Your Medicare enrollment window depends on when you turn 65

You must enroll in Medicare during a specific window around your 65th birthday. The window opens three months before the month you turn 65 and closes three months after. If you turn 65 in June, for example, your enrollment window runs from March through September. Missing this window can cost you money in penalties for the rest of your life, even if you don't use Medicare right away.

The Social Security Administration automatically enrolls you in Medicare Part A (hospital insurance) and Part B (medical insurance) the month you turn 65, but only if you are already receiving Social Security benefits. If you are not yet taking Social Security, you must enroll yourself during your window or face late penalties on Part B.

People who are still working and covered by an employer health plan have different rules. You can delay Part B enrollment without penalty if your employer plan covers 20 or more employees and you are actively employed. When you leave that job or the coverage ends, you have eight months to enroll in Part B without penalty — this is called a Special Enrollment Period.

Key Takeaways

  • Your initial enrollment window is seven months long: three months before, the month of, and three months after you turn 65.
  • If you miss your window and do not have employer coverage, you pay a 10 percent penalty on Part B premiums for life, plus a 1 percent penalty per month for Part D (drug coverage).
  • You do not need to enroll in Part B if you are still working and covered by an employer health plan with 20 or more employees.
  • Social Security automatically enrolls you in Part A and Part B at 65 if you are already receiving Social Security, but you still must choose a Part D plan or face drug coverage penalties.

What happens if you enroll late

A late enrollment penalty on Part B stays with you permanently. If you miss your window by one year, you pay an extra 10 percent on your Part B premium every month for life. If you miss it by two years, you pay 20 percent extra. This penalty does not go away even if you enroll later — it compounds your monthly bill forever.

Part D (prescription drug coverage) has a similar penalty: 1 percent of the national average premium for each month you go without coverage. If you go 24 months without Part D, your penalty is roughly 24 percent of that average, and again, it stays with you for life. These penalties explore even if you never use the coverage.

The only way to avoid these penalties is to show that you had creditable coverage — health insurance that is at least as good as Medicare Part B or Part D — during the time you were not enrolled. Employer plans, TRICARE, the Veterans Health Administration, and some other plans count as creditable. You will need proof from your former plan to show Medicare.

When to enroll if you are still working

If your employer offers health insurance and you are actively employed, you can skip Part B enrollment and wait. You do not pay a penalty for delaying Part B as long as your employer plan covers 20 or more employees. Part A (hospital insurance) is different — you should still enroll in Part A at 65 even if you are working, because it has no premium and covers hospital stays.

When you leave your job or your employer coverage ends, you have eight months to enroll in Part B without penalty. This eight-month window is your Special Enrollment Period. You must enroll within this window or face late penalties. Keep your termination letter or final pay stub as proof that your coverage ended — Medicare will ask for it.

If you are self-employed or own a business, you do not have employer coverage, so your regular seven-month window applies. The fact that you are still working does not extend it.

How to enroll during your window

You can enroll through three routes: online at Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office. Online enrollment through Medicare.gov is the fastest — you can complete it in 15 minutes if you have your Social Security number and birth date ready. The phone line has wait times, especially in the first and last weeks of your window.

You do not need to bring documents to enroll, but you should have your Social Security number, date of birth, and citizenship or immigration status information available. If you are enrolling in Part D at the same time, have a list of your current medications ready so you can compare plans that cover them.

If you miss your initial window but still have employer coverage, enroll during your Special Enrollment Period using the same three routes. Bring proof that your coverage ended — a termination letter, final pay stub, or COBRA notice — when you call or visit in person.

Part A versus Part B enrollment timing

Part A (hospital insurance) and Part B (medical insurance) have the same enrollment window, but they work differently if you miss it. Part A has no monthly premium, so there is no late penalty for delaying it. You should enroll in Part A at 65 even if you plan to stay on your employer plan, because it costs nothing and covers hospital stays your employer plan might not.

Part B has a monthly premium and a late penalty, so missing your window costs real money. If you are working and covered by an employer plan, you can delay Part B without penalty. But you must enroll in Part B within eight months of losing that coverage or face penalties.

Part D (drug coverage) is separate from Part A and Part B. You enroll in Part D during the same seven-month window as Part B, but you can also enroll during the Annual Enrollment Period (October 15 to December 7 each year). If you miss both windows and do not have creditable coverage, you pay a 1 percent monthly penalty for life.

Special situations that change your enrollment window

If you are a federal employee, you may have different rules. Federal employees can delay Part B enrollment while covered by the Federal Employees Health Benefits Program (FEHB) without penalty. When you retire or lose FEHB coverage, you have a Special Enrollment Period to enroll in Part B.

If you are a veteran, the Veterans Health Administration counts as creditable coverage for Part B purposes. You can delay Part B enrollment without penalty as long as you are using VA coverage. When you stop using VA coverage, you have eight months to enroll in Part B.

If you are on TRICARE (military family coverage), it counts as creditable coverage for both Part B and Part D. You can delay both without penalty while on TRICARE. When TRICARE ends, you have eight months to enroll in Part B and 63 days to enroll in Part D without penalty.

If you are not a U.S. citizen but are a lawful permanent resident or have a valid visa, you can enroll in Medicare at 65. Your enrollment window is the same as for citizens. Bring your immigration documents when you enroll.

What to do if you missed your window

If you missed your initial seven-month window and do not have employer coverage, you can still enroll, but you will pay a late penalty. Enroll as soon as you realize you missed the window — the penalty grows with each month you wait. Contact Medicare at 1-800-MEDICARE or visit Medicare.gov to enroll now.

When you call, tell them you missed your initial window and ask whether you may have access to for a Special Enrollment Period. If you had creditable coverage during the time you were not enrolled, you may be able to avoid the penalty. Have proof of that coverage ready — a letter from your former plan, an employer benefits statement, or a TRICARE card.

If you do not have creditable coverage, enroll anyway. The penalty will be calculated from the month after your initial window ended, but it stops growing once you enroll. The sooner you enroll, the lower your total penalty will be.

Frequently Asked Questions

Can I enroll in Medicare before I turn 65?

No, your enrollment window opens three months before you turn 65, not before. If you turn 65 in September, you can enroll starting in June. You cannot enroll earlier, even if you want to.

What if I turn 65 but I am not ready to retire yet?

You can enroll in Part A at 65 without enrolling in Part B. Part A has no premium and covers hospital stays. If you have employer coverage, you can delay Part B until you retire or lose that coverage, then enroll within eight months without penalty.

Do I have to enroll in Part D at the same time as Part A and Part B?

No. You can enroll in Part D during your initial seven-month window, or you can wait and enroll during the Annual Enrollment Period (October 15 to December 7) each year. If you go without Part D coverage and do not have creditable drug coverage, you pay a 1 percent monthly penalty for life.

What if my birthday is on the first of the month?

Your enrollment window still opens three months before and closes three months after the month you turn 65. If your birthday is January 1, your window opens October 1 of the previous year and closes April 30 of the current year.

Can I change my Medicare plan after I enroll?

Yes, but only during specific times. You can change plans during the Annual Enrollment Period (October 15 to December 7). If you have a may have access to life event — such as losing employer coverage, moving to a new state, or losing Medicaid — you may have a Special Enrollment Period to change plans outside the annual window.