without re adding contacts was by adding a relationship to the contacts you want to set up.

I did this by going to my  Contacts app, clicking on my own profile, and under the relationships section adding a relationship. I did it with my family members and they started showing up right away.