I will be applying to Columbia University and University of Washington St. Louis. Both of them don’t require SAT Subject Tests. So should I take them or not?
If I take them then will they improve my admission chances?
Wash U says they don’t consider subject tests: https://admit.washington.edu/apply/freshman/how-to-apply/test-scores/
Columbia stopped recommending them but still say that they will consider subject tests in the context of your application: https://undergrad.admissions.columbia.edu/apply/first-year/testing
If you don’t have any other schools on your list that recommend subject tests, I personally wouldn’t bother.
It will only help your application, but if your application is exceptionally strong, it will certainly not “improve” your chances. What will hurt, particularly for universities which consider interest, is getting the name wrong. It’s Washington University in St. Louis.