When do I actually have to sign up for Medicare?

Your first Medicare signup window is your Initial Enrollment Period (IEP), the 7 months built around your 65th birthday. If you miss the wrong deadline, you can face permanent Part B or Part D penalties, and you can also lose the easiest time to buy Medigap without health questions.

Revised: 8/17/26
Jason Baar
Fee-Only Medicare Advisor
NPN #2033715

Start with your Initial Enrollment Period

Your Initial Enrollment Period, or IEP, is your first Medicare signup window. It lasts 7 months: the 3 months before your 65th birthday month, your birthday month, and the 3 months after.

During this window, you can sign up for Part A, hospital coverage; Part B, medical coverage; and Part D, drug coverage. If you sign up during this window, you avoid the standard late enrollment penalties.

If you are already collecting Social Security when you turn age 65, Medicare usually enrolls you in Parts A and B automatically and mails your card. If you are not collecting Social Security yet, you sign up through Social Security, either online or by phone. You do not sign up through Medicare itself.

Your start date depends on when you enroll. If you enroll before your birthday month, coverage begins the first day of your birthday month. If your birthday is on the 1st of the month, it begins the first day of the month before. If you enroll during or after your birthday month, coverage begins the first day of the month after you enroll.

A 2023 rule change fixed an old problem. During the IEP, Medicare coverage now never starts later than the month after enrollment.

The quiet HSA rule

Premium-free Part A can start retroactively if you take it after your 65th birthday. It can go back up to 6 months, but never earlier than the month you turned age 65.

That matters if you are still contributing to a Health Savings Account, or HSA. Once Part A is retroactive, those retroactive months count as Medicare months. HSA contributions for those months can become disallowed after the fact.

This is one of those rules that does not feel like a Medicare deadline until it causes a tax problem.

The two permanent late penalties

There are two Medicare late penalties that can follow you for life.

Part B has a permanent penalty if you delay without a valid reason. The penalty is 10% for each full 12 months of delay. The standard 2026 Part B premium is $202.90 per month, according to the 2026 Medicare premium tables. A two-year delay raises that to $243.48 per month, permanently.

Part D, drug coverage, has its own permanent penalty. It is 1% per month of delay, multiplied by the national base beneficiary premium. For 2026, that base premium is $38.99, according to the 2026 Medicare premium tables. A 24-month delay is about $9.36 per month. A 48-month delay is about $18.72 per month. The amount is added to your monthly premium for as long as you are on Medicare.

The Part D penalty starts after a continuous gap of 63 days or more without Part D or other creditable drug coverage. Creditable coverage means drug coverage that Medicare considers at least as good as standard Part D coverage.

The common mistake is easy to understand: someone takes no medications at age 65, skips Part D, and plans to buy it later if prescriptions show up. Later, the plan is available, but the penalty is permanent. Even the cheapest Part D plan during the IEP can close that door.

The Medigap deadline people miss

Medigap is the private supplement that pays your share of Original Medicare's costs.

The Medigap Open Enrollment Period is not the same as the Medicare IEP. It lasts 6 months and starts the first month you are both age 65 or older and enrolled in Part B.

This timing matters. If you delay Part B because you have current work coverage, your Medigap window waits. It does not start just because you turned age 65.

Inside that 6-month window, Medigap insurers cannot price you based on health history or decline you because of health history. A pre-existing condition wait of up to 6 months can apply in some cases, only for conditions treated or diagnosed in the prior 6 months, and it can be waived with qualifying prior coverage.

After the window closes, most states allow Medigap insurers to use health underwriting if you buy or switch later. That can mean a higher price, exclusions, or a no.

A few states have their own rules. A few federal guaranteed-issue events create narrow 63-day windows. None of those is as broad as the one-time 6-month Medigap Open Enrollment Period.

The deadline on TV is not your first deadline

The Annual Election Period, or AEP, runs October 15 through December 7 each year. This is the deadline most people see in Medicare ads.

During AEP, you can join, change, or drop a Medicare Advantage plan or Part D plan. Changes take effect January 1. If you do nothing, your current plan usually renews.

Your plan must send an Annual Notice of Change by September 30 each year. Read it before AEP. It tells you what is changing for the next year, including premiums, drug coverage, pharmacy rules, and costs, and sometimes network information.

AEP matters every year. It is just not the deadline that starts Medicare.

Other windows can matter later

The Medicare Advantage Open Enrollment Period, or MA-OEP, runs January 1 through March 31. It is only for people already on a Medicare Advantage plan. During this window, you can make one election: switch to another Medicare Advantage plan or return to Original Medicare, with the option to add a standalone Part D plan.

There is also a 5-star Special Enrollment Period from December 8 through November 30. It allows one switch into a 5-star-rated Medicare Advantage or Part D plan if one is available in your area.

If you delay Part B because you have coverage from current employment, you may get an 8-month Part B Special Enrollment Period after the job or employer coverage ends, whichever comes first. COBRA and retiree coverage do not count as current employer group coverage for this rule. Medicare says it plainly: "COBRA isn't considered group health plan coverage. Getting COBRA doesn't change when this Special Enrollment Period ends."

There is also a 12-month Medicare Advantage trial right. If you join a Medicare Advantage plan when first eligible at age 65, you have 12 months to return to Original Medicare and buy Medigap without health questions. After month 12, that right quietly expires.

The mail is not the deadline

Most of the mail around your 65th birthday is marketing.

Insurance companies can buy lists of people in a ZIP code who are turning age 65. The envelopes often sound urgent because they are trying to get your attention. That does not mean the date in the letter is your Medicare deadline.

Use your actual Medicare windows, not the mail pile, to decide what needs action.

For the rest of the turning-65 Medicare topics, visit the Free Medicare Guides library.