- Initial Enrollment Period. Generally, when you turn 65. It lasts for 7 months, starting 3 months before you turn 65, and ending 3 months after the month you turn 65
- Open Enrollment Period. From October 15 – December 7 each year, you can join, switch, or drop a plan. Your coverage will begin on January 1 (as long as the plan gets your request by December 7)
- Medicare Advantage Open Enrollment Period. From January 1 – March 31 each year, if you’re enrolled in a Medicare Advantage Plan, you can switch to a different Medicare Advantage Plan or switch to Original Medicare (and join a separate Medicare drug plan) once during this time. Note: You can only switch plans once during this period
- General Enrollment Period. You can sign up between January 1-March 31 each year. Your coverage starts July 1. (Starting January 1, 2023, your coverage will start the month after you sign up.) You might pay a monthly late enrollment penalty, if you don’t qualify for a Special Enrollment Period
- Special Enrollment Period. There are certain situations when you can sign up for Part B (and Premium-Part A) during a Special Enrollment Period without paying a late enrollment penalty. A Special Enrollment Period is only available for a limited time. If you don’t sign up during your Special Enrollment Period, you’ll have to wait for the next General Enrollment Period and you might have to pay a monthly late enrollment penalty
- Special situations include:
- You have health insurance through a job and still working — You can sign up for Part A and Part B any time as long as:
- You have group health plan coverage
- You or your spouse (or a family member if you’re disabled) is working for the employer that provides your health coverage.
- You also have 8 months to sign up after you or your spouse (or your family member if you’re disabled) stop working or you lose group health plan coverage (whichever happens first)
- Your 8-month Special Enrollment Period starts when you stop working, even if you choose COBRA or other coverage that’s not Medicare
- You’re a volunteer, serving in a foreign country — Contact Social Security for more details.
- Certain situations for people with TRICARE — Contact TRICARE for more details.
- Situations that don’t qualify for a Special Enrollment Period:
- Your COBRA coverage or retiree coverage ends. If you miss your 8-month window when you stopped working, you’ll have to wait until the next General Enrollment Period to sign up.
- You have or lose your Marketplace coverage
- You have End-Stage Renal Disease (ESRD). Learn more about Medicare coverage for ESRD.
Source: https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start