Roughly every two months — though of course it depends on your innate ability to replenish blood, which can vary between people and various abilities. It's a bit longer for women — （ for totally normal biological reasons she is NOT going to get into thank you!! ） but I could easily give blood once a week if I needed to, because of my own healing, as an example.

（ also? that's cute. mental note: make sure this kind young man has candy more often. ）