The Three Times You Can Enroll in Part B

You can sign up for Medicare Part B during three separate enrollment windows, and which one applies to you depends on when you turn 65 and whether you have coverage through an employer. Missing your window can mean paying a permanent penalty on your Part B premium, so the timing matters.

Your main enrollment period is the Initial Enrollment Period (IEP), which runs for seven months: three months before the month you turn 65, the month you turn 65, and three months after. If you sign up during this window, your coverage starts the first day of the month you turn 65 (or the month after, depending on when in the month you enroll). This is the easiest path and the one that avoids penalties.

If you miss your IEP, you can sign up during the General Enrollment Period (GEP), which runs January 1 through March 31 each year. Coverage would start July 1 of that year. However, signing up late means you will pay a permanent 10 percent increase on your Part B premium for each full year you went without coverage after your IEP ended.

The third window is the Special Enrollment Period (SEP), which applies only if you or your spouse had employer coverage when you turned 65. If you were covered through an employer plan (yours or your spouse's), you can sign up for Part B within eight months of losing that coverage without penalty, even if your IEP has passed. This is the exception that protects people who delayed Part B because they were still working.

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, with no penalty if you enroll during this time.
  • If you miss your Initial Enrollment Period and do not have employer coverage, you can still sign up during the General Enrollment Period (January 1 through March 31), but you will pay a permanent 10 percent premium increase.
  • If you had employer health insurance when you turned 65, you have eight months after losing that coverage to sign up for Part B without penalty, even if your Initial Enrollment Period has ended.
  • Part B coverage typically starts the first of the month you enroll (or the month after, depending on timing), except during General Enrollment, when it starts July 1.

How Your Employer Coverage Affects Your Signup Timeline

If you are still working at 65 and your employer offers health insurance, you do not have to sign up for Part B right away. You can delay Part B and stay on your employer plan instead, as long as your employer has 20 or more employees. This is called having creditable coverage, and it protects you from the late-enrollment penalty.

The key is that you must sign up for Part B within eight months of losing your employer coverage. That eight-month window is your Special Enrollment Period. If you wait longer than eight months, you will owe the 10 percent penalty for each year you were uninsured, and that penalty is permanent—it does not go away once you finally enroll.

Your employer should tell you when your coverage ends, but do not rely on that alone. Mark your calendar for eight months after your last day of coverage and plan to sign up before that date passes. If you are unsure whether your employer plan counts as creditable coverage, call your employer's benefits office or Medicare directly at 1-800-MEDICARE.

What Happens If You Miss Your Enrollment Window

If your Initial Enrollment Period has passed and you do not have employer coverage, you will pay a penalty. The penalty is 10 percent of the standard Part B premium amount for each full 12-month period you did not have Part B coverage after your IEP ended. That percentage is added to your premium permanently—even after you finally enroll, you will keep paying the higher amount for as long as you have Part B.

The only way to avoid this penalty is to enroll during the General Enrollment Period (January through March) or to prove you had creditable employer coverage when you turned 65. If you had employer coverage, you have eight months from the date it ended to sign up penalty-free. Keep documentation of when your coverage ended—a final pay stub, a letter from your employer, or a copy of your insurance card showing the termination date.

If you are already paying a penalty and want to know how much longer you will owe it, contact Medicare. The penalty continues as long as you have Part B, so there is no benefit to waiting further—enroll as soon as you can.

How to Sign Up During Your Enrollment Period

You can sign up for Part B in three ways: online through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office. Online is usually the fastest—you can complete the process in about 10 minutes if you have your Social Security number and Medicare number ready.

If you are signing up online, go to Medicare.gov, log in to your account (or create one), and look for the enrollment option. You will need to confirm your date of birth, citizenship status, and whether you have other health coverage. The system will show you your enrollment period and tell you when your coverage would start.

By phone, a Medicare representative can walk you through the same questions and enroll you on the spot. Wait times vary, but calling early in the morning or mid-week usually means shorter holds. If you go to a Social Security office, bring your Social Security card, proof of citizenship (passport or birth certificate), and proof of residency (utility bill or lease).

When Your Part B Coverage Actually Starts

The start date of your Part B coverage depends on when you enroll and which enrollment period you use. If you enroll during your Initial Enrollment Period, coverage typically starts on the first day of the month you turn 65. If you enroll after that but still within your IEP (the three months after your birthday month), coverage starts the first of the following month.

If you enroll during the General Enrollment Period (January through March), your coverage does not start until July 1 of that year, no matter when in January, February, or March you sign up. This is a significant gap, so if you are uninsured and need coverage sooner, look into whether you may have access to for a Special Enrollment Period through employer coverage or a life event like losing other insurance.

Once your Part B coverage starts, you will receive your Medicare card in the mail. It usually arrives within two weeks. If you need to see your coverage details before the card arrives, you can check your account on Medicare.gov or call 1-800-MEDICARE.

Special Cases: Delayed Retirement and Non-Citizens

If you delay claiming Social Security past age 65, you can still sign up for Part B at 65 without claiming retirement benefits. Your enrollment period is the same seven-month window. Some people delay Social Security to increase their benefit amount, but Part B enrollment is separate and should not be delayed just because you are delaying retirement.

If you are not a U.S. citizen, you can still sign up for Part B if you have been a permanent resident for at least five years and are at least 65 years old. Your enrollment period is the same as for citizens. You will need to provide proof of residency and your green card or other immigration documents when you enroll.

If you are a federal employee or railroad retiree, your enrollment rules may differ slightly. Federal employees have their own health insurance program and should contact their agency's benefits office before turning 65. Railroad retirees should contact the Railroad Retirement Board. In both cases, you still have an enrollment period, but the timing and coordination with your other coverage may work differently.

Frequently Asked Questions

What if I turn 65 in the middle of the month—does my coverage start that month or the next?

If you enroll before the 15th of your birth month, coverage starts the first of that month. If you enroll on the 15th or later, coverage starts the first of the next month. If you are close to the 15th, ask the Medicare representative when you call or enroll online—they can tell you exactly which month your coverage will begin based on your enrollment date.

Can I sign up for Part B online if I do not have a Medicare account yet?

Yes. Go to Medicare.gov and select "Create an account" if you do not already have one. You will need your Social Security number, email address, and a password. Once your account is set up, you can enroll in Part B. The whole process takes about 15 minutes.

If I had employer coverage and lost it, how do I prove it to avoid the penalty?

Keep any documentation showing when your coverage ended: a final pay stub, a letter from your employer's benefits office, or your insurance card showing the termination date. When you enroll, tell Medicare you had creditable employer coverage and provide the end date. Medicare will verify it with your employer if needed.

What if I am already retired and missed my enrollment period years ago?

You can still enroll during the General Enrollment Period (January 1 through March 31), but you will owe the late-enrollment penalty. The penalty is 10 percent of the standard Part B premium for each year you went without coverage. Once you enroll, the penalty stays on your premium permanently, so there is no advantage to waiting longer.

Do I have to sign up for Part B if I have retiree health insurance from my former employer?

Not when ready, but you should check with your employer's benefits office about whether your retiree plan counts as creditable coverage. If it does, you can delay Part B and sign up within eight months of losing that retiree coverage without penalty. If it does not count as creditable, you should sign up for Part B during your Initial Enrollment Period to avoid the penalty.