Modified adjusted gross income (MAGI), for purposes of the NIIT, is generally defined as adjusted gross income (AGI) for regular income tax purposes increased by the foreign earned income exclusion (but also adjusted for certain deductions related to the foreign earned income). For individual taxpayers who haven't excluded any foreign earned income, their MAGI is generally the same as their regular AGI.
https://www.irs.gov/taxtopics/tc559
