For most people, Medicare takes effect the first of the month you turn 65. Once you enroll in any part of Medicare (Part A, Part B, or Part C), you are no longer eligible to contribute to an HSA. This includes employer contributions to your HSA. If you continue to contribute to your HSA after enrolling in Medicare, those contributions are considered “excess contributions”  and are subject to a 6% excise tax. Do you need to stop HSA contributions before age 65? This depends on when you enroll in Medicare Part A and Part B and pre-planning is recommended at least 6months prior in order to avoid any excess contributions subject to additional taxes.