Medicare coverage begins the first day of the month you turn 65, or the first day of the month after you sign up, whichever is later

If you turn 65 on any day of the month, your Part A (hospital insurance) and Part B (medical insurance) coverage starts on the first day of that month—not on your birthday itself. For example, if you turn 65 on March 15, your coverage begins March 1. If you turn 65 on March 1, coverage also begins March 1.

If you sign up after your 65th birthday, your coverage starts on the first day of the month after you sign up. This delay is why signing up during your initial enrollment period matters: you avoid gaps in coverage and potential late penalties.

Key Takeaways

  • Part A and Part B coverage begins on the first day of the month you turn 65, regardless of which day of the month your birthday falls on.
  • If you sign up after turning 65, coverage starts the first day of the month following your sign-up date, which can delay your protection by weeks or months.
  • Your initial enrollment period runs three months before, the month of, and three months after you turn 65—signing up during this window avoids late penalties.
  • Part D (prescription drug) coverage and Medigap policies follow different start dates depending on when you enroll and which plan you choose.
  • You must be a U.S. citizen or permanent resident and have lived in the United States for at least five consecutive years to be covered.

How the first day of the month rule works

Medicare uses the first day of the calendar month as the standard start date for all new beneficiaries. This means the exact date you turn 65 does not matter—only the month matters. If your birthday is January 31, your coverage still begins January 1. If your birthday is January 2, your coverage also begins January 1.

The only exception is if you sign up after your 65th birthday. In that case, your coverage starts on the first day of the month after you complete your sign-up. If you turn 65 on June 15 but do not sign up until August 10, your coverage begins September 1.

Your initial enrollment period and why timing matters

Your initial enrollment period is a seven-month window: three months before you turn 65, the month you turn 65, and three months after you turn 65. If you sign up during this window, you avoid late penalties on Part B and Part D coverage.

If you miss this window and sign up later, you may owe a permanent penalty on your Part B premium (10 percent more per year for each year you delayed) and a permanent penalty on Part D (1 percent more per month for each month you delayed). These penalties stay with you for life, so signing up on time saves money over decades.

You can sign up through Medicare.gov, by calling 1-800-MEDICARE, or by visiting your local Social Security office. The Social Security Administration handles Medicare enrollment for most people.

Part A and Part B start dates

Part A (hospital insurance) and Part B (medical insurance) follow the same start date rule: the first day of the month you turn 65, or the first day of the month after you sign up if you enroll later. Most people are automatically enrolled in Part A when they turn 65 if they are already receiving Social Security benefits. If you are not yet receiving Social Security, you must sign up for Medicare separately.

Part B is not automatic—you must choose to enroll. If you do not sign up during your initial enrollment period and you do not have other health coverage (such as employer coverage), you will face a late penalty when you do enroll. The penalty applies to your monthly premium and is permanent.

Part D and Medigap coverage start dates

Part D (prescription drug coverage) and Medigap (supplemental insurance) have different rules than Part A and Part B. Part D coverage typically begins on the first day of the month after you enroll, but the exact date depends on which plan you choose and when you sign up. Some plans may have different effective dates, so check your plan documents.

Medigap policies also vary by plan and insurer. Some Medigap plans begin on the first day of the month you enroll; others may have a waiting period. If you enroll in Medigap during your initial enrollment period (which runs six months from when Part B starts), you have a may provide right to buy any Medigap plan in your state without medical underwriting. After that window closes, insurers can deny you or charge more based on your health history.

What happens between your birthday and your coverage start date

If your birthday is not the first of the month, there is a gap between your 65th birthday and when your coverage actually begins. During this gap, you are responsible for any medical costs. This is why having other coverage—such as employer health insurance or COBRA—during this time is important.

If you are still working and your employer offers health insurance, you can keep that coverage while you wait for Medicare to start. You do not have to enroll in Medicare when ready if you have employer coverage, though you will need to sign up eventually to avoid penalties.

Frequently Asked Questions

If I turn 65 on the 15th of the month, does my coverage start on the 1st or the 15th?

Your coverage starts on the 1st of that month, not on your birthday. Medicare always uses the first day of the calendar month as the start date for people turning 65. So if you turn 65 on March 15, your Part A and Part B coverage begins March 1.

What if I sign up for Medicare after I turn 65?

Your coverage will begin on the first day of the month after you sign up. If you sign up on July 20, your coverage starts August 1. The longer you wait after your initial enrollment period, the higher your late penalties will be.

Can I delay Medicare if I am still working?

Yes, if your employer has 20 or more employees and offers health insurance. You can delay Part B enrollment without penalty as long as you are covered by your employer plan. However, you must enroll in Part B within eight months of leaving your job or losing your employer coverage to avoid penalties.

Does my Part D prescription drug coverage start on the same date as Part A and Part B?

Not necessarily. Part D coverage typically begins the first day of the month after you enroll, but this varies by plan. Check your plan documents or contact your insurance company to confirm your exact start date. If you miss your initial enrollment period for Part D, you will face a permanent late penalty.

What if I am not a U.S. citizen—can I get Medicare?

You must be a U.S. citizen or permanent resident and have lived in the United States for at least five consecutive years to be covered by Medicare. If you meet these requirements, your coverage start date follows the same rules as for citizens.