The last month you can contribute
HSA eligibility is monthly. Once Medicare Part A starts, that month usually does not count as an HSA-eligible month. The last month that typically still counts is the month before Part A starts. Confirm with the IRS, your HSA administrator, and a tax professional.
Social Security can pull Part A backward
If you start Social Security, Part A can be awarded retroactively for up to six months — not before you are eligible. That can make the last HSA month earlier than the month you expected. Ask Social Security what your Part A start month will be before you contribute.
Taking Part A while you delay Part B
Many people take premium-free Part A at 65 even if they delay Part B because of a large employer’s coverage. Part A alone is enough to stop HSA contributions. If you want to keep funding an HSA, talk with Social Security and the benefits office before you enroll in Part A.
Spending from an HSA is different
Stopping contributions is not the same as losing the account. You can often still spend existing HSA funds on qualified medical expenses. Contribution rules and spending rules are separate. Confirm with the administrator.