Many of our clients come to U.S. on a tourist visa, yet they are required to file U.S. resident tax return. The IRS uses two tests — the green card test and the substantial presence test — for assessing your alien status. If you satisfy the requirements of either one, you’re considered a resident alien for income tax purposes; otherwise, you’re treated as a non-resident alien. If you are an alien with a green card, meaning the U.S. Citizenship and Immigration Service allows you to reside in the country legally, you are a resident alien. However, if you don’t have a green card and spend at least 31 days in the U.S. during the current tax year and a total of 183 days during the last three tax years (inclusive of the current tax year), you’ll usually satisfy the physical presence test and are also treated as a resident alien. However, 183 days calculation is not a simple one, it takes into consideration total number of days in a current year and only a fraction of days in the previous two years.