The window guide
Clara Whitfield
This guide walks through each window in the order most people meet them. Each linked page was opened and read on Nov 10, 2026. Medicare rules and dollar amounts get updated. If this summary and an official page ever differ, the official one is right.
1. Your first chance: the Initial Enrollment Period
Most people first sign up for Part A and Part B around their 65th birthday. Medicare.gov calls this the Initial Enrollment Period. In its words, "It lasts for 7 months, starting 3 months before you turn 65, and ending 3 months after the month you turn 65." (Medicare.gov: When does Medicare coverage start?, opened Nov 10, 2026)
When Part B starts depends on the month you sign up. Coverage always starts on the first of a month.
| If you sign up | Part B starts |
|---|---|
| Before the month you turn 65 | The month you turn 65 |
| In the month you turn 65, or in the 3 months after | The next month |
Birthday on the 1st? Your window moves up one month. Medicare.gov says it "starts 4 months before you turn 65 and ends 2 months after the month you turn 65." Coverage generally starts the first day of the month before you turn 65.
Some people are signed up on their own. Medicare.gov says this happens if you already get Social Security benefits at least 4 months before you turn 65. Others must sign up. Medicare.gov: How do I sign up for Medicare? (opened Nov 10, 2026)
2. Still working at 65
If you or your spouse still work and have health insurance from that job, you may be able to wait on Part B without a penalty. Medicare.gov's Working past 65 page (opened Nov 10, 2026) explains it.
The size of the employer matters. Medicare.gov says that when the employer has 20 or more employees, the job plan pays first and Medicare pays second. When the employer has fewer than 20 employees, Medicare pays first. (Medicare.gov: Who pays first?, opened Nov 10, 2026) Ask the employer's benefits office if you need Part A and Part B at 65. If you skip them, the job plan might not cover your care.
After the job ends. You get an 8-month Special Enrollment Period to sign up for Part B. Medicare.gov says it "starts when you stop working (or lose insurance), even if you choose COBRA or other coverage that's not Medicare." (Medicare.gov: Working past 65)
Some events do not open a Special Enrollment Period for Part A and Part B. Medicare.gov's list includes your COBRA or retiree coverage ending, and having or losing Marketplace coverage. (Medicare.gov: When does Medicare coverage start?, opened Nov 10, 2026)
3. The Part B late penalty, figured plainly
Medicare.gov states the rule this way: "You'll pay an extra 10% for each year you could have signed up for Part B, but didn't." The penalty is added to your monthly premium. For most people, it lasts as long as they have Part B. (Medicare.gov: Avoid late enrollment penalties, opened Nov 10, 2026)
Medicare.gov's own 2026 example:
- The standard Part B premium in 2026 is $202.90 a month.
- Someone who waited 2 full years, with no Special Enrollment Period, owes a 20% penalty: $40.58 in 2026.
- $202.90 + $40.58 = $243.48. Medicare rounds that to the nearest 10 cents, so the 2026 premium is $243.50 a month.
Some people pay more than the standard premium based on income. The 2026 premium is also listed on Medicare.gov: Medicare costs (opened Nov 10, 2026). We don't guess at 2027 amounts.
4. Windows that come back every year
| Window | Dates | What it's for | Official page |
|---|---|---|---|
| Medicare Open Enrollment | October 15 – December 7, 2026 | Join, switch or drop a Medicare Advantage Plan or a drug plan, or move between Original Medicare and Medicare Advantage. Coverage starts January 1, 2027. | Medicare.gov: Joining a plan |
| Medicare Advantage Open Enrollment | January 1 – March 31, 2027 | Only for people already in a Medicare Advantage Plan: switch plans, or "Drop your Medicare Advantage Plan and return to Original Medicare." | Medicare.gov: Joining a plan |
| General Enrollment Period | January 1 – March 31, 2027 | Sign up for Part B if you missed your first window and no Special Enrollment Period applies. Coverage starts the month after you sign up. A penalty may apply. | Medicare.gov: When does Medicare coverage start? |
| HealthCare.gov Open Enrollment for 2027 plans | November 1, 2026 – January 15, 2027. Enroll by December 15, 2026 for coverage that starts January 1, 2027. | Buy or change a Marketplace plan for 2027 | HealthCare.gov: Dates and deadlines |
All four rows were read on Nov 10, 2026. The HealthCare.gov dates are for HealthCare.gov. If your state runs its own marketplace, look up the dates on that site.
5. Before 65: your main options
- Marketplace. HealthCare.gov says that losing job-based coverage when you retire opens a Special Enrollment Period. You can apply from 60 days before to 60 days after you leave the job. A Marketplace plan can also cover you until Medicare starts. (HealthCare.gov: Coverage for retirees, opened Nov 10, 2026)
- Retiree coverage. If you drop retiree coverage on purpose, HealthCare.gov says you won't get a Special Enrollment Period for a Marketplace plan. You'd wait for the next Open Enrollment. (HealthCare.gov: Coverage for retirees)
- COBRA. COBRA lets you keep your job's group plan for a limited time after you lose it. It generally applies to employers with 20 or more employees. The U.S. Department of Labor says, "Qualified individuals may be required to pay the entire premium for coverage up to 102% of the cost to the plan." (DOL: Continuation of Health Coverage (COBRA), opened Nov 10, 2026)
- A spouse's job plan. Ask your spouse's employer how and when you can be added after you lose your own coverage.
Turning 65 while on COBRA? Medicare.gov says, "Don't wait until your COBRA coverage ends to sign up for Part B." (Medicare.gov: Working past 65)
6. Medigap's one-time window
Medigap is extra insurance from a private company. It helps pay your share of costs in Original Medicare, like copayments, coinsurance and deductibles. You generally need Part A and Part B to get it. (Medicare.gov: What's Medigap?, opened Nov 10, 2026)
Medicare.gov explains the timing: "Under federal law, you get a 6 month Medigap Open Enrollment Period. It starts the first month you have Medicare Part B and you're 65 or older." (Medicare.gov: Get ready to buy, opened Nov 10, 2026)
During those 6 months, an insurance company can't turn you down or charge you more for health problems you had before. This window happens once. It does not come back each year. After it ends, a policy may cost more, or a company may say no. Your State Insurance Department can tell you about any extra rights in your state.
7. Counseling, and help with fraud
- SHIP (State Health Insurance Assistance Program). Each state has one. SHIP describes its help as "one-on-one counseling from a trusted, unbiased source." Find your state's SHIP (the national SHIP center's site, funded by the U.S. Administration for Community Living; opened Nov 10, 2026).
- SMP (Senior Medicare Patrol). SMP programs help people spot and report Medicare fraud. Visit the SMP Resource Center (backed by the Administration for Community Living; opened Nov 10, 2026).
- Medicare.gov fraud tips. Medicare.gov says Medicare will never phone you to offer you a product or come to your home. It also warns against joining a plan by phone unless you called for help. Keep your Medicare Number private. Read Medicare.gov's fraud and abuse page (opened Nov 10, 2026).
Need help paying for Medicare? Medicaid, Medicare Savings Programs and Extra Help are outside this guide. See Medicare.gov: Get help with costs.
Quiz: three quick questions
Nobody keeps score here, and nothing is won. Every answer links to its source page.
Question 1
When does your Initial Enrollment Period start?
- A. On your 65th birthday
- B. 3 months before the month you turn 65
- C. The January after you turn 65
Answer: B. It starts 3 months before the month you turn 65 and lasts 7 months in all. If your birthday is on the 1st, it starts one month sooner. Medicare.gov: When does Medicare coverage start?
Question 2
A caller says Medicare is mailing new cards and needs your Medicare Number to send yours. Real or scam?
Answer: Scam. Medicare.gov says Medicare will never call you to offer you a product, and you should give your Medicare Number only to your doctor or people you know should have it. Hang up. Medicare.gov: Reporting Medicare fraud and abuse
Question 3
You're 66, still working, and covered by your job's health plan. The company has 50 employees. Your job ends in March. How long do you have to sign up for Part B without a late penalty?
- A. 63 days
- B. 8 months after the job or the job coverage ends, whichever comes first
- C. Until the next General Enrollment Period
Answer: B. That's the 8-month Special Enrollment Period. COBRA does not make it longer. Medicare.gov: Working past 65