Most people become eligible for Medicare at 65, and your first chance to sign up is built around your birthday — not around the fall enrollment season you hear advertised.
Your first chance to sign up is your Initial Enrollment Period (IEP) — a 7-month window built around your birthday:
If your birthday is in June, your window runs March 1 through September 30. The earlier in your window you sign up, the sooner your coverage starts — signing up before your birthday month generally starts coverage on the first day of that month.
One exception to "you have to sign up": if you're already receiving Social Security benefits when you turn 65, you're generally enrolled in Part A and Part B automatically, and your Medicare card arrives by mail. If you're not receiving benefits yet, nothing happens automatically — you sign up through Social Security.
If your IEP closes and you don't have coverage that qualifies you for a Special Enrollment Period, the fallback is the General Enrollment Period — January 1 through March 31 each year. Coverage starts the month after you enroll, which can leave a real gap.
The longer cost is penalties:
Missing the window isn't fatal. It's just expensive in slow motion — which is why the timeline is worth learning before your birthday, not after. Full period-by-period detail: Enrollment periods →
Plenty of people work past 65 with employer health coverage. Whether you can safely delay Medicare depends mainly on one number: how many people work for the employer.
Your group plan generally stays primary, and you can usually delay Part B without a penalty. When the job or the coverage ends, an 8-month Special Enrollment Period opens for you to enroll — and if that window closes unused, the penalties above apply.
Medicare is generally expected to pay first once you turn 65, even while you're still on the company plan. Delaying Part B here can leave you with coverage gaps — your employer plan may pay as if Medicare already paid its share — on top of penalties.
COBRA and retiree coverage do not count as employer coverage for delaying Part B. The 8-month clock starts when employment or group coverage ends — not when COBRA runs out.
If you contribute to a health savings account, enrolling in Medicare ends your eligibility to contribute. And if you delay Part A past 65 and sign up later, Part A coverage can backdate up to 6 months — HSA contributions made in that backdated window can create a tax problem. Many people stop HSA contributions at least 6 months before applying for Medicare. This one deserves a conversation with your tax professional before your birthday, not after.
Your 6-month Medigap open enrollment period starts the month you're 65 or older and enrolled in Part B. During it, insurers generally can't deny you or charge more because of your health. When you start Part B decides when that protected window runs — one more reason the timing is a decision, not a default.
New to the basics? Start with the ABCD of Medicare →
One page: Parts A through D, the Medigap vs. Medicare Advantage tradeoffs, and the enrollment timeline — in plain English, to keep.
Educational information about how Medicare works — not a plan recommendation or enrollment guidance. Reserve Investment Group, Inc. is a private insurance agency and is not affiliated with the federal government or the federal Medicare program. Medicare plan availability, costs, and coverage vary by state and county and can change over time. For official information, visit Medicare.gov or call 1-800-MEDICARE (1-800-633-4227).
