What's the difference between ACT and SAT and when do I take one or the other?

The SAT and ACT generally test the same types of content. Both test scores are used for college admissions and merit-based scholarships. The biggest differences between the tests are that the ACT has a Science Test, and there’s one SAT Math Section for which you cannot use a calculator. 

The best way to decide if the SAT or ACT is right for you is to take a timed full-length practice test in each. Since the content and style of the SAT and ACT are very similar, factors like how you handle time pressure and what types of questions you find most challenging can help you determine which test is a better fit. For example, the pace of the SAT gives you a tad more time to think through problems, while the ACT can be more of a time crunch. Some students really thrive under the pressure of the clock, while others prefer the extra time to ponder a question.