Health Insurance and Medicare Basics: Key Enrollment Deadlines
Part of our insurance guides. Health coverage runs on enrollment windows. Miss one and you can wait months for coverage, pay a penalty for years, or lose a right to buy a policy without health questions. This page lays out the deadlines that matter most and links to a deeper guide on each.
We do not sell health or Medicare plans, and nothing here recommends a plan. For free one-on-one help, contact your State Health Insurance Assistance Program (SHIP) through shiphelp.org, or use Medicare.gov and HealthCare.gov directly.
Key takeaways
- Your Medicare Initial Enrollment Period lasts 7 months: 3 months before the month you turn 65, that month, and 3 months after, per Medicare.gov.
- The Part B late penalty is 10% for each full 12 months you could have had Part B and did not, and it usually lasts as long as you have Part B.
- Your Medigap Open Enrollment Period is a one-time 6-month window. After it, insurers can generally use medical underwriting.
- Losing job-based coverage opens a 60-day Special Enrollment Period for a Marketplace plan, per HealthCare.gov.
What are the main health insurance enrollment periods?
| Window | Dates | What it is for | Source |
|---|---|---|---|
| Medicare Initial Enrollment Period | 7 months around your 65th birthday month | First chance to sign up for Part A and Part B | Medicare.gov |
| Medicare General Enrollment Period | January 1 to March 31 | Sign up for Part B if you missed your first chance; a penalty may apply | Medicare.gov |
| Medicare Open Enrollment | October 15 to December 7 | Join, drop or switch Medicare Advantage and drug plans; coverage starts January 1 | Medicare.gov |
| Medicare Advantage Open Enrollment | January 1 to March 31 (only if already in Medicare Advantage) | Switch Medicare Advantage plans or return to Original Medicare | Medicare.gov |
| Medigap Open Enrollment Period | 6 months, starting the first month you have Part B and are 65 or older | Buy any Medigap policy sold in your state without medical underwriting | Medicare.gov |
| Marketplace Open Enrollment | November 1 to January 15 | Enroll in or change a HealthCare.gov plan for any reason | HealthCare.gov |
| Marketplace Special Enrollment Period | 60 days before or after losing qualifying coverage | Enroll after a job loss or other life change | HealthCare.gov |
When should you sign up for Medicare?
For most people the first deadline is the Initial Enrollment Period. Medicare.gov describes it as 7 months, "starting 3 months before you turn 65, and ending 3 months after the month you turn 65." If you already get Social Security benefits at least 4 months before 65, Medicare.gov says you are enrolled in Part A and Part B automatically.
Missing the window costs money. Medicare.gov says the Part B penalty is "an extra 10% for each year" you could have signed up and did not, and that penalties are usually charged for as long as you have that coverage. Working past 65 with job-based coverage can give you a Special Enrollment Period instead, but Medicare.gov is explicit that COBRA "isn't considered group health plan coverage."
Our Medicare enrollment timeline for turning 65 walks through each month, when coverage starts and how the penalties are calculated.
What is the difference between Medigap and Medicare Advantage?
Once you have Part A and Part B, you choose how to get your coverage. Original Medicare lets you see any provider that takes Medicare, and you can add a Medigap policy to help with costs like the 20% coinsurance. Medicare Advantage plans use networks, have a yearly out-of-pocket limit, and usually include drug coverage. Medicare.gov says you can only buy Medigap if you have Original Medicare, so it does not pair with Medicare Advantage.
The choice at 65 matters because the rights to change it later are narrow. Our guide to Medigap vs Medicare Advantage basics compares the two on networks, costs and switching rights, without recommending either.
Can you switch Medigap plans later without health questions?
Federal law gives you one Medigap Open Enrollment Period. Medicare.gov calls it "a one-time enrollment period" that "doesn't repeat every year." Outside it, an insurer can deny you a policy if you do not meet its medical underwriting, unless you have a guaranteed issue right.
Some states add their own annual window tied to your birthday. Our table of Medigap birthday rule states lists each state we could confirm from a state insurance department or statute, with the window length and the plans it covers.
Check your state first: Medicare.gov tells readers to check with their State Insurance Department because "You may have additional rights under state law." Federal rules are the floor, not the whole picture.
What happens to your health insurance if you lose your job?
You usually have three routes. COBRA lets you keep your employer's plan for a limited time; the U.S. Department of Labor says it usually lasts up to 18 months and that you have 60 days to elect it. A Marketplace plan opens through a Special Enrollment Period, and HealthCare.gov says you can enroll within 60 days of losing job-based coverage. Medicaid and CHIP accept applications any time.
Our guide to health insurance options after losing your job lays out the deadlines side by side and what to compare before you pick.
Guides in this section
- Turning 65: your Medicare enrollment timeline
- Medigap vs Medicare Advantage: the basic differences
- Medigap birthday rule states
- Lost your job? Health insurance options and deadlines
FAQ
Is Medicare Open Enrollment the same as the Medigap Open Enrollment Period? No. Medicare Open Enrollment runs October 15 to December 7 every year and covers Medicare Advantage and drug plans. The Medigap Open Enrollment Period is a one-time 6-month window that starts the first month you have Part B and are 65 or older, per Medicare.gov.
Do I have to sign up for Medicare if I get Social Security? If you get Social Security benefits at least 4 months before you turn 65, Medicare.gov says you get Part A and Part B automatically.
When can I enroll in a Marketplace plan outside Open Enrollment? Only with a Special Enrollment Period. HealthCare.gov says losing qualifying coverage in the past 60 days, or expecting to lose it in the next 60 days, can qualify you.
Does COBRA count as job-based coverage for Medicare? No. Medicare.gov says COBRA isn't considered group health plan coverage for the Part B Special Enrollment Period, and getting COBRA doesn't change when that period ends.
Where can I get free help choosing coverage? Your State Health Insurance Assistance Program offers local Medicare counseling. Find yours at shiphelp.org. For Marketplace plans, start at HealthCare.gov.
Sources
- Medicare.gov, "When does Medicare coverage start?", accessed October 1, 2026. https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start
- Medicare.gov, "Joining a plan," accessed October 1, 2026. https://www.medicare.gov/basics/get-started-with-medicare/get-more-coverage/joining-a-plan
- Medicare.gov, "Get ready to buy" (Medigap), accessed October 1, 2026. https://www.medicare.gov/health-drug-plans/medigap/ready-to-buy
- Medicare.gov, "Avoid late enrollment penalties," accessed October 1, 2026. https://www.medicare.gov/basics/costs/medicare-costs/avoid-penalties
- HealthCare.gov, "Special enrollment opportunities," accessed October 1, 2026. https://www.healthcare.gov/coverage-outside-open-enrollment/special-enrollment-period/
- U.S. Department of Labor, Employee Benefits Security Administration, "COBRA Continuation Coverage," accessed October 1, 2026. https://www.dol.gov/agencies/ebsa/laws-and-regulations/laws/cobra
- SHIP Technical Assistance Center, "Get Medicare Help from Your Local SHIP Program," accessed October 1, 2026. https://www.shiphelp.org/
This page is general information, not insurance, legal or enrollment advice. FinanceRazor does not sell or recommend health or Medicare plans. For help with your situation, contact your State Health Insurance Assistance Program, Medicare.gov or HealthCare.gov.