Your "10K day" a.k.a. "10000 day" is the 10,000th day of your life. It happens somewhere in the middle of your 28th year. Because 10,000 only happens once it's arguably due for even more of a celebration than a birthday! Not only that, since it's about halfway between birthdays it makes a fabulous excuse for another party without looking like some kind of revelling junkie. And let's face it, a year is a bit too long between birthdays anyway.

Your 20K day

Enter your birthday in year month day, e.g. 1974 4 10 for April 10th 1974:

10K:   20K:   30K:   40K:

This would probably be better with some kind of pop-up calendar but I didn't know how to do that, heh. Suggestions welcome.

Thanks to Emir for bringing this whole idea to my attention. No thanks for telling me after mine'd happened ;-)