Employee's Part A Medicare entitlement is retroactively effective six months prior to her application for Medicare benefits (age 67 ½), because she applied for Medicare and Social Security benefits more than 6 months after becoming initially eligible.

Can you opt out of retroactive Medicare coverage?

As you plan your Social Security and Medicare enrollments, be sure to stop contributing to your Health Savings Account beginning six months before you enroll in Medicare. That way, you don't have to withdraw any contributions based on retroactive Part A coverage.

What is retroactive Medicare?

Part A, and you can enroll in Part A at any time after you're first eligible for Medicare. Your Part A coverage will go back (retroactively) 6 months from when you sign up (but no earlier than the first month you are eligible for Medicare).