I assume you don't go to college yet since if you did you could just look up the department website for details on each major. To answer your question, it largely depends on the school and the specific concentrations/options that they offer for each of the majors you are looking at.
To give you an example plenty of people at my school "double-major" in physics and math or physics and engineering. However the Physics department at our school offers several different options. There is the "BA" which is a stupidly easy track in which all you have to take are 4 intro physics courses, 2 labs and 2 applied physics classes and you would have an official physics degree in your hand. On the other hand, there's the "BS" which requires a lot more than the BA such as upper level classes in Classical Mechanics, a year of Quantum Mechanics and E&M each, advanced labs, PDEs etc. This would be a pretty big time commitment. Similarly for math, there's a concentration where people take easier versions of analysis and algebra etc and there's a more rigorous graduate preparatory major which again is a significant time commitment. It would be very difficult to do the harder concentrations in both, but it won't add too much work if you're doing the BS in physics and you decide to add the easier version of the math major. So in summary, it may be even possible to do all 3 majors in 4 years if your school offers easier/basic concentrations for each of those majors, but would be very difficult if the only degrees that are offered or you decide to undertake are the serious concentrations.
Also, a word of advice would be to stick to two majors at most, preferably focusing more on one of them. Math, Physics and CS are three huge fields and you really want to concentrate your efforts at being good at one thing rather than having a basic understanding of everything, especially since you can only go to grad school for one of them. Even as a measly double major I'm having trouble with this since I never have time to delve deep as much as I would like to, in the subjects I study due to the fact that I have to worry about so many other things.