- What Is the Initial Enrollment Period?
- The 7-Month IEP Timeline
- Coverage Start Dates: When Does Medicare Actually Begin?
- What You Can Enroll In During Your IEP
- Automatic Enrollment: Are You Already Covered?
- The Birthday-on-the-1st Exception
- 6 Common IEP Mistakes (and How to Avoid Them)
- The Late Enrollment Penalty Explained
- What If You Missed Your IEP?
- Frequently Asked Questions
Turning 65 is a milestone, and with it comes one of the most important healthcare decisions you’ll ever make: enrolling in Medicare. The Initial Enrollment Period, or IEP, is your first and best opportunity to sign up. It’s a 7-month window that opens around your 65th birthday, and the timing of when you enroll within that window directly affects when your coverage starts.
Unfortunately, the rules aren’t always intuitive. Enroll a month too late and your coverage could be delayed. Miss the window entirely and you could face a penalty surcharge on your premiums that lasts for the rest of your life. This guide walks you through every detail so you can enroll with confidence.
What Is the Initial Enrollment Period?
The Initial Enrollment Period (IEP) is a 7-month window during which you can first enroll in Medicare Part A (hospital insurance) and Part B (medical insurance). For most people, this window is based on your 65th birthday. If you qualify for Medicare due to a disability, your IEP is based on your 25th month of receiving Social Security disability benefits.
Your IEP spans 3 months before your birthday month + your birthday month + 3 months after your birthday month = 7 months total.
This is not the same as the Annual Open Enrollment Period (October 15–December 7) or the General Enrollment Period (January 1–March 31). The IEP is unique to you and happens only once.
The 7-Month IEP Timeline
Let’s make this concrete. Say your 65th birthday is June 15, 2026. Your IEP would be:
Example: Birthday June 15, 2026 — IEP runs March 1 through September 30, 2026
The key insight is that not all months within your IEP are created equal. Enrolling in the first three months gives you coverage starting on the first day of your birthday month. Enroll later and your coverage start gets pushed back.
Coverage Start Dates: When Does Medicare Actually Begin?
Your Medicare coverage doesn’t automatically start the day you sign up — the effective date depends on which month of your IEP you enroll in:
| When You Enroll | Month (Example) | Coverage Starts |
|---|---|---|
| Month 1 — 3 months before birthday | March | ✅ June 1 (birthday month) |
| Month 2 — 2 months before birthday | April | ✅ June 1 (birthday month) |
| Month 3 — 1 month before birthday | May | ✅ June 1 (birthday month) |
| Month 4 — birthday month | June | ⚠️ July 1 (1 month delay) |
| Month 5 — 1 month after birthday | July | ⚠️ August 1 (2 month delay) |
| Month 6 — 2 months after birthday | August | ⚠️ September 1 (3 month delay) |
| Month 7 — 3 months after birthday | September | ⚠️ October 1 (4 month delay) |
Example based on a June 15 birthday.
Enroll in the first three months of your IEP to get coverage on the first day of your birthday month with no gap. If you wait until your birthday month or later, your coverage won’t begin until the following month — leaving you potentially uninsured.
Maria turns 65 on June 15, 2026. She enrolls in Medicare Part B in March (Month 1). Her coverage starts June 1 — right on time, no gap.
Her neighbor Tom also turns 65 in June but doesn’t enroll until August (Month 6). His coverage won’t start until September 1 — leaving him without Medicare for three full months.
What You Can Enroll In During Your IEP
During your IEP you can sign up for any or all of the following:
Medicare Part A (Hospital Insurance)
Covers inpatient hospital stays, skilled nursing facility care, hospice, and some home health care. Most people don’t pay a premium for Part A if they or their spouse paid Medicare taxes for at least 10 years (40 quarters).
Medicare Part B (Medical Insurance)
Covers doctor visits, outpatient care, preventive services, and durable medical equipment. The standard premium is $202.90/month in 2026, with higher amounts for higher-income beneficiaries (IRMAA surcharges).
Medicare Part C (Medicare Advantage)
An alternative to Original Medicare offered by private insurers, bundling Part A, Part B, and usually Part D with extras like dental, vision, and hearing. Learn more about how Medicare Advantage plans work and see our Advantage vs. Supplement comparison.
Medicare Part D (Prescription Drug Coverage)
Covers prescription medications as a standalone plan with Original Medicare, or bundled inside a Medicare Advantage plan. Like Part B, delaying Part D without creditable drug coverage triggers a permanent late enrollment penalty.
Your IEP is the only time you can enroll in Part A, Part B, a Medicare Advantage plan, and a Part D plan all at once — without needing a qualifying life event.
Automatic Enrollment: Are You Already Covered?
If you’re already receiving Social Security retirement benefits or Railroad Retirement Board benefits at least four months before your 65th birthday, you will be automatically enrolled in Medicare Part A and Part B. Your Medicare card should arrive by mail about three months before you turn 65.
If you are not receiving Social Security benefits when you turn 65 — for example, if you’re still working and have delayed claiming Social Security — you will not be automatically enrolled. You must sign up during your IEP.
Many people who delay Social Security assume they’ll be automatically enrolled in Medicare. They won’t be. If you’re still working at 65 and haven’t claimed Social Security, you must proactively sign up during your IEP — or risk permanent penalties.
The Birthday-on-the-1st Exception
If your 65th birthday falls on the first day of a month, Medicare treats your eligibility as though you were born in the previous month — shifting your entire IEP one month earlier.
Linda’s birthday is June 1, 2026. Instead of her IEP running March through September, it runs February 1 through August 31. Her coverage can start as early as May 1 — the month before she turns 65.
Compare this to someone born on June 2, whose IEP runs March through September with coverage starting June 1.
If your birthday is on the 1st, your IEP begins and ends a month earlier than you might expect — mark your calendar carefully.
6 Common IEP Mistakes (and How to Avoid Them)
COBRA continuation coverage, individual Marketplace (ACA exchange) plans, and retiree health plans are not considered creditable employer coverage for Medicare purposes. Having these does not protect you from the late enrollment penalty.
What to do: If your only coverage is COBRA, a Marketplace plan, or a retiree plan, enroll in Medicare during your IEP. See the full list of Medicare enrollment mistakes to avoid.
If you aren’t receiving Social Security, you won’t be automatically enrolled in Medicare — and many people don’t realize they need to take action themselves.
What to do: Even if you delay Social Security, sign up for Medicare during your IEP. You can enroll in Medicare without claiming Social Security benefits.
The Special Enrollment Period only applies if you are the active employee, or the coverage is through your spouse’s current employer. If your spouse has retired and you’re on their retiree coverage, that does not qualify.
What to do: Verify coverage is through active employment at a company with 20+ employees. If it’s retiree coverage, enroll during your IEP.
As the table above shows, enrolling in months 4–7 of your IEP delays when your coverage begins — potentially leaving you uninsured for months.
What to do: Enroll in the first three months of your IEP for the earliest possible coverage start date.
If you later decide you need Part B, you’ll pay a 10% penalty for every full 12-month period you were eligible but not enrolled — and that penalty lasts for as long as you have Part B.
What to do: Unless you have qualifying employer coverage through active employment, enroll in Part B during your IEP.
If you go 63 or more consecutive days without Part D or other creditable drug coverage after you’re first eligible, you’ll pay a Part D late enrollment penalty — 1% of the national base beneficiary premium for each uncovered month.
What to do: When you enroll in Part A and Part B, also enroll in a Part D plan or a Medicare Advantage plan that includes drug coverage.
The Late Enrollment Penalty Explained
For every full 12-month period that you could have had Part B but didn’t sign up, your monthly premium increases by 10%. This is added to your standard Part B premium and you pay it for as long as you have Part B — for most people, that means for life.
Over 20 years, that 2-year delay would cost an additional $9,739 in penalty surcharges — and the amount grows each year as the standard premium rises. There is no cap.
The Part B late enrollment penalty is permanent. It does not expire after a set number of years. The only exception is if you qualify for a Medicare Savings Program (MSP), which can eliminate the penalty.
What If You Missed Your IEP?
If your IEP has already closed, you still have options — though they come with trade-offs.
Special Enrollment Period (SEP)
If you delayed Medicare because you had health coverage through an employer where you or your spouse were actively working (at a company with 20+ employees), you qualify for a Special Enrollment Period. The SEP gives you 8 months after the employment or coverage ends to enroll in Part B without a penalty. See our full guide to all Medicare enrollment periods.
General Enrollment Period (GEP)
If you don’t qualify for an SEP, you can enroll during the General Enrollment Period: January 1 through March 31 each year. Coverage starts the first of the month after you sign up. You will likely face the late enrollment penalty. Check our Medicare deadlines calendar for current dates.
Appealing a Penalty
If you believe the penalty was applied in error — for example, if you did have qualifying employer coverage — you can appeal within 60 days of receiving the penalty notice with documentation of your employer coverage.
If you’re approaching 65 and still working with employer coverage, request a letter from your employer confirming your group health plan coverage and employment status. This documentation is essential if you ever need to prove eligibility for an SEP.
Frequently Asked Questions
Can I enroll in Medicare online?
Yes. You can enroll through the Social Security Administration at ssa.gov, by calling Social Security at 1-800-772-1213, or by visiting your local Social Security office in person.
I’m still working at 65. Do I need to enroll?
It depends. If you have health coverage through your current employer (or your spouse’s current employer) and the employer has 20 or more employees, you can generally delay Part B without penalty. When your employment or employer coverage ends, you’ll have an 8-month Special Enrollment Period to sign up. Read more in our Part B enrollment guide.
What if I have coverage through the VA or TRICARE?
VA coverage does not count as creditable coverage for avoiding the Part B penalty. If you only have VA benefits, you should still enroll in Part B during your IEP. TRICARE for Life requires you to enroll in both Part A and Part B to maintain eligibility.
Can I sign up for just Part A and delay Part B?
Yes — this is a common strategy for people still working with employer coverage. Premium-free Part A has no late enrollment penalty, so many people sign up for Part A at 65 and delay Part B until their employer coverage ends. Just confirm your employer coverage qualifies before delaying Part B.
I’m under 65 and have a disability. How does my IEP work?
If you qualify for Medicare through disability, your IEP is based on your 25th month of receiving Social Security disability benefits. The 7-month window begins 3 months before that 25th month, includes that month, and ends 3 months after. If you have ALS, there is no 24-month waiting period — coverage begins the same month your disability benefits start.
What’s the difference between my IEP and the Annual Enrollment Period?
The IEP is your first and only chance to join Medicare — tied to your eligibility date. The Annual Enrollment Period (October 15–December 7) is when existing beneficiaries switch plans or change Part D coverage — not for initial enrollment in Part A or Part B. See our guide to all Medicare enrollment periods.
Not Sure When Your IEP Opens?
Talk to a Licensed Independent Medicare Advisor — free of charge. We’ll confirm your enrollment window, walk through your options, and help you avoid costly mistakes before deadlines pass.
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