I only need to remember the birthdays of a handful of people, so I can easily remember them. I do write them on the calendar, just so I can keep in mind how long I've got, but I know the dates and everything.
That would be a 50 - 50.
I can my remember family birthdays, but friends...well that's very
different !
I have to use my calendar, and each year it takes
forever, to write down all the birthdays.