Enrollment periods at a glance
| Period | When | What you can do |
|---|---|---|
| Initial Enrollment Period | 7 months: 3 before your 65th birthday month, the month itself and 3 after | Sign up for Parts A and B, and choose Part D or Medicare Advantage |
| Open Enrollment | Oct 15 – Dec 7 | Switch between Original Medicare and Medicare Advantage, change plans, join or drop Part D; changes start Jan 1 |
| Medicare Advantage Open Enrollment | Jan 1 – Mar 31 | If you’re in Medicare Advantage: switch plans once, or return to Original Medicare and join a drug plan |
| General Enrollment Period | Jan 1 – Mar 31 | Sign up for Part A or B if you missed your initial period; penalties may apply |
| Special Enrollment Periods | After qualifying events | Enroll or change after moving, losing cover, qualifying for Medicaid or Extra Help, and more |
| Medigap Open Enrollment | 6 months from the first month you have Part B and are 65+ | Buy any Medigap policy sold in your state with no medical underwriting |
Sources: Medicare.gov joining and Medigap guaranteed issue pages.
If you’re already getting Social Security
You’re usually enrolled in Parts A and B automatically when you turn 65, and your card arrives in the mail. You can decline Part B if you have qualifying employer cover. You still need to choose a drug plan or Medicare Advantage plan yourself.
If you’re still working at 65
If you or your spouse have group health cover through current employment, you can usually delay Part B without penalty. When that job or cover ends, you get an eight-month Special Enrollment Period to sign up. Important exceptions:
- COBRA and retiree health cover don’t count as current employment cover; sign up for Part B when employment ends, not when COBRA ends.
- Marketplace plans and VA benefits don’t protect you from the Part B penalty.
- At small employers (fewer than 20 employees), Medicare usually pays first, so you may need Part B at 65.
- You can’t contribute to an HSA once you’re enrolled in any part of Medicare.
Late enrollment penalties
| Part | Penalty | How long |
|---|---|---|
| Part B | 10% of the standard premium for each full 12-month period you could have had Part B but didn’t | Usually for as long as you have Part B |
| Part D | 1% of the national base premium for each full month without creditable drug cover (gaps of 63+ days) | Usually for as long as you have drug cover |
| Part A (if you pay a premium) | 10% higher premium | For twice the number of years you delayed |
Example: someone who delays Part B for 24 months without qualifying cover pays a 20% penalty. At the 2026 premium, that’s about $40.58 a month extra, for life. People who qualify for Extra Help don’t pay the Part D penalty.
How to enroll
- Apply for Parts A and B online at the Social Security website, by phone or at a local office.
- Choose Original Medicare or Medicare Advantage; see our comparison.
- With Original Medicare, add a Part D plan; see our Part D guide.
- Consider Medigap within your six-month open enrollment window; see our Medigap guide.
- Use the Medicare Plan Finder at Medicare.gov to compare plans in your area.
Open enrollment checklist for 2027
Open enrollment runs until December 7, 2026. About 3.2 million people’s Medicare Advantage plans and more than a million people’s stand-alone drug plans are ending for 2027, so read your plan’s Annual Notice of Change carefully. If you do nothing and your plan continues, you’ll be renewed automatically. Our plan-choosing checklist walks through the review.
Frequently asked questions
When should I sign up for Medicare?
During your seven-month Initial Enrollment Period around your 65th birthday, unless you have group health cover from current employment.
What happens if I miss my Medicare enrollment?
You can sign up during the General Enrollment Period (January 1 to March 31), but you may pay late penalties that usually last for life.
Do I need Part B if I’m still working?
Not if you or your spouse have group health cover through current employment at a large enough employer. Sign up within eight months of that cover ending.
Does COBRA count as creditable coverage for Part B?
No. Sign up for Part B when your employment ends, even if you take COBRA.
Can I change Medicare plans after open enrollment?
If you’re in Medicare Advantage, you can make one change between January 1 and March 31. Other changes need a special enrollment period.
Sources
- Medicare.gov – Joining a health or drug plan
- Military.com – Medicare late enrollment penalties
- Medicare.gov – Medigap guaranteed issue rights
- Medicare.gov – Medicare costs
- CMS – Medicare Advantage and Part D expected to remain stable in 2027 (Sept 2026)
- Straight Arrow News – Medicare open enrollment begins with fewer plans (Oct 2026)
- Iowa SHIIP – 5-star special enrollment period
Insurance prices, discounts and rules change often and vary by state. Figures were checked in October 2026; confirm details with the insurer or your state insurance department.