The typical advice, and I agree with it, is to apply to 6 to 8 schools. But make sure you choose those schools carefully.  This may sound obvious, but do not apply to it in case you cannot picture yourself being happy at a school. Also, don't apply to a school simply because it has a great reputation or it's where your mom went or it's where all your friends are going. Begin with 15 or so possible choices and narrow down your list after carefully researching schools, visiting their campuses and talking with students. Apply to those schools that are a good match for your personality, interests and career goals. Furthermore be sure to apply to a selection of schools that will maximize your chances of being accepted somewhere. Look at the profiles that each school has and compare the admissions data to your own academic record and test scores. A wise selection of schools might look something like, for example, research schools. These are schools with highly selective admissions. Your grades and scores are below the averages for these schools. You find that there's a possibility you'll get in, but it's a bit of a long shot when you study the admission data.

To how many colleges should you apply

Be realistic because you're almost guaranteed a rejection letter in case you got a 450 on your SAT Math and you apply to a school where 99% of applicants got over a 600. On the other hand, you should still identify schools like Harvard and Yale in case you have remarkably strong scores. These top schools are so competitive that no one has a good chance of being admitted (learn more about when a match school is actually a reach. Your academic record and test scores are right in line with the averages when you look at the profiles for these colleges.  You feel that you measure up favorably with typical applicants for the school and that you have a decent chance of being admitted. Be sure to keep in mind that identifying a school as a "match" does not mean you will be accepted. Many factors go into an admissions decision, and many qualified applicants get turned away. Safety schools are schools where your academic record and scores are measurably above the average of admitted students. Realize that highly selective schools are never safety schools, even in case your scores are above the averages. Most elite schools have application fees of $60 or more. You'll also need to pay for extra score reporting when you apply to a lot of schools: $15 for AP and $11 for ACT and SAT. The applications, especially at competitive schools, take a lot of time to complete. Do you really have several hours to devote to each of those 15 applications? Most select schools have supplements to the application that ask questions about why you feel you are a good match for the school, or what specifically about the school you find appealing.