Medicare Initial Enrollment Period — In Plain Words

Short answer: The Initial Enrollment Period is the first chance to sign up for Medicare Part A and Part B. It lasts 7 months. It starts 3 months before the month you turn 65. It includes the month you turn 65. It ends 3 months after the month you turn 65.

General information only. This page explains, in plain words, what Medicare says on its own official pages and in its own official booklet. It does not say what any one person should do. It does not decide if a person qualifies. For facts about one person’s own case, use the official routes at the end of this page.

The 7 months, month by month

Medicare calls this first sign-up time the Initial Enrollment Period.

It is tied to the month you turn 65.

That is 7 months in all.

Medicare’s booklet says to sign up early to avoid a delay in coverage.

When coverage starts

Medicare says the start date depends on which month you sign up.

Coverage always starts on the first of the month.

Part B, and Part A that you pay a premium for:

Part A with no premium:

Medicare calls this premium-free Part A.

Your Part A coverage starts the month you turn 65.

If your birthday is on the first of the month, coverage starts the month before you turn 65.

Signing up for premium-free Part A later

Medicare says you can sign up for Part A any time after you turn 65.

Your Part A coverage starts 6 months back from when you sign up.

It can also start 6 months back from when you apply for benefits from Social Security, or from the Railroad Retirement Board.

Coverage can’t start earlier than the month you turned 65.

If you are already getting Social Security benefits

This part is separate from signing up yourself.

Medicare’s booklet says this:

If you are getting benefits from Social Security or the Railroad Retirement Board, in most cases you will automatically get Part A and Part B.

They start the first day of the month you turn 65.

If your birthday is on the first day of the month, Part A and Part B start the first day of the prior month.

The booklet says the “Welcome to Medicare” package is mailed about 3 months before your 65th birthday.

Your Medicare card comes in this package.

The booklet also says:

If you are not getting Social Security benefits

The booklet says some people need to sign up themselves.

If you aren’t getting Social Security or Railroad Retirement Board benefits, and you want Part A or Part B, you will need to sign up.

The booklet says Medicare won’t mail you any enrollment information in that case.

Late enrollment penalties, in Medicare’s own words

Medicare’s coverage-start page says:

If you miss your 7-month Initial Enrollment Period, you may have to wait to sign up. You may also pay a monthly late enrollment penalty for as long as you have Part B coverage.

The page also says the penalty goes up the longer you wait.

Medicare’s booklet states the Part B penalty this way:

The late enrollment penalty takes the standard premium amount and increases it by 10% for each full 12-month period that you could have had Part B, but didn’t.

The booklet also says, in most cases, if you don’t sign up for Part B when you’re first eligible, you will have to pay a late enrollment penalty for as long as you have Part B.

The booklet states a Part A penalty too, for people who have to buy Part A:

If you aren’t eligible for free Part A, and you don’t buy it when you’re first eligible, your monthly premium may go up 10%.

You will have to pay the higher premium for twice the number of years you could have had Part A, but didn’t sign up.

This page prints no premium amounts and no penalty amounts in dollars. Medicare’s pages and booklet are the source for amounts.

Working past 65: a separate topic

This topic is separate from the Initial Enrollment Period.

It is about a different sign-up time, called a Special Enrollment Period.

Medicare’s coverage-start page describes it for people who have or had health insurance through a job.

The job can be your job, your spouse’s job, or a family member’s job if you’re disabled.

For that job-based case, the page states:

The page also says: If you sign up for Part B while you or your spouse are still working, or within the first full month after employer coverage ends, you can ask to delay your Part B start date up to 3 months.

The page also says COBRA isn’t considered group health plan coverage.

It says getting COBRA doesn’t change when this Special Enrollment Period ends.

Medicare’s booklet adds:

This page does not cover the other Special Enrollment Period situations. Medicare’s coverage-start page lists them.

If the Initial Enrollment Period has ended

Medicare’s coverage-start page says:

After your Initial Enrollment Period ends, you can only sign up for Part B and premium-Part A during one of the other enrollment periods.

One of those is the General Enrollment Period.

You can sign up between January 1 and March 31 each year.

Your coverage starts the month after you sign up.

You might pay a monthly late enrollment penalty, if you don’t qualify for a Special Enrollment Period.

Where to check the facts for one person

This page gives general information only.

It does not give any one person’s dates, coverage, or costs.

Medicare’s booklet prints these routes:

Sources

Medicare.gov (Centers for Medicare & Medicaid Services) — “When does Medicare coverage start?” https://www.medicare.gov/basics/get-started-with-medicare/sign-up/when-does-medicare-coverage-start

Medicare.gov (Centers for Medicare & Medicaid Services) — “Joining a plan.” https://www.medicare.gov/basics/get-started-with-medicare/get-more-coverage/joining-a-plan

Centers for Medicare & Medicaid Services — “Enrolling in Medicare Part A & Part B” (CMS Product No. 11036, Revised January 2018). https://www.medicare.gov/publications/11036-enrolling-medicare-part-a-part-b.pdf

Checked November 2, 2026