With Rowling's numbers, the dating pool at Hogwarts is... pretty small.

Given that in canon Hogwarts is the only wizarding school in Britain, and that also canonically nearly every wizard goes to Hogwarts, with the very low number of students at Hogwarts there's no way that a wizarding society with large businesses/a substantial government/professional sports leagues could exist. Those trivialities are beside the point, however. As fanfiction readers and writers, they're beneath our notice. We are much more interested in the dalliances of barely postpubescent British teenagers. However, sadly, it appears that canon dictates that either a very large portion of Hogwarts's many broom cupboards remain unoccupied, or else incest is rampant. Allow me to demonstrate...

If we assume that there is a relatively large proportion of pureblooded* wizards (4 wizarding grandparents) at Hogwarts (40%), and that the average pureblooded wizard is separated from 80% of other pureblooded wizards by 3 or more generations, then if one wishes to keep bloodlines pure, or so to speak, their dating pool is limited to 18% of their peers, assuming heterosexual relationships. Let's say that the average Hogwarts student is uncomfortable dating more than 2 years outside of their age range, meaning that at most a 7th year student would consider dating a 5th year student. There are 5 boys in Harry's dormitory, which gives us a cohort of 40 students in his year. Let us assume that birth rates were especially low in that year because of Voldemort's reign of terror, and that the typical Hogwarts cohort numbers a very generous 90 students. This would make the dating pool for our pureblooded 7th year scion 3 cohorts of 90 students each. If we take 18 percent of that number, we're left with 49 possible dating partners. If our pureblooded scion is popular and good looking, then this is nothing to worry about, they'll have their chances. If not, however, then the dating scene is very, very grim. This is compounded by the fact that in a school so small, EVERYONE. KNOWS. EVERYONE. There's no avoiding someone and their friends after a nasty breakup, especially if you're in the same house. Word would also travel incredibly fast, magnifying whatever teenage awkwardness already exists.

• How do you categorize someone with 1 or 3 wizarding grandparents? I'd assume that this scenario would be far more common than the Pureblood, half-blood, and Muggleborn categories.