Enroll in Medicare during your Initial Enrollment Period, which starts three months before the month you turn 65 and ends three months after

Your Initial Enrollment Period is a seven-month window centered on your 65th birthday. It begins on the first day of the third month before you turn 65 and ends on the last day of the third month after. For example, if you turn 65 in June, your period runs from March 1 through August 31. You must enroll during this window to avoid permanent penalties on your premiums.

If you miss this window, you can still enroll later, but you will pay a higher monthly premium for as long as you have Medicare. The penalty is 10 percent of the Part B premium for each full 12-month period you were may be able to access but did not enroll. This penalty stacks and never goes away, even if you enroll years later. The same rule applies to Part D (prescription drug coverage) — you pay a 1 percent monthly penalty for each month you delayed, added to your premium permanently.

There is one major exception: if you or your spouse are still working and covered by an employer health plan, you may be able to delay enrollment without penalty. This is called creditable coverage. You must enroll within eight months of losing that coverage or retiring, whichever comes first, to avoid the penalty. Your employer's benefits office can tell you whether your plan qualifies.

Key Takeaways

  • Your Initial Enrollment Period is seven months long, centered on your 65th birthday, and missing it triggers permanent premium penalties.
  • If you are still working and covered by your employer's health plan, you may delay Medicare enrollment without penalty as long as you enroll within eight months of losing that coverage.
  • Part B and Part D penalties are calculated differently but both are permanent — they add to your monthly premium for life.
  • You can enroll online through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

What happens if you enroll before age 65

You cannot enroll in Medicare before age 65 unless you have been receiving Social Security Disability Insurance (SSDI) for at least 24 months, or you have end-stage renal disease or ALS. If you meet one of these conditions, Medicare begins automatically — you do not need to take action. SSDI beneficiaries are enrolled in Part A and Part B on the first day of the 25th month of receiving benefits.

If you do not meet these conditions and you are not yet 65, you will need to stay on your current health coverage — whether that is an employer plan, the Affordable Care Act marketplace, or Medicaid — until you reach 65. At that point, your Initial Enrollment Period begins.

Enrolling if you are still working at 65

If you are still employed and your employer offers health insurance, you have two paths. The first is to enroll in Medicare Part A only and keep your employer coverage as primary. Part A covers hospital stays and is usually free if you have paid Medicare taxes for at least 10 years. This protects you if you need hospitalization while still working.

The second path is to delay both Part A and Part B if your employer plan is considered creditable coverage. Creditable means it is at least as good as Medicare's standard coverage. Your employer's human resources or benefits department can confirm this in writing. If you choose to delay, you must enroll within eight months of leaving the job or losing coverage — not eight months from your 65th birthday. Missing this important date triggers the permanent Part B penalty.

Part D (prescription drug coverage) has its own rule: if your employer plan covers drugs at least as well as Medicare Part D, you can delay Part D without penalty. If it does not, you should enroll in Part D during your Initial Enrollment Period to avoid the 1 percent monthly penalty.

Enrolling after you miss your Initial Enrollment Period

If you did not enroll during your seven-month window and you do not have creditable coverage, you enter a different enrollment system called General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. This means if you miss your Initial Enrollment Period by even one day and enroll in January, you will have a gap in coverage from your 65th birthday until July 1.

During this gap, you are responsible for all medical costs. Hospital bills, doctor visits, and prescriptions are your expense. Many people in this situation face thousands of dollars in bills before coverage starts. The permanent premium penalty also begins accruing when ready when you turn 65, whether or not you are enrolled.

If you have a life event — such as losing employer coverage, moving to a new state, or losing Medicaid — you may be able to enroll outside the normal windows through a Special Enrollment Period. You must report the change to Medicare within 60 days. Life events that may have access to include losing group health coverage, moving out of your plan's service area, or becoming a U.S. citizen or legal resident.

How to enroll during your Initial Enrollment Period

You can enroll through three channels: online at Medicare.gov, by phone at 1-800-MEDICARE (1-800-633-4227), or in person at your local Social Security office. Online enrollment is the fastest — you can complete it in about 15 minutes if you have your Social Security number and information about any current health coverage.

When you enroll, you will choose between Original Medicare (Part A and Part B) or a Medicare Advantage plan (Part C). Original Medicare lets you see any doctor who accepts Medicare. Medicare Advantage is an all-in-one alternative run by private insurance companies — it usually includes prescription drug coverage and may have lower out-of-pocket costs, but it limits you to a network of doctors and requires referrals for specialists. You do not have to decide when ready; you can enroll in Original Medicare now and switch to Advantage later during the annual open enrollment period (October 15 through December 7).

You will also choose whether to enroll in Part D (prescription drug coverage) if you go with Original Medicare. If you take regular medications, enrolling during your Initial Enrollment Period protects you from the permanent penalty. If you do not take prescriptions now but think you might later, you can still enroll in Part D and pay the premium even if you do not use it — the penalty applies only if you go without coverage and then enroll later.

Special situations: working past 65 or living abroad

If you are a federal employee, railroad employee, or work for certain other employers, your enrollment rules may differ. Federal employees covered under the Federal Employees Health Benefits Program (FEHB) should contact their agency's benefits office before turning 65 — they have different important date and options. Railroad employees covered under the Railroad Retirement Act should contact the Railroad Retirement Board.

If you live outside the United States, you can still enroll in Medicare Part A and Part B, but you cannot enroll in Medicare Advantage or most Part D plans. You must enroll during your Initial Enrollment Period or face penalties. Some U.S. territories have different rules; contact Medicare directly if you live in Puerto Rico, the U.S. Virgin Islands, Guam, American Samoa, or the Northern Mariana Islands.

What to have ready before you enroll

Gather your Social Security number, birth date, and citizenship or immigration status before you start. If you are enrolling by phone or in person, have your current health insurance information available — the name of your plan, your member ID, and your group number if you have employer coverage. If you are explore for Part B and have not yet started receiving Social Security benefits, you will need to provide information about your income to determine whether you may have access to for a subsidy that lowers your premium.

If you are enrolling in Part D, have a list of your current medications and the pharmacies where you fill them. This helps you choose a plan that covers your drugs at the lowest cost. You can compare Part D plans on Medicare.gov without enrolling — the tool shows you the estimated annual cost for your specific medications under each plan in your area.

Frequently Asked Questions

What if I turn 65 in the middle of the month?

Your Initial Enrollment Period is based on the calendar month you turn 65, not the specific date. If you turn 65 on any day in June, your enrollment period runs from March 1 through August 31. Enroll as soon as possible after your birthday to may support coverage starts on the first of the following month.

Can I change my mind after I enroll?

Yes, but only during specific windows. If you enroll in Original Medicare, you can switch to Medicare Advantage during the annual open enrollment period (October 15 through December 7) or if you have a may have access to life event. If you enroll in Advantage, you have one month after enrollment to switch back to Original Medicare. After that, you are locked in until the next open enrollment period.

Do I have to enroll in Part B if I am still working?

No, if your employer plan is creditable coverage. You can enroll in Part A only and delay Part B without penalty, as long as you enroll in Part B within eight months of losing your employer coverage. If your employer plan is not creditable, you should enroll in Part B during your Initial Enrollment Period to avoid the permanent penalty.

What if I do not know when my Initial Enrollment Period is?

Call 1-800-MEDICARE and provide your birth date. They will tell you the exact dates of your seven-month window. You can also log into your Medicare.gov account if you have created one — it shows your enrollment period and any coverage you already have.

Is there a penalty if I enroll early in my Initial Enrollment Period?

No. You can enroll as soon as your period begins — three months before you turn 65 — and there is no penalty for enrolling early. Coverage typically begins the first of the month in which you turn 65 or the first of the following month, depending on when you enroll.