Substantial Presence Test (SPT)

You meet the SPT (and are taxed as a resident) if you've been physically present in the US for ≥31 days in the current year AND ≥183 days using the SPT formula (current year + 1/3 prior year + 1/6 year-before-that). If you depart partway through the year, you may be 'dual-status' for tax purposes — different brackets, different deductions. CRITICAL: get a CPA familiar with NRA rules to model both scenarios before you depart.