Overview of Eligibility and Tax Rules Related to Coverage for Domestic Partners, Civil Unions, Spouses, and Common-law Marriage

This is an in-depth summary on eligibility and taxation rules related to spouses (same-sex and opposite-sex), common law marriage, domestic partners (same-sex and opposite-sex), states with civil union / domestic partner rights and rules surrounding documenting these relationships. Sample affidavits to for documenting are also included at the end. The taxation and eligibility rules surrounding offering benefits to spouses, domestic partners, and those in a civil union differ on the federal level and vary from state to state.  This document describes the general rules and taxation implications for offering group health plan benefits (including account-based plans) to these various individuals based on federal and state laws as of March 2025.