“Navigators” and others helping people apply for health coverage need to understand basic tax filing rules because eligibility for Medicaid, the Children’s Health Insurance Program (CHIP), and premium tax credits for coverage bought through federal and state Marketplaces is based on Internal Revenue Code definitions of income and household. We’ve developed The Health Care Assister’s Guide to Tax Rules to help fill this need. The guide provides basic information on relevant tax rules, including when someone is required to file taxes, what filing status options are available, the rules for claiming someone as a tax dependent, and what sources of income are taxable and therefore counted in determining eligibility for Medicaid, CHIP, and premium tax credits. It also shows how Medicaid uses an individual’s tax filing status to determine who is in his or her household, and how Medicaid’s household rules differ from those used for premium tax credits. Understanding these issues can help health care assisters work with applicants for health coverage, especially those who have complicated family situations or unpredictable sources of income or are not familiar with filing taxes.