I currently have a 84% in AP Calculus AB, and I really don't think I can get an A this semester. I don't know if I should drop out of the class so that my UW GPA stays a 4.0, or if I should accept it and have a GPA of around a 3.95. Would a lower GPA ruin my chances of getting into a top 20 school? Would a B in AP Calculus look bad to colleges if I plan on doing pre-med?
Stay in the game. Getting a B or B+ in AP Calc is perfectly okay. I'd only recommend dropping if you had a C, D or failing grade right now.
Colleges will not care about a couple of Bs. The average GPA at all the Ivys is between 3.85-3.93, not a 4.0. They don't care about perfect grades as much as seeing that you challenged yourself with the most rigorous classes offered by your high school environment.
Good luck.
Do not drop, a 3.9-4.0 is excellent regardless of where you apply. The only way it would affect you is your rank like you're probably not going to be valedictorian. But who cares? It's just a number. The rest of your application, especially that you chose to take AP calc, says a lot more about you. And I can't imagine that your weighted GPA, if you have one, will suffer much if at all.
To keep this community safe and supportive: