How much time do I have to invest in order to double-major psychology and computer science to get proficient at both of them? "As much as you can" does not resolve my confusion.

Your question is about as vague as I can imagine.  Without details on your background, native ability, goals, school, or current issues/difficulties, the possible answer ranges from "read the texts" to "impossible." Also, having a reliable expectation of employment, particularly in the current US job market, requires more than "getting the hang of" your major field of study.  You need to be proficient at the very least, and be able to outperform more experienced people by working harder at lower pay. The only useful answer I can give is that it sounds like you're in over your head and should focus on a single major. [Addendum]: So why are you interested in psychology?  Because you thought it's part of computer security? Social engineering is mostly about cons, and you're going to learn more about cons by reading a few books, or even watching Ocean's 11/12/13, than by getting a psychology undergraduate degree.  Trying to make college major or career decisions with this level of knowledge is a bad idea. I've advised a lot of undergrads, and it sounds like you don't know much about what you think you want to do.  I would focus on computer science and focus on your major courses to make absolutely sure it's what you want to do.  You should also be determining what's involved in computer security and getting trained in that, whether it's certifications or research.  Figure out what computer security is to you and how you want to participate in the field before making any further commitment.

"I pursue computer science because I am fascinated by computer security issues" Perhaps Information Technology path is a better choice than CS. Look into that as well. It is definitely possible and as a major, Psychology can be easier if you do not plan to pursue a graduate degree. If you want to plan to pursue a graduate degree, then the major requires more commitments such as research, independent field studies, etc. The highest math you need for Psychology is usually College Algebra, which is often met by meeting your general requirements while for Computer Science you need Calculus 2 (check the catalog). You often need to take a lot of Statistics courses in Psychology, such as Research Methods (1-3). Again, if you plan to pursue grad degree, you could take more advanced statistics courses to make you stand out when applying. Since Psychology was designed to prepare you to graduate school, you might as well minor in the field if you plan to stop at Bachelor's level. Human Factors Psychology Ever heard of the term User Experience? The term was coined by Don Norman, a Psychology professor. Human Factors uses the understanding of Psychology to design applications easier to use. If you do plan to stop at Bachelor's level, make sure to join a Human Factors lab or Human Computer Interaction lab. This way you can compliment the degree to your computer science. While it is definitely possible, an accurate amount of time is hard to predict. CS majors will find work more easily with just a Bachelor's degree than Psychology. However, since a lot of engineers work with UX teams these days, this will definitely be a good pair. You also need to do internships for your Computer Science degree and without it, I am not sure if any degree has any merit. Your social life will go down dramatically. College is also about being social and having fun. So if you think you can handle it, then go for it. Good luck.

I did something similar: Arts and Science double major. To answer your question, the convention in college is that for every credit a course is worth you must invest 2-3 hours outside of class to the course per week. In a quarter system college, at a full time 15 credits, you need to put in 30-45 hours outside of class. I analyzed this question constantly. I made an excel sheet for you. My assumptions: You're sleeping 8 hours a day, your instruction hours are 6-8 hours per week, you eat three times a day for approximately 1 hour for each meal, your total commute and walk time is 1 hour each day, you have a one hour morning routine, and a one hour night routine.