+1 to pretty much everything that has already been said.
In addition though, for those majors whose curriculum does not cover the pre-reqs, like many non-science majors and some other science majors like engineering or physics, it will most likely take more than the 4 years to graduate. For me, physics only covered the physics, math and gen chem pre-reqs, so I had too add a whole year of extra classes for Ochem, Biochem, Bio, Physio, Micro, and genetics. With an average of 12-16 units every quarter, plus 3 summer quarters, its taking me 5 years total + a gap year since my pre-reqs wont be done till the end of this year (4th year) and I still need to take the MCAT.
My freshman year I put together an excel spreadsheet of all the classes I needed to graduate + the pre-reqs, and organized them into each quarter to get an estimate as to when I will graduate. If you have the time, I recommend doing this or speaking with an advisor to set something like this up just to steer you in the right direction.