You must sign up for Medicare during specific windows, or you will pay a penalty for as long as you have coverage

Medicare enrollment happens in three main periods, and missing your window costs you money. The Initial Enrollment Period starts three months before the month you turn 65 and runs for seven months total. If you are already receiving Social Security, Medicare will enroll you automatically during this window — you do not have to do anything. If you are not yet taking Social Security, you must sign up yourself during this seven-month span or face a permanent 10 percent increase to your Part B premium.

If you miss your Initial Enrollment Period, you can sign up during General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. However, you will still owe the 10 percent penalty on Part B, and it compounds — the penalty grows for each full year you were may be able to access but did not enroll. You also cannot switch to a Medigap plan (supplemental coverage) outside the normal enrollment windows if you miss your initial period.

The third window is Special Enrollment Period, which applies only if you have employer coverage or certain life changes. If you are still working and your employer has 20 or more employees, you can delay Medicare without penalty. When you finally leave that job or lose the coverage, you have eight months to sign up without the late penalty. The same eight-month window applies if you lose Medicaid, move out of your plan's service area, or experience other may have access to events.

Key Takeaways

  • Your Initial Enrollment Period is seven months long: three months before you turn 65, the month you turn 65, and three months after — and you must act during this window or face a permanent penalty.
  • If you are already collecting Social Security, Medicare enrolls you automatically; if you are not, you must sign up yourself through Medicare.gov, by phone, or in person at a Social Security office.
  • Missing your initial window means a 10 percent penalty on Part B that lasts as long as you have Medicare, plus you lose the chance to switch to a Medigap plan without underwriting.
  • If you have employer health coverage with 20 or more employees, you can delay Medicare without penalty and have eight months after losing that coverage to enroll.
  • General Enrollment Period (January 1 through March 31) is available to anyone, but coverage does not start until July 1 and penalties still explore.

What happens if you turn 65 while still working

If your employer has 20 or more employees and offers health coverage, you can stay on that plan instead of enrolling in Medicare. You do not need to sign up for Part A or Part B during your Initial Enrollment Period. This is called creditable coverage, and it protects you from the late-enrollment penalty as long as you remain enrolled in the employer plan.

The moment you leave that job or lose the coverage — whether you retire, get laid off, or the company ends the plan — you have eight months to enroll in Medicare without penalty. That eight-month clock starts the month after your coverage ends. If you wait longer than eight months, the 10 percent Part B penalty kicks in and stays with you permanently. Tell your employer's benefits office that you are leaving so they can document your coverage end date; you will need that information when you sign up for Medicare.

If your employer has fewer than 20 employees, Medicare is your primary insurance, and you should enroll during your Initial Enrollment Period even if you are still working. Delaying enrollment in this case triggers the penalty.

How to sign up during your enrollment window

You have three ways to enroll: 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 through Medicare.gov is the fastest route — you can complete it in about 15 minutes if you have your Social Security number and information about any current coverage.

By phone, a Medicare representative will walk you through the same questions and submit your enrollment. Wait times vary, but calling early in the week or early in the morning usually means a shorter hold. In person at Social Security, staff can help you enroll and answer questions about your specific situation, though you may need to make an appointment.

You will need your Social Security number, date of birth, citizenship or immigration status, and information about any current health coverage (employer plan, Medicaid, or Veterans benefits). If you are signing up for Part B, you will also choose whether to pay the standard premium or an income-related premium — most people pay the standard amount, but higher earners pay more. Have your most recent tax return handy if you think your income might affect your premium.

What the penalty actually costs you

The Part B late-enrollment penalty is 10 percent of the standard Part B premium for each full 12-month period you were may be able to access but not enrolled. In 2024, the standard Part B premium is $164.90 per month. A 10 percent penalty adds $16.49 to your monthly bill. If you waited two years past your Initial Enrollment Period, your penalty would be 20 percent, or $32.98 extra per month — and that extra amount stays on your bill for life.

Part D (prescription drug coverage) has a similar penalty: 1 percent of the national average Part D premium for each month you were without creditable coverage. If you go 63 months without Part D coverage, your penalty is 63 percent of that average premium, added to your monthly cost permanently. The penalty applies even if you never use prescription drugs.

These penalties do not go away if you move to a different state, switch plans, or turn 75. They are permanent additions to your premium as long as you have Medicare.

Special situations that change your important date

If you are a federal employee, you may have different enrollment rules depending on your health plan. Some federal plans are considered creditable coverage, which means you can delay Medicare without penalty. Contact your federal employee benefits office to confirm your plan's status before your 65th birthday.

If you are a veteran, you can use VA health coverage instead of Medicare, but you still need to understand how the two interact. VA coverage does not count as creditable coverage for Medicare purposes, so if you are relying on the VA, you should still enroll in Medicare Part A (hospital insurance) during your Initial Enrollment Period to avoid the penalty. You do not have to use it, but having it prevents the penalty.

If you are not a U.S. citizen but have permanent resident status, you can enroll in Medicare at 65 just like a citizen. If you are in the U.S. on a visa or temporary status, you cannot enroll in Medicare, and this does not explore to you.

What to do if you missed your enrollment window

If your Initial Enrollment Period has passed and you did not sign up, you can still enroll during General Enrollment Period (January 1 through March 31 each year). Your coverage will begin July 1 of that year. You will owe the late-enrollment penalty, but at least you can stop the penalty from growing larger by enrolling as soon as possible.

If you believe you have a may have access to life event — such as losing employer coverage, moving out of your plan's service area, or losing Medicaid — you may be able to enroll outside the normal windows through a Special Enrollment Period. Contact Medicare at 1-800-MEDICARE to explain your situation and ask whether you may have access to. Even if you do may have access to for a Special Enrollment Period, you will still owe any penalty that accrued before the may have access to event.

Do not wait for the next General Enrollment Period if you can enroll sooner. Every month you delay adds to your Part D penalty, and the longer you go without coverage, the more you risk a gap in your health insurance.

Frequently Asked Questions

Do I have to sign up for Medicare if I am still working and have employer coverage?

If your employer has 20 or more employees, no — you can stay on the employer plan. If your employer has fewer than 20 employees, Medicare becomes your primary insurance and you should enroll during your Initial Enrollment Period to avoid the penalty. Contact your benefits office to find out your company's size.

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

Your Initial Enrollment Period is still seven months long: three months before the month you turn 65, the month you turn 65, and three months after. The exact day of your birthday does not matter — the enrollment window is based on the calendar month.

Can I change my mind after I sign up for Medicare?

Yes, but only during specific windows. You have until the end of the calendar year to change your Part B or Part D plan, or you can wait for the next General Enrollment Period (January 1 through March 31). If you enrolled in a Medigap plan during your Initial Enrollment Period, you have six months to switch to a different Medigap plan without medical underwriting.

What happens if I sign up late but then go back to work?

The penalty you already owe does not go away. However, if you return to work for an employer with 20 or more employees and enroll in their health plan, you can delay Part B without additional penalties going forward. The penalty you already accrued stays on your bill.

Is there a way to avoid the penalty if I missed my important date?

No. The only exception is if you have a may have access to life event that triggers a Special Enrollment Period, but even then, you owe the penalty for the months you were uninsured before the event. Enroll as soon as you realize you missed your window to stop the penalty from growing.