You are welcome! Residency for tax purposes is different than for immigration purposes. To be a tax resident of the US. you need to pass the substantial presence test. You must be in the US for 183 days or more determined by the following calculation:
You will be considered a United States resident for tax purposes if you meet the substantial presence test for the calendar year. To meet this test, you must be physically present in the United States (U.S.) on at least:
1. 31 days during the current year, and
2. 183 days during the 3-year period that includes the current year and the 2 years immediately before that, counting:
• All the days you were present in the current year, and
• 1/3 of the days you were present in the first year before the current year, and
• 1/6 of the days you were present in the second year before the current year.
So if you arrived in the US in 2017 and have not had many travels outside of the US, you would definitely be a US tax resident for 2018 as you would have had more than 183 days in the US. Whether you should have filed as a nonresident in 2017, depends on when you arrived in the US. If you arrived by June 2017, you were probably in the US for 183 days in 2017 and should have filed as a full year resident. If not, you should have filed a nonresident return in 2017. TurboTax does not handle nonresident returns.
