Turning 65 and Still Working: What to Do About Medicare When You Have Employer Coverage
Henry Supinski, ChFC® · 5 min read · August 2026
Turning 65 with a good employer health plan raises a question that sounds simple and is not: do I have to sign up for Medicare now? The answer depends on the size of your employer, whether you contribute to a health savings account, and whether you have started Social Security. Get it right and you avoid paying for coverage you do not need. Get it wrong and you can owe a permanent penalty or a surprise tax bill on your HSA.
The Basic Rule: Employer Size Decides
If you are covered by a group health plan through your own or your spouse's current employment, and that employer has 20 or more employees, the employer plan pays first and Medicare is secondary. You can delay enrolling in Medicare Part B, the part that carries a monthly premium, without a late enrollment penalty for as long as that coverage continues. If the employer has fewer than 20 employees, Medicare becomes the primary payer at 65 and you generally need to enroll on time, because the employer plan may pay very little for someone eligible for Medicare who did not sign up.
Part A Is Usually Free, But Not Always Harmless
Part A, hospital coverage, has no premium for most people who worked and paid into the system. Because it is free, many people take it at 65 even while working. That is fine, unless you contribute to a health savings account. Once you are enrolled in any part of Medicare, you can no longer make HSA contributions. If your employer plan is a high-deductible plan with an HSA and you want to keep contributing, you may want to delay Part A as well, which you can do as long as you have not started Social Security benefits. Starting Social Security automatically enrolls you in Part A.
The HSA Trap: The Six-Month Lookback
When you enroll in Medicare after 65, Part A coverage is made retroactive by up to six months, but not earlier than your 65th birthday month. Any HSA contributions made during those retroactive months are excess contributions, subject to a 6% penalty every year they stay in the account. The practical rule: stop HSA contributions at least six months before you apply for Medicare or Social Security, whichever comes first. People who work to 66 or 67 and contribute to an HSA right up to their last day are the ones who get caught.
The Eight-Month Deadline After You Stop Working
When your employment or the employer coverage ends, whichever comes first, an eight-month special enrollment period begins for Part B. Enroll within that window and there is no penalty. Miss it and you wait for the next general enrollment period, may go months without coverage, and can owe a Part B late enrollment penalty of 10% of the premium for every twelve months you were eligible but not enrolled, for life. COBRA and retiree coverage do not count as current employer coverage for this purpose. Do not let COBRA lull you past the eight months.
Part D and Drug Coverage
The same logic applies to prescription drug coverage. If your employer plan's drug coverage is at least as good as Medicare's, called creditable coverage, you can delay Part D without penalty. Your employer is required to tell you each year whether the coverage is creditable. Keep that notice. When you leave the plan, you have a two-month window to enroll in Part D without penalty.
A Hypothetical Employee at 65
The details are invented; the rules are real. An engineer turns 65 in March while working for a company with several thousand employees. She has a high-deductible plan with an HSA she funds every paycheck. She has not started Social Security. She delays both Part A and Part B, keeps contributing to the HSA, and works until she retires at 67 in September. In March of her retirement year she stops HSA contributions, six months before her planned Medicare start. In September she applies for Parts A and B, coverage begins in October, and she is well inside the eight-month window. No penalty, no excess HSA contribution, no gap. The person who forgets the six-month rule and funds the HSA through September owes penalties on the last six months of contributions.
Where This Fits in the Retirement Plan
The Medicare timing decision connects to income planning in a way most people miss. Medicare premiums are set by your income from two years earlier through IRMAA, so the year you enroll, your Part B premium is based on income from your peak working years. If you retired since then and your income has dropped, that is exactly what the SSA-44 appeal is for. We map the enrollment dates, the HSA cutoff, and the IRMAA picture as one calendar for every client approaching 65, because the deadlines are unforgiving and the fixes are easy when they are planned.
Questions We Hear
Do I have to sign up for Medicare at 65 if I am still working?
Not necessarily. If you have coverage from your own or your spouse's current employer with 20 or more employees, you can delay Part B without penalty for as long as that coverage lasts. With a smaller employer, Medicare becomes primary at 65 and you generally need to enroll on time.
Can I contribute to an HSA after enrolling in Medicare?
No. Enrollment in any part of Medicare ends HSA eligibility. And because Part A can be retroactive up to six months when you enroll after 65, contributions made in those months become excess contributions. Stop HSA contributions six months before you apply.
How long do I have to enroll in Part B after I retire?
Eight months from the end of employment or the end of employer coverage, whichever comes first. COBRA does not extend that window. Miss it and a permanent late enrollment penalty can apply.
Should I take Part A at 65 even if I delay Part B?
Often yes, because it is free, unless you contribute to a health savings account and want to keep doing so. If you have not started Social Security, you can delay Part A too. If you have started Social Security, Part A enrollment is automatic.