As an F-1 student, how many calendar years can I exclude days before I become a tax resident?

F-1 and J-1 students are 'exempt individuals' whose U.S. days don't count toward the substantial presence test for up to five calendar years, and even a single day in a year burns a whole year of the five. Any part of a calendar year counts as a full year against your five-year limit. After that fifth year, your days start counting and you typically become a resident alien once you pass the test. Teachers and trainees on J visas get a shorter two-year exemption. To keep the exemption you must file Form 8843 each year, even with no income. The IRS covers exempt individuals in Publication 519 at irs.gov.