When You Can Sign Up for Medicare Part B

Part B enrollment windows depend on when you turn 65 and whether you have other health coverage

You can sign up for Medicare Part B during your Initial Enrollment Period, which runs for seven months centered on your 65th birthday month. This means you can enroll three months before the month you turn 65, during that month itself, and three months after. If you miss this window, you can still sign up during the General Enrollment Period (January 1 through March 31 each year), but you will face a permanent late penalty on your premiums unless you had may have access to coverage.

If you are already receiving Social Security benefits when you turn 65, Medicare Part B enrollment happens automatically. You do not need to take any action—Part B coverage starts the first day of the month you turn 65. If you are not yet receiving Social Security, you must sign up yourself during your Initial Enrollment Period, or you risk the penalty.

The rules change if you have employer health insurance through your own job or your spouse's job. You can delay Part B without penalty as long as you stay covered by that employer plan. Once you leave the job or lose the coverage, you have eight months to sign up for Part B without penalty. This is called your Special Enrollment Period.

Key Takeaways

Your Initial Enrollment Period is seven months long: three months before your 65th birthday month, the month itself, and three months after.
If you receive Social Security at 65, Part B enrolls automatically; if you do not receive it, you must sign up yourself or face a permanent premium penalty.
If you have employer health insurance through work, you can delay Part B without penalty and have eight months after losing that coverage to sign up.
Missing your enrollment window means signing up only during January through March each year, with a penalty added to your premium for life.

What happens if you miss your Initial Enrollment Period

If you do not sign up for Part B during your seven-month Initial Enrollment Period, you can only enroll during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage would not start until July 1 of that year, leaving you without Part B for months.

More importantly, you will pay a permanent late enrollment penalty for as long as you have Medicare Part B. The 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. If you waited two years to sign up, your penalty would be 20 percent added to your premium forever. This penalty does not go away if you move to a different state or change plans.

The only way to avoid this penalty after missing your Initial Enrollment Period is to have had creditable coverage—meaning health insurance that is at least as good as Medicare Part B—during the time you were not enrolled. Employer plans, TRICARE, and some other group health plans count as creditable coverage. You will need to show proof of that coverage when you sign up.

Signing up if you have employer health insurance

If you or your spouse are still working and covered by an employer health plan, you do not have to sign up for Part B at 65. You can keep the employer coverage and delay Part B without any penalty, even if you are already on Medicare Part A.

The key is that the coverage must be based on current employment—either your own job or your spouse's job. Retiree health plans, COBRA coverage, or plans you buy on your own do not count. Once you or your spouse leaves that job or the employer coverage ends, you have eight months to sign up for Part B. This eight-month window is your Special Enrollment Period, and it protects you from the late penalty.

You should sign up during this eight-month window even if you plan to stay on the employer plan for a while longer. The timing of when you sign up does not affect when your Part B coverage starts—you can sign up in month two of the eight-month window and still have coverage begin on the first day of the month after you lose the employer plan. Waiting until month eight is riskier because if you miss the important date by even one day, you lose the Special Enrollment Period and face the permanent penalty.

How to sign up during your enrollment period

You can sign up for Part B online through Medicare.gov, by phone at 1-800-MEDICARE (1-800-633-4227), or in person at your local Social Security office. Online enrollment is usually the fastest option—you can complete it in about 10 minutes if you have your Social Security number and Medicare card ready.

If you are signing up by phone, have your Social Security number, date of birth, and current mailing address available. The Social Security representative will confirm your enrollment period, check whether you have other coverage, and process your sign-up. The call typically takes 15 to 20 minutes.

If you are signing up in person, bring your Social Security card, proof of citizenship or legal residency (a passport or birth certificate works), and proof of your current address (a utility bill or lease). Social Security offices can get busy, so calling ahead to schedule an appointment is a good idea. You can find your local office at ssa.gov.

Part B coverage start dates and premium timing

When your Part B coverage starts depends on when you sign up. If you sign up during the first three months of your Initial Enrollment Period (before your birthday month), coverage starts the first day of the month you turn 65. If you sign up in your birthday month, coverage starts July 1 of that year. If you sign up in the three months after your birthday month, coverage starts the first day of the month after you sign up.

Your Part B premium is deducted from your Social Security check each month, or you receive a bill if you do not receive Social Security. The standard premium amount changes each year. If you have a higher income, you may pay an Income-Related Monthly Adjustment Amount (IRMAA) on top of the standard premium. This is based on your tax return from two years prior, so your first year on Part B may have a different premium than expected.

If you sign up during the General Enrollment Period (January through March) because you missed your Initial Enrollment Period, your coverage does not start until July 1, and your premium starts in July. You will not have Part B coverage during the months between when you turn 65 and July 1, so any doctor visits or hospital stays during that time are not covered by Medicare.

Special situations: working past 65 or losing coverage

If you are still working at 65 and covered by your employer's health plan, you do not have to sign up for Part A (hospital insurance) either. You can delay both Part A and Part B without penalty as long as the employer coverage continues. Once you retire or lose that coverage, you have eight months to sign up for both without penalty.

If you lose employer coverage before you turn 65, you have a different rule. You can sign up for Part B during a Special Enrollment Period that starts the month you lose coverage and lasts eight months. This is separate from your Initial Enrollment Period around your 65th birthday. If you turn 65 while you are in this eight-month window, the window extends to eight months from the date you lost coverage, not eight months from your birthday.

If you have TRICARE (military health coverage) or Veterans Affairs coverage, you also have special enrollment rules. TRICARE counts as creditable coverage, so you can delay Part B without penalty. VA coverage does not count as creditable, but VA beneficiaries can sign up for Part B during their Initial Enrollment Period without penalty even if they did not sign up right at 65.

Frequently Asked Questions

What if I turn 65 and I am not yet receiving Social Security?

You must sign up for Part B yourself during your seven-month Initial Enrollment Period. Part B does not enroll automatically unless you are already receiving Social Security benefits. Contact Medicare at 1-800-633-4227 or visit Medicare.gov to sign up. If you miss this window, you can only enroll during January through March each year, and you will owe a permanent late penalty.

Can I sign up for Part B before I turn 65?

Yes. Your Initial Enrollment Period starts three months before the month you turn 65, so you can sign up as early as then. Signing up early does not start your coverage early—it will still begin the first day of the month you turn 65 (if you sign up in the first three months of your enrollment period). Signing up early just ensures you do not miss the important date.

What if my employer says I do not have creditable coverage?

Ask your employer's benefits department for a written statement about your coverage. Bring this to Medicare when you sign up. If there is a dispute about whether your coverage was creditable, Medicare can review it. Do not assume your coverage does not count—many plans do may have access to, and the penalty is permanent if you are wrong.

Do I have to sign up for Part B if I have a Medicare Advantage plan?

Yes. Medicare Advantage plans (Part C) require you to have both Part A and Part B. You cannot have a Medicare Advantage plan without Part B. You must sign up for Part B during your Initial Enrollment Period, even if you plan to use a Medicare Advantage plan instead of Original Medicare.

Can I change my mind after I sign up for Part B?

You can drop Part B, but you will owe the late penalty if you drop it and sign up again later (unless you have a may have access to reason). If you sign up and then realize you made a mistake, you have a limited time to cancel. Contact Medicare when ready at 1-800-633-4227 to ask about your options—the sooner you call, the better.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.