Use of Modified Adjusted Gross Income (MAGI) in Federal Health Programs [December 6, 2018] [open pdf - 1MB]
"Certain portions of federal health programs rely on means testing for eligibility and other purposes. Medicare premiums, the individual mandate exemptions and penalties, eligibility and amounts for tax credits for health insurance exchange coverage, and Medicaid eligibility are determined, in part, using modified adjusted gross income (MAGI). MAGI is a concept that is used throughout federal tax law and certain federal programs. There is no uniform definition of MAGI; rather, the term has different definitions depending on the purpose for which it is being calculated. For each of these federal health programs, MAGI begins with adjusted gross income (AGI) as calculated for tax purposes. From there, various types of income are included (or, in the case of Medicaid, subtracted) to calculate MAGI for each particular program. The different health programs do not necessarily define household income using the same groupings of people. For example, married couples living together are counted as the same Medicaid household regardless of whether they file a joint tax return. By contrast, married couples must file a joint tax return to be eligible for premium credits."
CRS Report for Congress, R43861
Congressional Research Service: https://crsreports.congress.gov/