File for Medicare Part B during your Initial Enrollment Period or during General Enrollment

Your Initial Enrollment Period is a seven-month window centered on the month you turn 65. It runs from three months before your 65th birthday through three months after. If you enroll during the three months before you turn 65, your coverage starts the month you turn 65. If you enroll in the month you turn 65 or the three months after, your coverage starts the following month.

If you miss your Initial Enrollment Period, you can file during General Enrollment, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. However, missing your Initial Enrollment Period triggers a late enrollment penalty — a permanent increase to your Part B premium that lasts as long as you have Medicare. The penalty is roughly 10 percent of the standard premium for each full year you could have had Part B but did not enroll.

You do not owe a penalty if you had creditable coverage (employer or union health insurance, TRICARE, or certain other plans) and enrolled within eight months of losing that coverage. This is called the Special Enrollment Period.

Key Takeaways

  • Your Initial Enrollment Period is seven months long, centered on your 65th birthday, and is the only time you can enroll without a permanent penalty.
  • Enrolling before you turn 65 means coverage starts at 65; enrolling after means a one-month delay.
  • If you miss your Initial Enrollment Period and had no creditable coverage, you can enroll during General Enrollment (January through March), but you will pay a higher premium for life.
  • If you lose employer or union coverage, you have eight months to enroll without penalty through a Special Enrollment Period.
  • You file through Social Security, Medicare.gov, or your local Social Security office — not through your doctor or hospital.

Why the timing matters: the penalty and when coverage begins

The late enrollment penalty exists because Medicare assumes people who delay enrollment are more expensive to insure. The penalty is not a one-time fee — it is a permanent percentage increase to your monthly premium. If you wait five years to enroll, you pay roughly 50 percent more than someone who enrolled on time, and you keep paying that extra amount every month for the rest of your life.

The other reason timing matters is when your coverage actually starts. If you are already 65 and working, or if you are turning 65 soon, the month you enroll determines the month coverage begins. Waiting even one month can mean a gap in coverage if you do not have another plan. Many people assume they can enroll anytime after 65 without consequence — that assumption costs them thousands of dollars over time.

Enrolling before you turn 65 if you are still working

If you are still working at 65 and your employer has 20 or more employees, you may not need Part B right away. You can delay enrollment without penalty as long as you enroll within eight months of retiring or losing that employer coverage. This is part of the Special Enrollment Period rule.

However, you must have actual employer coverage — not just be may be able to access for it. If your employer offers coverage but you declined it, you do not have creditable coverage and the penalty clock starts ticking. Check with your employer's benefits office about what counts as creditable coverage under Medicare rules; the definition is narrower than you might expect.

If you do enroll before you retire, your Part B coverage can start as early as the month you turn 65, even if you are still working. There is no rule against having both employer coverage and Medicare Part B at the same time.

What happens if you miss your Initial Enrollment Period

If you turn 65, do not enroll, and do not have creditable coverage, your next chance is General Enrollment from January 1 through March 31. You can enroll any year during this window. Your coverage will begin July 1 of that year.

The catch is the late enrollment penalty. If you were supposed to enroll at 65 but did not enroll until age 68, you owe a penalty for three years of non-enrollment. That penalty stays on your premium permanently. Some people think the penalty goes away after a few years — it does not.

There is one exception: if you can prove you did not know you needed to enroll and had no reasonable way to know, you may be able to request a waiver of the penalty. This is rare and requires documentation. Contact Social Security to ask whether your situation qualifies.

Special Enrollment Period: losing coverage and the eight-month window

If you have employer or union health insurance, TRICARE, or certain other forms of creditable coverage, and you lose that coverage, you have eight months to enroll in Part B without penalty. This eight-month clock starts the month your coverage ends.

You must enroll during this eight-month window. If you wait nine months, the penalty applies. When you do enroll, coverage typically begins the month after you file, but check with Social Security or Medicare to confirm the exact start date for your situation.

Keep documentation of when your coverage ended — a final pay stub, a letter from your employer, or a notice from your health plan. Medicare may ask for proof that you had creditable coverage and when it ended.

How to file: Social Security, Medicare.gov, or in person

You file for Part B through one of three routes. The easiest for most people is Medicare.gov — you can create an account, review your enrollment status, and file online. You will need your Social Security number and basic information about any current coverage.

You can also file through Social Security by calling 1-800-772-1213 (TTY 1-800-325-0778) or visiting your local Social Security office. Have your Social Security number and Medicare number (if you have one) ready. Processing by phone or in person usually takes the same amount of time as online filing.

If you are already receiving Social Security benefits, you may be enrolled in Part B automatically. Check your Social Security account or call to confirm your enrollment status before your Initial Enrollment Period ends.

Timing your enrollment to avoid gaps in coverage

If you are turning 65 and currently have health insurance through an employer, a spouse's employer, or the individual market, plan your Part B enrollment at least one month before your current coverage ends. This prevents a gap between when your old coverage stops and when Part B begins.

If you are already 65 and uninsured, enroll as soon as possible. Even if you have missed your Initial Enrollment Period, enrolling during the next General Enrollment window (January through March) is better than waiting longer and accumulating more penalty years.

Some people coordinate Part B enrollment with enrollment in Part D (prescription drug coverage) or a Medigap or Medicare Advantage plan. These have their own enrollment periods and important date. If you are making changes to any part of your Medicare coverage, file all changes together to avoid confusion.

Frequently Asked Questions

What if I turn 65 while still working and do not want Part B yet?

You can delay Part B without penalty if you have employer coverage with 20 or more employees and you enroll within eight months of retiring or losing that coverage. You must have actual coverage, not just be may be able to access for it. Confirm with your employer that your plan counts as creditable coverage under Medicare rules.

Can I enroll in Part B anytime during the year?

You can enroll during your Initial Enrollment Period (seven months centered on your 65th birthday) without penalty. After that, you can only enroll during General Enrollment (January 1 through March 31 each year), and you will owe a late penalty. A Special Enrollment Period applies if you lose creditable coverage.

How much is the late enrollment penalty?

The penalty is roughly 10 percent of the standard Part B premium for each full year you could have had Part B but did not enroll. The penalty is permanent and increases your monthly premium for life. The exact amount changes each year with the standard premium.

What if I do not remember when I lost my employer coverage?

Contact your former employer's benefits office or your old health plan for a letter stating when your coverage ended. You will need this documentation to prove you may have access to for the Special Enrollment Period. Social Security or Medicare can tell you whether the eight-month window is still open based on that date.

Do I have to file for Part B if I am already on Medicare Part A?

Part A and Part B are separate. You must file for Part B separately, even if you are already enrolled in Part A. If you are receiving Social Security benefits, you may be enrolled automatically, but check your account to confirm. If you are not automatically enrolled, file during your Initial Enrollment Period to avoid a penalty.