Part I of a two-part series on rules for determining a consumer’s Modified Adjusted Gross Income (MAGI). MAGI applies when determining eligibility for advance payments of the premium tax credit (APTC) and cost-sharing reductions (CSRs) for health coverage purchased through the Marketplace, as well as eligibility for the Children’s Health Insurance Program (CHIP) and Medicaid. Part I focuses on using MAGI to calculate a consumer’s total household income. Part II of the MAGI series walks through the rules for determining household composition, including differences in the Marketplace and Medicaid/CHIP households. This webinar series was provided as part of the navigator and assister training series by the Center for Medicare & Medicaid Services Weekly Marketplace Webinar trainings for assisters.