When to Sign Up for Medicare: Enrollment Periods Explained

Most people become eligible for Medicare around age 65. Signing up during the right window helps you avoid gaps in coverage and, in some situations, lifetime late enrollment penalties on Part B and Part D premiums.

The right time to enroll depends on whether you are turning 65, still working with employer coverage, or missed an earlier deadline. This guide summarizes the main sign-up paths in plain language. Rules can vary by situation — always confirm your personal timeline with official sources before making enrollment decisions.

For the majority of Americans, the best time to enroll in Part A (hospital insurance) and Part B (medical insurance) is during the Initial Enrollment Period — the seven-month window centered on your 65th birthday month.

If you already receive Social Security retirement benefits before 65, Medicare may enroll you automatically and mail your Medicare card about three months before your coverage begins. If you are not yet receiving Social Security, you generally need to apply actively through the Social Security Administration (SSA).

You can also choose how to receive your benefits after enrolling in Part A and Part B — for example, staying in Original Medicare with optional Part D and Medigap, or joining a Medicare Advantage plan. Those are separate decisions from when you sign up for Part A and Part B.

Initial Enrollment Period (IEP)

Your Initial Enrollment Period is usually a seven-month window that:

Starts three months before the month you turn 65
Includes your birthday month
Ends three months after your birthday month

Birthday on the 1st of the month: If your 65th birthday falls on the first day of a month, Medicare treats your enrollment timeline as if your birthday were the prior month. Your seven-month window shifts accordingly — a detail that catches many people off guard.

When coverage starts during your IEP

Your Part A and Part B coverage start date depends on which month within your IEP you sign up:

Enroll in the three months before your birthday month: Coverage typically begins on the first day of your birthday month.
Enroll during your birthday month: Coverage usually starts the first day of the following month.
Enroll in the three months after your birthday month: Coverage generally begins the first day of the month after you sign up.

Signing up early in your IEP (the three months before your birthday month) is the simplest way to avoid a gap if you are leaving employer coverage around age 65. For a step-by-step date calculator, see our guide on how to count your 7-month IEP.

General Enrollment Period (GEP)

If you miss your Initial Enrollment Period and do not qualify for a Special Enrollment Period, you may need to wait for the General Enrollment Period.

The GEP runs January 1 through March 31 each year. During this window you can sign up for Part B (and buy Part A if you do not qualify for premium-free Part A and missed your IEP).

Coverage timing: If you enroll during the GEP, coverage typically starts the first day of the month after you sign up — not retroactively.

Penalties: People who enroll during the GEP because they missed earlier deadlines may owe late enrollment penalties for Part B and, in some cases, Part A. Penalties can last as long as you have Medicare.

The GEP is a fallback — not the ideal path if you can enroll during your IEP or an SEP instead.

Special Enrollment Period (SEP)

A Special Enrollment Period lets you sign up for Part A and/or Part B outside the standard windows when a qualifying event applies — most often, having group health plan coverage based on current employment.

Working past 65 with employer coverage

If you (or your spouse) have health coverage through an employer or union based on current work, you may be able to delay Part B without penalty. The rules depend partly on employer size:

Large employers (generally 20 or more employees): You can often delay Part B while the group plan is primary. Many people still enroll in premium-free Part A at 65.
Small employers (generally fewer than 20 employees): Medicare is usually primary when you are 65+, so delaying Part B can leave you without proper primary coverage.

When employment or employer coverage ends, you typically have an eight-month SEP to enroll in Part A and/or Part B without a late penalty. The window starts the month after employment or group coverage ends — whichever comes first.

Important: COBRA continuation coverage, retiree health plans, and individual marketplace plans generally do not count as creditable employer coverage for delaying Part B. If you rely on one of those at 65, you may still need to enroll during your IEP.

For SEP rules, required forms, and Part D timing, see our guides on Medicare Special Enrollment Periods and turning 65 while still working.

Late enrollment: penalties to understand

Missing eligible sign-up windows without creditable coverage can trigger permanent surcharges:

Part B late enrollment penalty

If you do not enroll in Part B when first eligible and do not have qualifying coverage, Medicare may add a 10% surcharge to your Part B premium for each full 12-month period you could have had Part B but did not enroll. This penalty generally lasts for as long as you have Part B.

Part D late enrollment penalty

If you go 63 days or more without creditable prescription drug coverage after becoming eligible, you may owe a Part D late enrollment penalty. The calculation is based on how long you went without creditable coverage.

These penalties are why timing matters even if you feel healthy at 65. Planning ahead — especially if you work past 65 — helps you avoid surprises.

Turning 65 without qualifying employer coverage: Sign up during your Initial Enrollment Period (seven months around your birthday month). Coverage start depends on which month you enroll within that window.
Missed your IEP and no SEP applies: You may need the General Enrollment Period (January 1 – March 31). Coverage typically starts the month after you enroll.
Delayed because of active employer coverage: Use your Special Enrollment Period (generally eight months after employment or group coverage ends). Coverage usually starts the month after you enroll.

This overview is simplified. Your exact dates may differ — verify with SSA or Medicare.gov.

Most people apply for Medicare through the Social Security Administration:

Online: Create or use your my Social Security account and apply for Medicare benefits.
By phone: Call Social Security at 1-800-772-1213 (TTY 1-800-325-0778).
In person: Visit your local Social Security office.

If you need to document employer coverage for a Special Enrollment Period, SSA may ask for forms such as CMS-40B (Part B application) and CMS-L564 (employer coverage verification).

For a broader turning-65 roadmap — automatic enrollment, HSAs, and plan comparisons — see our Turning 65 Medicare guide.

Verify with official sources

Medicare enrollment rules change and individual circumstances vary. For the most current, authoritative information on when and how to sign up:

When to sign up for Medicare — Medicare.gov

You can also call 1-800-MEDICARE or contact your State Health Insurance Assistance Program (SHIP) for free, unbiased help.

Important reminder

This article is educational only. It does not list every plan available in your area and does not recommend specific carriers, products, or enrollment actions. We are not connected with or endorsed by the U.S. government or the federal Medicare program.

When to Sign Up for Medicare: Enrollment Periods Explained