When Medicare Coverage Begins: Enrollment Deadlines and Start Dates

Medicare starts the first day of the month you turn 65, or the month after you enroll, whichever is later

If you turn 65 on any day of the month, your coverage begins on the first day of that same month — not on your birthday. If you turn 65 on March 15, Medicare Part A and Part B start March 1. If you turn 65 on March 1, coverage still starts March 1. The exception is if you enroll after your 65th birthday: then coverage starts the first day of the month after you enroll.

You do not have to wait until you turn 65 to enroll. You can sign up starting three months before the month you turn 65. If you miss the window around your birthday, you can still enroll later, but your start date moves forward and you may pay a permanent penalty on your premiums.

Part A (hospital insurance) and Part B (medical insurance) follow the same start date. Part D (prescription drug coverage) and Medigap or Medicare Advantage plans may have different rules and start dates depending on when you enroll and which plan you choose.

Key Takeaways

Medicare Part A and Part B start on the first day of the month you turn 65, regardless of which day of the month your birthday falls on.
You can enroll up to three months before you turn 65, and coverage will still begin the first of the month you turn 65.
If you enroll after your 65th birthday has passed, coverage begins the first day of the month after you complete enrollment.
Delaying enrollment past your birthday window can result in a permanent increase to your Part B premium for as long as you have Medicare.
Part D and supplemental plans have their own enrollment periods and start dates that may not align with Part A and Part B.

The three-month enrollment window before your 65th birthday

You can enroll in Medicare starting three months before the month you turn 65. If you turn 65 in June, you can enroll beginning in March. This window gives you time to compare plans, gather documents, and complete enrollment without rushing.

Enrolling early does not change your start date — coverage still begins the first of the month you turn 65. The advantage is that you avoid the rush and reduce the chance of missing a important date. You enroll through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.

What happens if you enroll after your birthday

If your 65th birthday passes and you have not yet enrolled, you can still sign up. Your coverage will begin on the first day of the month after the month you enroll. If you turn 65 in June and do not enroll until August, your coverage starts September 1.

Late enrollment also triggers a permanent penalty. Your Part B premium increases by 10 percent for each full 12 months you delayed enrollment past your 65th birthday. This penalty stays with you for life, even if you switch plans later. The penalty applies only to Part B; Part A does not usually carry a late-enrollment penalty if you have worked and paid Medicare taxes for at least 10 years.

Part D and prescription drug coverage start dates

Part D (prescription drug coverage) does not automatically start with Part A and Part B. You must enroll in a Part D plan separately, and the start date depends on when you enroll. If you enroll in Part D during your initial enrollment period (the same three-month window as Part A and B), coverage starts January 1 of the following year, regardless of when you enroll within that window.

If you enroll in Part D after your initial period ends, your coverage starts the first of the month after you enroll, and you may face a permanent penalty on your premiums. The penalty is 1 percent of the national average Part D premium for each month you delayed, rounded to the nearest dollar.

Medicare Advantage and Medigap plan start dates

If you choose a Medicare Advantage plan (Part C) instead of Original Medicare, your coverage typically starts January 1 of the year you enroll, even if you enroll in October or November. Some plans may allow enrollment outside the annual period if you have a may have access to life event, such as losing employer coverage or moving to a new service area.

Medigap (supplemental insurance) plans do not have a set start date tied to your Medicare enrollment. Coverage begins on the date your Medigap policy becomes effective, which the insurance company sets. This is usually the first of the month after you enroll, but it can vary by insurer and state. You have the strongest protections if you enroll in Medigap within six months of turning 65 and enrolling in Part B.

Special cases: disability and end-stage renal disease

If you are under 65 and receive Social Security Disability Insurance (SSDI) for at least 24 months, you become may be able to access for Medicare. Your coverage starts the 25th month of your disability benefit. You do not need to enroll; Medicare begins automatically.

If you have end-stage renal disease (ESRD) and need dialysis or a kidney transplant, you may be may be able to access for Medicare regardless of age. Coverage typically starts the first day of the month you begin dialysis or the month of your transplant. You should contact Social Security or your dialysis center to confirm your start date.

Frequently Asked Questions

Does my Medicare start on my birthday or the first of the month?

Medicare starts on the first day of the month you turn 65, not on your birthday itself. If you turn 65 on any date in March, your coverage begins March 1. If you enroll after your birthday, coverage starts the first day of the month after you enroll.

What if I turn 65 on the first day of the month?

Your Medicare still starts on the first of that month. There is no difference in timing whether you turn 65 on the 1st or the 31st — coverage always begins on the first day of your 65th birthday month if you enroll on time.

Can I delay Medicare and start it later?

You can delay enrollment, but delaying past your 65th birthday triggers a permanent penalty on Part B premiums. Part A does not usually have a penalty if you have worked and paid Medicare taxes for at least 10 years. Part D carries a 1 percent monthly penalty for each month you delay.

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

No. If you enroll in Part D during your initial enrollment period, coverage starts January 1 of the following year. If you enroll after that period, coverage starts the first of the month after you enroll. This may be months after your Part A and B start date.

What if I am still working at 65 — do I have to enroll in Medicare?

If you or your spouse are still working and have employer health coverage, you may be able to delay Medicare enrollment without penalty. You must have coverage through an employer with at least 20 employees. Contact your employer's benefits office and Medicare to confirm your situation before your 65th birthday.

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.