Medicare Initial Enrollment Period: Your 7-Month Window and When Coverage Starts

Seven months. That's your Initial Enrollment Period for Medicare: the 3 months before the month you turn 65, your birthday month, and the 3 months after. Sign up in the first three and Part B starts the first day of your birthday month. Sign up in your birthday month or later and it starts the first of the following month. Miss all seven, and the next regular chance is the General Enrollment Period, January through March, with a penalty that can follow you for as long as you have Part B.

That second rule is newer than a lot of people realize. Before January 1, 2023, signing up late in the window could leave you waiting two or three months for coverage. 42 CFR 407.25 now says that if you enroll during the last 4 months of the window, coverage begins the month after you enroll. Older articles online may still describe the old delay, so check the date on anything you read.

Florida has a lot of people in this window at any given moment. 5,346,788 Floridians were 65 or older in mid-2025, 22.8% of the state, and roughly 320,000 more were 64.

Source: 42 CFR 407.14; U.S. Census Bureau, Vintage 2025 state population estimates by age (July 1, 2025); CMS, 2026 Medicare Parts A & B premiums and deductibles.

The 7-month window, month by month

The federal rule is short. 42 CFR 407.14 defines the Initial Enrollment Period as the 7-month period that begins 3 months before the month you first become eligible and ends 3 months after it. For most people the eligibility month is the month they turn 65. Section 407.25 then sets the start date, and Medicare.gov's When does Medicare coverage start page says the same thing in plain English: sign up before the month you turn 65 and coverage starts the month you turn 65; sign up in that month or during the 3 months after, and coverage starts the next month. Coverage always starts on the first of a month.

Here's how that plays out for one person. This is a hypothetical: say your birthday is June 15, 1962, so you turn 65 on June 15, 2027.

Source: 42 CFR 407.25(a)(2); Medicare.gov, When does Medicare coverage start. Dates are the rule applied to a hypothetical birthday; the gap column assumes you want Part B from your birthday month.

Read the last column again. The window is seven months long, but only the first three get you covered on day one of your birthday month. Every month you wait after that is a month on whatever coverage you had before, or on nothing. For someone retiring from a job with health insurance on their 65th birthday, the first three months are the ones that matter.

Premium-free Part A works a little differently. If you qualify for it, it starts the month you turn 65, and you can sign up for Part A any time after that; Medicare backdates it up to 6 months, but never earlier than the month you turned 65. The timing pressure is on Part B.

• Before 2023
• Since Jan 1, 2023

0 mo1 mo2 mo3 mo4 mo

MarAprMayJunJulAugSep

Source: 42 CFR 407.25(a)(1) and (a)(2), including the rule's own table for the pre-2023 schedule.

Show the numbers

	Before 2023	Since Jan 1, 2023
Mar	3 mo	3 mo
Apr	2 mo	2 mo
May	1 mo	1 mo
Jun	1 mo	1 mo
Jul	2 mo	1 mo
Aug	3 mo	1 mo
Sep	3 mo	1 mo

The left side of that chart is the same under both rules: sign up in March and you wait three months, but only because your birthday month hasn't arrived yet. The difference is all on the right. Under the old schedule, someone who signed up in the last month of the window waited until December. Now it's October 1. That's a real improvement, but it doesn't make late sign-up free. You still have months without Part B, and if you sign up after September 30 in this example, you've missed the window entirely.

Born on the 1st? Everything moves up a month

This one is easy to miss. Under Social Security's rules, 20 CFR 404.2(c)(4), you legally attain an age on the day before your birthday. If your birthday is June 1, you turn 65 for Medicare purposes on May 31, which puts your eligibility month in May.

Medicare.gov uses exactly that example: with a June 1 birthday, the Initial Enrollment Period runs February through August, and signing up in February, March or April gets you coverage starting May 1.

Source: Medicare.gov, When does Medicare coverage start (birthday on the first of the month); 20 CFR 404.2(c)(4); 42 CFR 407.25.

If you were born on the 1st, count from the month before your birthday. Florida's Department of Financial Services applies the same shift to Medigap: its consumer guide says that when a birthday falls on the first day of the month, Part B coverage and the Medicare supplement open enrollment period begin on the first day of the previous month.

Automatic enrollment: who has to act and who doesn't

Some people never have to sign up at all. According to Medicare.gov's How do I sign up for Medicare page, if you start getting Social Security or Railroad Retirement Board benefits at least 4 months before you turn 65, you get Part A and Part B automatically. Medicare mails a welcome package with your card 3 months before your coverage starts.

Automatic Part B isn't mandatory Part B. Under 42 CFR 407.17, Social Security has to tell you that you've been enrolled and give you until at least 2 months after the month the notice is mailed to decline it. That matters if you're still covered by a large employer plan and don't want to pay the Part B premium yet. Don't send back the card on reflex, though. Check the employer rules in the working section below first.

Everyone else has to act. If you're not collecting Social Security yet, you sign up through Social Security: online with a my Social Security account, by phone at 1-800-772-1213 (TTY 1-800-325-0778), or at a local office. Railroad workers go through the Railroad Retirement Board at 1-877-772-5772. Medicare.gov says the card arrives about 2 weeks after you sign up.

Three clocks start at 65, not one

The Initial Enrollment Period is the window for Part A and Part B. Two other deadlines start around the same time, and they don't run on the same schedule.

Part D and Medicare Advantage. 42 CFR 423.38(a)(3) makes your Part D initial enrollment period the same 7 months as your Part B window. Per Medicare.gov's Joining a plan page, you need either Part A or Part B to join a drug plan, and both to join a Medicare Advantage plan. If you ask to join before your Medicare starts, plan coverage starts the same day Medicare does; if you ask after, it starts the first of the month after the plan gets your request. If you join a Medicare Advantage plan during this window, you can switch to another one or go back to Original Medicare within your first 3 months of having Part A and Part B.

If you go 63 days or more in a row after this window without Part D or other creditable drug coverage, a Part D late enrollment penalty can apply. I walk through the math in how Medicare's late enrollment penalties are calculated.

Medigap. Under federal law you get a 6-month Medigap Open Enrollment Period that starts the first month you have Part B and are 65 or older. During those 6 months, an insurance company can't refuse to sell you any Medigap policy it offers and can't charge you more for health conditions. It happens once. After it closes, an insurer can use medical underwriting and turn you down. Florida's version is in s. 627.6741(1)(a)1, Florida Statutes, and Florida extends it to people under 65 who have Medicare because of a disability or end-stage renal disease and are enrolled in Part B. More detail on the state side is in Florida's Medigap rules.

Source: 42 CFR 407.14; 42 CFR 423.38(a); 42 CFR 422.62(a)(1); Medicare.gov, Joining a plan; Medicare.gov, Medigap: Get ready to buy; Medicare.gov, Avoid late enrollment penalties.

Take the June 15 example again. If Part B starts June 1, 2027, the Medigap open enrollment period runs June 1 through November 30, 2027. If the same person delays Part B because they're still working, the Medigap clock waits too: it starts when Part B does. Florida's Department of Financial Services says the same thing for Floridians who sign up for Part B later than 65, giving them 6 months from the Part B effective date.

Nobody has to buy Medigap. The point is to know when you have the guaranteed right to, because Florida law has no annual or birthday-based right to switch Medigap policies later without underwriting.

Still working at 65

If you or your spouse have health coverage through current employment, you don't have to take Part B during your Initial Enrollment Period. You get a Special Enrollment Period instead: per Medicare.gov, it lasts while you have that coverage and for 8 months after the job or the coverage ends, whichever happens first.

Who pays first is the real question. Per CMS's who pays first guide, if the employer has 20 or more employees, the group plan generally pays first and Medicare pays second. With fewer than 20 employees, Medicare generally pays first, which means the employer plan may expect you to have Part B. Ask the benefits office which applies before you decline Part B.

Three traps catch people here:

• COBRA and retiree coverage don't count. Medicare.gov says COBRA isn't group health plan coverage for this purpose, and having it doesn't extend the 8 months.
• HSAs. You can't contribute to a Health Savings Account once you have Medicare, and Part A can be backdated up to 6 months when you sign up later. Medicare.gov suggests stopping contributions at least 6 months before you apply.
• The Medigap window follows Part B. That helps you if you delay correctly. It doesn't help if you sign up for Part B while still working "just in case" and then don't buy Medigap until you retire. By then the 6 months may be gone.

The full picture, including the paperwork Social Security wants when you finally sign up, is in Medicare and employer coverage after 65.

What Part B costs, and what missing the window costs

For 2026, the standard Part B premium is $202.90 a month and the annual deductible is $283, according to the CMS 2026 fact sheet. Higher-income enrollees pay more, through an income-related adjustment. CMS hasn't published the 2027 amounts as of October 23, 2026; last year's announcement came on November 14. If you're turning 65 in 2027, budget with the 2026 numbers and expect them to change.

Miss your Initial Enrollment Period without a Special Enrollment Period and two things happen. First, you can only sign up during the General Enrollment Period, January 1 to March 31, with coverage starting the month after you sign up. Second, Part B can come with a late enrollment penalty: 10% of the standard premium for each full 12 months you could have had Part B and didn't, usually for as long as you have Part B. Medicare.gov's own example is someone 2 full years late paying 20% extra, $243.50 a month in 2026 instead of $202.90.

Source: CMS, 2026 Parts A & B premiums and deductibles; Medicare.gov, Avoid late enrollment penalties (20% example); Medicare.gov, When does Medicare coverage start.

What to do at 64 and a half

Here's the order I'd work in, starting about six months before your 65th birthday month.

Source: 42 CFR 407.25; Medicare.gov, How do I sign up for Medicare; Medicare.gov, When does Medicare coverage start; Medicare.gov, Joining a plan; Medicare.gov, Medigap.

For a Florida-specific overview of coverage options once your dates are settled, see Medicare in Florida, Part D in Florida and Medicare Supplement insurance in Florida. If you want a second set of eyes on your dates, SHINE, the Florida Department of Elder Affairs' counseling program, gives one-on-one Medicare help that's unbiased, confidential and doesn't cost anything: 1-800-96-ELDER (1-800-963-5337). Medicare itself is at 1-800-MEDICARE (1-800-633-4227, TTY 1-877-486-2048).

Initial Enrollment Period questions

How long is the Medicare Initial Enrollment Period?

Seven months: the 3 months before the month you turn 65, the month you turn 65, and the 3 months after.

When does Medicare coverage start if I sign up during my Initial Enrollment Period?

If you sign up before the month you turn 65, Part B starts the first day of your birthday month. If you sign up in your birthday month or the 3 months after, it starts the first of the following month.

What if my birthday is on the first of the month?

Your window starts 4 months before the month you turn 65 and ends 2 months after it, and coverage can start the first day of the month before your birthday month. A June 1 birthday gives a February to August window.

Am I enrolled in Medicare automatically at 65?

Only if you are getting Social Security or Railroad Retirement Board benefits at least 4 months before you turn 65. Otherwise you sign up through Social Security.

Is the Part D enrollment period the same as the Initial Enrollment Period?

Yes. Federal rules make your Part D initial enrollment period the same 7 months as your Part B window.

Federal Medicare rules, Florida law and your own coverage documents control what applies to you. Confirm your dates with Social Security, 1-800-MEDICARE, SHINE or a licensed agent, and talk to an attorney for legal questions.

Sources

1. eCFR: 42 CFR 407.14, Initial enrollment period (Part B)
2. eCFR: 42 CFR 407.25, Beginning of entitlement: individual enrollment
3. eCFR: 42 CFR 407.17, Automatic enrollment
4. eCFR: 42 CFR 423.38, Enrollment periods (Part D)
5. eCFR: 42 CFR 422.62, Election of coverage under an MA plan
6. eCFR: 42 CFR 422.68, Effective dates of coverage (Medicare Advantage)
7. eCFR: 20 CFR 404.2, General definitions (attainment of age)
8. Medicare.gov: When does Medicare coverage start?
9. Medicare.gov: How do I sign up for Medicare?
10. Medicare.gov: Joining a plan
11. Medicare.gov: Avoid late enrollment penalties
12. Medicare.gov: Medigap, Get ready to buy
13. CMS: Medicare and Other Health Benefits: Your Guide to Who Pays First (Feb 2026)
14. CMS: Medicare & You 2027 handbook
15. CMS: 2026 Medicare Parts A & B premiums and deductibles (Nov 14, 2025)
16. Florida Statutes s. 627.6741, Medicare supplement issuance and renewal
17. Florida Department of Financial Services: Medicare Supplement insurance overview
18. U.S. Census Bureau: Vintage 2025 state population estimates by single year of age
19. Florida SHINE program