You are exempt for 5 years on a F1 visa. This is a lifetime exemption, so once you used up the 5 years, you cannot be exempt again on a F1. Therefore after the 5 years, the substantial presence test starts. You should have been a resident for tax purposes in 2017. Please see these examples on the IRS website: <a rel="nofollow" target="_blank" href="
https://www.irs.gov/individuals/international-taxpayers/alien-residency-examples">https://www.irs.go...>
