Many students are confused about the pros and cons of applying to a particular college without declaring a major. The reality is, in most cases, making this choice does not affect the acceptance decision.
Things get tricky, however, if you are absolutely set on a particular major and that major is more competitive than others at the school. At some schools, rejection from your declared major precludes you from being considered for other majors at that school. In plain English, if you don't get into the major you selected, you don't get into the school at all.
The majors most often affected by this issue are engineering (and all of its subspecialties) and the arts. If these represent strong interests for you, you should declare. While it might be tempting to apply undeclared or to a less competitive major with the hope of transferring to the preferred major later, this option is extremely risky. A competitive major remains competitive, whether you’re applying or trying to switch. What’s more, you will have to keep up with the major’s requirements at a high GPA while you bide your time – and still run the risk of not getting in.
Policies on majors vary from school to school, even within the same state system. For example, here’s a quote from an assistant director of Freshman recruitment for UCLA:
“If a student is not accepted into the film program they will not be considered for their second choice major. This goes for admissions for any student who is applying for admission into one of UCLA’s specialty schools which are (1) Arts and Architecture, (2) Engineering, (3) Nursing, and (4) Theater, Film, and Television.”
Not so for fellow UC San Diego:
“UCSD does not admit applicants by major. In fall 2014, about 19 percent of freshman applicants applied as Undeclared.
… Applicants to oversubscribed majors in the Jacobs School of Engineering may be offered an alternate major if they are not selected for their first choice majors”
There are a lot of variables that may affect this “major” decision. Put together a list of factors specific to you, and make the best choice you can knowing what you know today. And, if you’re still unsure, don’t hesitate to ask questions of the admissions office – that’s what they’re there for.