I am on my F-1 visa. I started school in Sep of '13, and graduated in sep of '17. I started working in Apr of '18. Am I a non-resident alien or resident alien?Thanks!

[DanaB]

You can file as a resident since you met the substantial presence test in 2018.

On an F-1 visa, you are 5 years exempt after that you can meet the substantial presence test to become a resident for tax purposes. The 183 days start to count after the 5 years have passed, in your case on Jan 1, 2018.  Please see IRS Alien Residency Examples F1 visa for additional information.