Why not use the 4 digit pin and then loop, appending the first two digits to the end to get a 6 digit pin? It’s somewhat easily guessed, but is a hell of a lot better than 333333...
Mine is a friend's birthday. Not a lover/ex, not even that close of a friend. So people that know me would never guess it, and for a stranger, it is just random number.
It also have the advantage of not having to save it in a password manager, since I have it on my calender (with a lot of other birthdays saved).
Exactly. If you're going to do a birthday-based PIN, it's important to consider that the 10s digit of month and year have heavily reduced search-space.
4-digit Birthday-pins are probably good as long as they're not your birthday or that of your kids, and you do the last 2 digits of year, last digit of month, last digit of day, go capture as much of the entropy from the date as possible.
On a side note, I remember back in 2004, a colleague born on Feb 29th, 1984 was unable to enter the U.S. H1B renewal website because someone forgot about leap years in their date validation logic.
