Initial Enrollment Period (IEP)
Your IEP is the first time you can sign up for Medicare. It's a 7-month window centered around your 65th birthday:
- 3 months before your birthday month
- Your birthday month
- 3 months after your birthday month
During your IEP, you can sign up for Part A, Part B, Part D, a Medigap policy, or a Medicare Advantage plan.
Don't miss it. If you miss your IEP and don't have qualifying employer coverage, you may face late enrollment penalties that permanently increase your premiums. Sign up on time even if you're still working — unless your employer has 20+ employees and provides group health coverage.
Annual Election Period (AEP)
October 15 – December 7 each year. Coverage begins January 1 of the following year.
During AEP, you can:
- Switch from Original Medicare to a Medicare Advantage plan (or vice versa)
- Switch from one Medicare Advantage plan to another
- Join, switch, or drop a Part D prescription drug plan
This is the busiest enrollment period. It's the best time to review your current coverage and compare plans. Drug formularies and plan benefits change annually — a plan that worked last year may not be the best choice this year.
Medicare Advantage Open Enrollment Period (OEP)
January 1 – March 31 each year. Coverage begins the first day of the month after the plan receives your enrollment.
If you're currently enrolled in a Medicare Advantage plan, during OEP you can:
- Switch to a different Medicare Advantage plan
- Drop your Medicare Advantage plan and return to Original Medicare (and join a Part D plan)
You cannot use the OEP to go from Original Medicare to a Medicare Advantage plan — that's only available during the AEP or IEP.
Special Enrollment Periods (SEP)
You may qualify for a Special Enrollment Period if you experience certain life changes. Common qualifying events include:
- Losing employer coverage — You get an 8-month SEP when your employer coverage ends (or employment ends, whichever comes first).
- Moving — If you move to a new area with different plan options, you get a 2-month SEP.
- Qualifying for Medicaid — Becoming dual-eligible triggers an SEP.
- Leaving a Medicare Advantage plan — If your plan leaves your area or loses its Medicare contract.
- Qualifying for Extra Help (LIS) — Low-income beneficiaries who qualify get an SEP.
- Entering or leaving a nursing facility — Triggers a special enrollment window.
General Enrollment Period (GEP)
January 1 – March 31 each year. Coverage begins July 1.
This period is for people who missed their IEP and need to sign up for Part A and/or Part B. Note the delayed coverage start date — and remember that late enrollment penalties will likely apply.
Medigap Open Enrollment
Your Medigap open enrollment period is a one-time, 6-month window that starts the month you turn 65 and are enrolled in Part B. During this period:
- Insurance companies must sell you any Medigap policy they offer
- They cannot charge you more or deny you coverage because of health conditions
- They cannot make you wait for coverage to start (no waiting periods for pre-existing conditions)
Colorado note: Once your Medigap open enrollment period ends, insurance companies in Colorado can use medical underwriting to decide whether to sell you a policy and how much to charge. It's much harder to get Medigap coverage after this window closes.
Key dates for 2026
| Period | Dates | What you can do |
|---|---|---|
| MA Open Enrollment | Jan 1 – Mar 31 | Switch MA plans or return to Original Medicare |
| General Enrollment | Jan 1 – Mar 31 | Sign up for Part A/B (if you missed IEP) |
| Annual Election | Oct 15 – Dec 7 | Switch plans, join/drop MA or Part D |