Does taking SAT subject tests even when the college does not require it improve your admission?

I’m planning on applying out of state to universities like UC Berkeley, UC Davis, and the University of Washington, none of which require SAT subject tests for admission purposes.

However, if I were to take SAT subject tests, would that improve my chances for admission as a candidate? Or is it essentially useless on such grounds?

^I think it would help you even more considering it is a unique factor in your application and very few students applying to those same colleges will think to take those tests. SAT subject tests are never “essentially useless” because they demonstrate your achievement in a specific subject-area that otherwise college admissions officers wouldn’t have known about. That is to say that you score a 700+ on those tests.

I’m looking to enter into an engineering field, and I’m taking AP Physics E&M and Calculus BC next year as a senior (along with the AP exam). Would this already demonstrate my achievement in these specific subject areas? Should I still take SAT subject tests for Physics and Math II even though I’ll be taking their AP exams?

^I took AP Calculus BC this year (and expecting a 5 on the exam) and I’m still taking the Math Level 2 test this June. If you get a good score on the Math Level 2 subject test, it would demonstrate your math proficiency in subject areas covered before Calculus so its actually a must-have in my opinion. I’m not too sure about physics, but I’m sure the same concept applies: the more the merrier. It wouldn’t hurt to demonstrate your understanding on these tests further; plus, I’m pretty sure the AP exam for physics and the SAT subject test for physics are a bit different. Many students applying to the same colleges you are (and looking to enter into an engineering field) will probably have not taken an SAT subject test, so it may also give you a competitive edge over them.

I would also like to add that if for any reason you do not have the time to study for these subject tests and you think your time would be better spent doing extracurricular activities of some sort, those would take priority because unless there’s a requirement at the college your applying to for you to have taken these subject tests, they aren’t as important as seeming well-rounded to colleges who are increasingly using a holistic approach in their admissions.