When does my Medicare Initial Enrollment Period start?

Your Initial Enrollment Period (IEP) is a 7-month window that begins 3 months before the month you turn 65, includes your birthday month, and ends 3 months after. Enrolling in the first 3 months ensures your coverage starts on the first day of your birthday month. Waiting until the last 3 months may delay your coverage start date.

What is the Medicare General Enrollment Period?

The General Enrollment Period (GEP) runs January 1 – March 31 each year. It's for people who missed their Initial Enrollment Period and don't qualify for a Special Enrollment Period. Coverage begins the first of the month following enrollment, and a late enrollment penalty may apply.

What is a Medicare Special Enrollment Period?

A Special Enrollment Period (SEP) allows you to enroll in Medicare outside the standard windows due to qualifying life events — most commonly, losing employer health coverage. You typically have 8 months to enroll in Part B after your employer coverage ends without facing a penalty.

What is the Annual Enrollment Period for Medicare?

The Annual Enrollment Period (AEP), also called Open Enrollment, runs October 15 – December 7 each year. During this window, anyone already on Medicare can switch between Original Medicare and Medicare Advantage, change their Part D drug plan, or enroll in a plan for the first time. Changes take effect January 1.

Medicare Resources

Medicare Enrollment Periods Explained

Q: What happens if I miss my Medicare enrollment window?

If you miss your Initial Enrollment Period without qualifying employer coverage, you'll have to wait for the General Enrollment Period (January–March) to sign up for Part B, and your coverage won't begin until July. You may also face a permanent late enrollment penalty. Missing Part D enrollment can similarly result in a lifelong premium surcharge.

Medicare enrollment isn't open year-round. Miss the wrong window and you could face a permanent penalty, a coverage gap, or a months-long wait. Here are the four periods you need to know.

The Four Enrollment Windows

7-month window around your 65th birthday

Initial Enrollment Period (IEP)

Opens 3 months before your birthday month, includes your birthday month, and closes 3 months after. This is the most important window — missing it without qualifying employer coverage triggers penalties.

January 1 – March 31 annually

General Enrollment Period (GEP)

For people who missed their IEP. Coverage begins the first of the month after you enroll, and a late enrollment penalty typically applies. This is the safety net, not the plan.

Triggered by qualifying life events

Special Enrollment Period (SEP)

Most commonly used when losing employer coverage. You have 8 months to enroll in Part B after employer coverage ends — no penalty if you had creditable coverage during the delay.

October 15 – December 7 annually

Annual Enrollment Period (AEP)

Open to anyone already on Medicare. Switch between Original Medicare and Medicare Advantage, change your Part D plan, or enroll for the first time. Changes start January 1.

Interactive Enrollment Timeline

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Key Dates to Know

IEP opens3 months before 65th birthday month

IEP closes3 months after 65th birthday month

AEP opensOctober 15 each year

AEP closesDecember 7 each year

GEP windowJan 1 – Mar 31 each year

SEP after job loss8 months from coverage end

Free Resource

Turning 65 Medicare Checklist

Use this timeline-based checklist to make sure you hit every step before your coverage needs to be in place. Check off each item as you go.

3+ months before turning 65

Confirm your Medicare eligibility date (3 months before your 65th birthday month)

Check whether you have qualifying employer coverage (employer with 20+ employees) that allows you to delay Part B without penalty

Contact your HR department to verify whether your employer plan is considered creditable coverage

Begin researching Original Medicare vs. Medicare Advantage and what fits your situation

1–3 months before turning 65

List your current doctors, specialists, and hospitals — verify they accept your chosen plan

List all prescription medications and check which Part D plans cover them at the best cost

Decide between Original Medicare + Medigap + Part D vs. Medicare Advantage

If choosing Original Medicare, begin shopping Medigap plans — your 6-month guaranteed-issue window opens when you're 65 and enrolled in Part B

Your birthday month (or sooner)

Enroll in Part A and Part B at SSA.gov, by phone (1-800-772-1213), or at your local Social Security office

If you're already receiving Social Security benefits, confirm whether you were automatically enrolled

Enroll in a Medicare Advantage or Medicare Supplement plan

Enroll in a Part D prescription drug plan (if not included in your Medicare Advantage plan)

After enrollment

Set up automatic premium payment through Social Security or direct billing

Save your Medicare card and plan ID cards in a secure location

Add your plan's member services phone number to your contacts

Mark October 15 on your calendar — that's when Annual Enrollment opens each year to review or change your plan

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Medicare Enrollment — Common Questions

When does my Initial Enrollment Period start?

Your IEP is a 7-month window that opens 3 months before the month you turn 65, includes your birthday month, and closes 3 months after. Enrolling in the first 3 months ensures coverage starts on the first day of your birthday month. Waiting until the last 3 months may delay your start date by 1–3 months.

What is the General Enrollment Period and when should I use it?

The GEP runs January 1–March 31 each year and is for people who missed their Initial Enrollment Period and don't have a qualifying Special Enrollment Period. Coverage begins the first of the month after you enroll, and a late enrollment penalty typically applies. Think of it as a last resort, not a plan.

Can I delay Medicare if I'm still working at 65?

Yes, if your employer has 20 or more employees and you're covered under their health plan. In that case, you can delay Part B without a penalty and use a Special Enrollment Period when that coverage ends. If your employer has fewer than 20 employees, Medicare typically becomes primary at 65 and delaying Part B is risky.

What is the Annual Enrollment Period and do I need to do anything?

The AEP (October 15 – December 7) is your chance to review and change your Medicare coverage for the following year. Plans change their premiums, networks, and formularies annually — even if you're happy with your plan, an annual review with a local agent ensures it still fits your doctors, drugs, and budget.

What happens if I miss my Medicare enrollment window?

Missing your IEP without qualifying employer coverage means waiting for the General Enrollment Period (January–March), with coverage delayed until July. You'll also likely face a permanent Part B late enrollment penalty of 10% per year of delay. Missing Part D enrollment can similarly result in a lifelong premium surcharge.

More Medicare Resources

Part B Penalty CalculatorSee the permanent cost of delaying Part B Eligibility CalculatorFind out exactly when you qualify Premium CalculatorEstimate your Part A and B premiums Enrollment AssistanceLocal help navigating your enrollment Medicare EligibilityWho qualifies and under what conditions All Medicare ResourcesCalculators, timelines, and tools