When You Must Enroll in Medicare Part B and What Happens If You Miss the Deadline

You have a limited window to enroll in Part B without paying a penalty for life

Medicare Part B covers doctor visits, outpatient care, and medical equipment. Unlike Part A (hospital insurance), which most people get automatically at 65, you must actively enroll in Part B. The enrollment window is seven months long: three months before the month you turn 65, the month you turn 65, and three months after. If you miss this window and do not have other health coverage, you will pay a permanent 10% increase on your Part B premium for every 12 months you delayed.

The penalty applies for as long as you have Medicare, so the cost of missing the important date compounds over years. Even if you delay enrollment intentionally, the penalty still applies unless you had creditable coverage — meaning health insurance through an employer, a spouse's employer, or certain other sources that was as good as or better than Medicare.

Key Takeaways

Your initial enrollment period is seven months: three months before you turn 65, the month you turn 65, and three months after.
If you miss this window and have no other health coverage, you will pay a permanent 10% increase on your Part B premium for every 12 months you were late.
You do not pay the penalty if you had creditable coverage through an employer or spouse's employer during the time you delayed.
You can enroll in Part B through Social Security, Medicare.gov, or by calling 1-800-MEDICARE, and enrollment takes effect the first of the month following approval.

Who must enroll and when

You must enroll in Part B when you turn 65, unless you are still working and covered by your employer's health plan. If you are covered through your own job or your spouse's job, you can delay Part B without penalty as long as the coverage lasts. Once that coverage ends — whether because you retire, leave the job, or the employer drops the plan — you have eight months to enroll in Part B without penalty. This is called the Special Enrollment Period.

If you are already receiving Social Security benefits when you turn 65, Medicare Part B enrollment happens automatically. You will receive a Medicare card in the mail about three months before your 65th birthday. If you are not yet receiving Social Security, you must enroll yourself.

How to enroll in Part B

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 at Medicare.gov is the fastest option if you have your Social Security number and a way to verify your identity. The phone line has wait times but staff can answer questions about your specific situation.

When you enroll, have your Social Security number and information about any current health coverage ready. Enrollment takes effect on the first day of the month after Medicare approves your request. If you enroll during your initial seven-month window, coverage typically begins the month you turn 65 or the month after, depending on when in the month you enroll.

What the permanent penalty costs

The Part B premium changes each year. For 2024, the standard premium is $164.90 per month, but your actual premium may be higher based on your income. If you enroll late, you pay an additional 10% for each full 12-month period you delayed. If you delayed for two years, you pay 20% more. If you delayed for five years, you pay 50% more. This increase stays on your premium permanently — it does not go away after a certain time.

The penalty applies only if you did not have creditable coverage. Creditable coverage includes health insurance through an employer, a union, COBRA, the Veterans Health Administration, or certain other sources. It does not include Medicaid, the Marketplace, or short-term plans. If you had any of these during your delay, you will not owe the penalty.

What happens if you miss your enrollment window

If you miss your initial seven-month window and do not have creditable coverage, you can still enroll in Part B, but the penalty applies when ready. You cannot avoid it by waiting longer. The sooner you enroll after missing the important date, the sooner you stop accumulating additional penalty months.

You can enroll during the General Enrollment Period, which runs from January 1 to March 31 each year. Coverage begins July 1 of that year. This means if you miss your initial window in June and do not enroll until the next General Enrollment Period in January, there will be a gap in coverage. During that gap, you are responsible for all doctor and outpatient costs.

Special situations that change your important date

If you are still working and covered by your employer's health plan at 65, do not enroll in Part B yet. Enroll within eight months of the date your coverage ends. If you miss this eight-month window, the standard penalty applies.

If you are a federal employee, railroad retiree, or covered under certain other government plans, your rules may differ. Contact your benefits office or call 1-800-MEDICARE to confirm your important date. If you are on disability and turn 65, your enrollment rules are the same as for anyone else — you have the same seven-month window.

Questions to ask your doctor or Social Security

Before you enroll, ask your current doctor whether they accept Medicare. Ask whether your prescriptions are covered under Part D (prescription drug coverage) and whether you need to enroll in Part D at the same time. If you are still working, ask your employer's benefits office whether your coverage counts as creditable coverage for Medicare purposes — this determines whether you can delay Part B without penalty.

If you are unsure whether you have creditable coverage, call 1-800-MEDICARE and ask to speak with someone about your specific situation. They can tell you whether your current plan qualifies and what your important date is.

Frequently Asked Questions

What if I turn 65 while still working?

You do not have to enroll in Part B while you are covered by your employer's health plan. Once you retire or lose that coverage, you have eight months to enroll without penalty. If you miss that eight-month window, the 10% permanent penalty applies.

Can I enroll in Part B after I turn 65 if I do not need it yet?

You can delay if you have creditable coverage, but if you do not have any other health insurance, you should enroll during your initial seven-month window to avoid the penalty. Even if you do not use Medicare right away, enrolling protects you from the penalty.

What if I was automatically enrolled in Part B but I do not want it?

You can decline Part B if you have creditable coverage through an employer or spouse's employer. Contact Social Security or Medicare to request removal. Keep documentation of your creditable coverage in case you need to prove it later.

Does the Part B penalty ever go away?

No. The 10% increase for each 12-month delay period stays on your premium for life. It does not expire after a certain number of years. This is why enrolling as soon as you become may be able to access, even if you do not plan to use Medicare when ready, is important.

What if I cannot afford the Part B premium?

You may be able to get help paying premiums through the Medicare Savings Program, which is run by your state. Contact your state Medicaid office or call 1-800-MEDICARE to learn whether you may have access to based on your income and resources.

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.