You can take the SAT as often as you like, but you have to check each college's policy on multiple scores and use of Score Choice. Read more on Score Choice on our blog.
About 80% of high school juniors take the SAT two times and only about 40% take it three or more times. Most students take the SAT in the spring of their junior year and in the fall of their senior year. That allows enough time between tests to prepare for the next test and allow for a significant score improvement, which is the only good reason to repeat the SAT.
What are the SAT Subject Tests?