| Period | When | What you can do |
|---|---|---|
| Initial Enrollment Period | 7 months: 3 months before the month you turn 65, that month, and 3 months after | Sign up for Part A and Part B, and join a drug plan or Medicare Advantage plan |
| General Enrollment Period | January 1 – March 31 | Sign up for Part A and Part B if you missed your first chance. Coverage starts the next month. Penalties may apply |
| Special Enrollment Period | Depends on the reason. When job-based coverage ends: 8 months | Sign up late without a penalty, for example after you or your spouse stop working |
| Open Enrollment | October 15 – December 7 | Change Medicare Advantage or drug plans, or switch between Advantage and Original Medicare. Changes start January 1 |
| Medicare Advantage Open Enrollment | January 1 – March 31 | If you're in an Advantage plan: switch to another one, or go back to Original Medicare |
| Medigap Open Enrollment | 6 months, starting the first month you're 65 or older and have Part B | Buy any Medigap policy sold in your state, with no extra charge for health problems |
When coverage starts
Sign up in the 3 months before you turn 65 and coverage can start the month you turn 65. Sign up in your birthday month or later and it starts the month after you sign up.
Do I have to sign up at 65?
If you already get Social Security, you're signed up for Part A and Part B automatically. If you or your spouse still work and have health coverage through that job, you may be able to delay Part B without a penalty, and sign up later in a Special Enrollment Period. Check with the employer's plan first.
The late penalty
For Part B, the penalty is 10% of the standard premium for each full 12 months you could have had Part B but didn't. In most cases you pay it for as long as you have Part B. Medicare's own example: wait 24 months and you pay 20% more, about $243.50 a month in 2026 instead of $202.90.
Don't miss the Medigap window
Your 6-month Medigap Open Enrollment happens once. After it, insurers in most states can charge more or turn you down because of your health. Medicare Advantage vs Medigap.
Questions
What are the 3 enrollment periods for Medicare?
The Initial Enrollment Period, a 7-month window around your 65th birthday; the General Enrollment Period, January 1 to March 31 each year, if you missed your first chance; and Special Enrollment Periods, for example when job-based coverage ends. Once you have Medicare, Open Enrollment from October 15 to December 7 lets you change plans.
What happens if I miss my Initial Enrollment Period?
You can sign up during the General Enrollment Period, January 1 to March 31, and coverage starts the month after you sign up. You may pay a late penalty: for Part B, 10% of the standard premium for each full 12 months you could have had it, for as long as you have Part B.
When can I change my Medicare plan?
During Open Enrollment, October 15 to December 7, with changes starting January 1. If you're in a Medicare Advantage plan, you can also switch to another one or to Original Medicare from January 1 to March 31.
Updated November 6, 2026. Sources: Medicare.gov, When does Medicare coverage start?; Medicare.gov, Joining a plan; Medicare.gov, When can I buy a Medigap policy?; CMS, Enrolling in Medicare Part A & Part B; CMS, Original Medicare (Part A and B) Eligibility and Enrollment.