When Should I Sign Up for Medicare? Your Enrollment Timeline

Updated for 2026. Missing your Medicare enrollment deadlines can result in permanent penalties, coverage gaps, and months without insurance. This comprehensive guide covers every enrollment period, when they are, who they apply to, and exactly what to do to avoid costly mistakes.

Medicare Enrollment Is Not Like Other Insurance

Unlike employer health insurance or ACA Marketplace plans, Medicare has multiple enrollment periods with very specific rules. You can’t just sign up whenever you want. Miss the right window and you could wait months for coverage, and pay a higher premium for the rest of your life.

There are five main enrollment periods you need to understand: a 7-month Initial Enrollment window, a 10% Part B penalty per year for late enrollment, and an Annual Enrollment Period that starts October 15.

1. Initial Enrollment Period (IEP): When You First Become Eligible

Your Initial Enrollment Period is a 7-month window centered around the month you turn 65:

• Starts: 3 months before your 65th birthday month
• Includes: Your birthday month
• Ends: 3 months after your birthday month

When Coverage Begins (Timing Matters)

When You Enroll	Coverage Start Date
1-3 months before birthday month	First day of your birthday month
During your birthday month	1st of the following month
1 month after birthday month	1st of the 2nd month after enrollment
2 months after birthday month	1st of the 3rd month after enrollment
3 months after birthday month	1st of the 3rd month after enrollment

Pro tip: Enroll during the first 3 months of your IEP to ensure coverage starts on or before your 65th birthday. If you wait until after your birthday month, there will be a gap in coverage.

What to Enroll In During Your IEP

• Part A: Enroll even if you have employer coverage (unless you have an HSA). It’s free.
• Part B: Enroll unless you have employer coverage from a company with 20+ employees.
• Part D or Medicare Advantage: Choose a drug plan (or MA plan that includes drugs) to start the same month as Part B.
• Medigap (if choosing Original Medicare): Your 6-month Medigap Open Enrollment Period begins the month your Part B starts. This is your BEST chance to get guaranteed issue Medigap coverage regardless of health.

2. Special Enrollment Period (SEP): After Losing Employer Coverage

If you delayed Medicare because you had employer coverage (from a company with 20+ employees), you qualify for a Special Enrollment Period when that coverage ends.

Part B Special Enrollment Period

• Duration: 8 months from the date your employer coverage ends OR the date your employment ends (whichever comes first)
• No penalty: You won’t face a late enrollment penalty if you enroll during this period
• Coverage start: Can begin as early as the 1st of the month after you enroll

Critical warning: COBRA and retiree coverage do NOT qualify you for a Special Enrollment Period. If you retire and go on COBRA, you must enroll in Medicare within your IEP or during the General Enrollment Period. COBRA is not considered “current employer” coverage.

Part D Special Enrollment Period

You also get a 63-day SEP for Part D when you lose creditable drug coverage. You must show evidence that your previous plan was creditable (your former employer sends you a creditable coverage letter annually).

3. Annual Enrollment Period (AEP): October 15 to December 7

The Annual Enrollment Period (also called “Open Enrollment” or “Fall Enrollment”) runs from October 15 through December 7 every year. Changes take effect January 1 of the following year.

What You CAN Do During AEP

• Switch from Original Medicare to a Medicare Advantage plan
• Switch from Medicare Advantage back to Original Medicare
• Switch from one Medicare Advantage plan to another
• Join a standalone Part D drug plan
• Switch from one Part D plan to another
• Drop Part D coverage (not recommended)

What You CANNOT Do During AEP

• Enroll in Part A or Part B for the first time (that’s your IEP)
• Switch Medigap plans with guaranteed issue (in most states)
• Change your Part B enrollment status

Why AEP Matters Every Year

Plans change their formularies (drug lists), provider networks, premiums, and copays every year. Even if you’re happy with your current plan, it could change in ways that cost you more money. Every Medicare beneficiary should review their plan during AEP.

We recommend our clients schedule a free annual plan review during September to be ready when AEP starts. Check out our AEP Checklist for a step-by-step guide.

4. Medicare Advantage Open Enrollment Period (OEP): January 1 to March 31

This period is only for people 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 add a standalone Part D plan)

You CANNOT use this period to go from Original Medicare to a Medicare Advantage plan. That requires waiting until AEP or having a Special Enrollment Period.

5. General Enrollment Period (GEP): January 1 to March 31

If you missed your IEP and don’t qualify for a Special Enrollment Period, the General Enrollment Period is your safety net, but it comes with consequences:

• When: January 1 through March 31 each year
• Coverage starts: July 1 (meaning 3-6 months without coverage)
• Penalties: You’ll pay the Part B late enrollment penalty permanently (10% for every 12-month period you were eligible but not enrolled)

Medigap Open Enrollment: Your One Best Chance

This is separate from all the enrollment periods above and is critically important:

• When: 6-month window starting the month you turn 65 AND have Part B
• What it means: Insurance companies MUST sell you any Medigap plan they offer at the best rate, regardless of health conditions
• Why it matters: After this window closes, insurers in Alabama can use medical underwriting to deny coverage, charge more, or exclude pre-existing conditions

If you’re turning 65 and choosing Original Medicare + Medigap, this 6-month window is the single most important enrollment period in your Medicare journey. Do not miss it.

Enrollment Period Calendar: Quick Reference

Period	Dates	Who It’s For	Changes Effective
IEP	7 months around 65th birthday	New Medicare enrollees	Varies (see table above)
SEP	8 months after losing employer coverage	People leaving employer plans	As early as following month
AEP	October 15 - December 7	All Medicare beneficiaries	January 1
MA OEP	January 1 - March 31	Current MA enrollees only	1st of month after enrollment
GEP	January 1 - March 31	Those who missed IEP	July 1
Medigap OEP	6 months from 65 + Part B	New Part B enrollees at 65	Immediate

Frequently Asked Questions

I turned 65 last year and didn’t sign up. What do I do?

If you don’t have qualifying employer coverage, you’ll need to wait for the General Enrollment Period (January 1, March 31). Coverage won’t start until July 1, and you’ll face a permanent late enrollment penalty. Contact us immediately to minimize the damage and get you enrolled as quickly as possible.

Can I change my Medigap plan during AEP?

AEP is for Medicare Advantage and Part D changes, not Medigap. You can apply for a different Medigap plan at any time, but outside of your initial Medigap Open Enrollment Period, insurers in Alabama can use medical underwriting. If you have health issues, you may not qualify for a new Medigap plan.

I have a Medicare Advantage plan but want to switch to Original Medicare + Medigap. When can I do this?

You can switch during AEP (October 15, December 7) or during the MA Open Enrollment Period (January 1, March 31). However, getting a Medigap plan after your initial 6-month window may require medical underwriting. Talk to us about your options before making the switch.

My spouse turns 65 in June. When should they start the enrollment process?

Their IEP starts 3 months before their birthday month, so March 1. We recommend starting the planning process in February to review all options. Ideally, they should apply for Part B in March or April so coverage begins June 1 (their birthday month). If choosing Medigap, apply during that same period for guaranteed issue rights.