Unfortunately, there's not one right or wrong answer, but there are ways to figure out whether you are applying to more or less colleges than necessary.
Create a list and categorize:
Brainstorming and listing the colleges you are interested in is a great first step. We asked almost 60 high school juniors/seniors how many colleges they were applying to, and nearly 80% of them answered over five colleges, and over half of those students were applying to more than eight. Based on this data, it's safe to say that applying to at least five colleges is good. But again, there's no right or wrong answer.
What's more important than how many colleges you are applying to is how diverse your application list is. To ensure your list of colleges is excellent, a good rule of thumb is to apply to at least 1-2 college(s) pertaining to each of the following three categories:
This refers to schools where you are nearly certain you will be accepted in and/or will cost you the least. You have a stronger application than these colleges' average applicant. If you want to be even safer, consider applying to a college that is academically safe and another that is financially safe.
This refers to a college that would satisfy your academic and social needs. You're one of these colleges' average applicants. Although it may not be your first choice, you would still be satisfied with going to a college in this category. Most of the colleges you apply to should ideally belong here, given that you'll objectively most likely end up at a college in this category.
These colleges are likely your top choices, but also the most difficult. You either have a weaker application than the average student that gets accepted into these colleges, or the colleges are simply too competitive in nature and therefore it's hard to predict their response.
Other things to Consider:
While you may feel societal pressure to apply to more colleges than you'd like, applying to a lot of colleges may be financially-taxing and time consuming. Schools may typically have application fees between $50-$75, with added fees from reporting ACT, SAT, AP, and IB scores. Additionally, applications can take up A LOT of time (especially more competitive schools). Even though common applications save a lot of time, most schools ask for their own unique supplemental essays. So, if you are applying to 8 different schools, ask yourself if spending around $500 and sacrificing time and energy you could be investing towards finishing High School strong is worth it. One way to do this is by finding out which of the colleges you are choosing to apply to are a good fit for you and which one's aren't.