Medicare enrollment periods and late-enrollment penalties

Medicare does not always start by itself at 65. Many people have to sign up, and the sign-up windows are specific. Missing one can mean a gap in coverage and a premium penalty that lasts for years. This article covers the main enrollment periods and how the penalties are calculated. For what each part of Medicare covers, see Medicare Parts A, B, C and D explained.

The Initial Enrollment Period

For most people, the first chance to enroll is the Initial Enrollment Period. It lasts seven months: it begins three months before the month a person turns 65 and ends three months after that month.

When coverage begins depends on when the person signs up:

• Signing up before the month of the 65th birthday means coverage starts that birthday month.
• Signing up in the birthday month or the three months after means Part B coverage starts the following month.

(For people born on the first day of a month, the dates shift one month earlier.)

Who is enrolled automatically

According to Medicare.gov, some people get Part A and Part B automatically. That generally includes people who began receiving Social Security benefits at least four months before turning 65. People who are not yet collecting Social Security at 65, which is common among those who are still working or are delaying their claim, generally need to sign up themselves through Social Security.

Delaying Part B while covered through current work

Part B has a monthly premium, so people who still have employer coverage often ask whether they can wait. Medicare.gov's page on working past 65 explains that a person with group health coverage based on their own or a spouse's current employment may generally delay Part B without a penalty.

When the work or the coverage ends, whichever comes first, an eight-month Special Enrollment Period begins. Signing up within that window avoids the penalty.

Several details are frequently misunderstood:

• COBRA does not count. COBRA is continuation coverage after employment ends. Medicare.gov states that the eight-month period runs from when the work or coverage ends, whether or not COBRA is chosen. Waiting for COBRA to run out can mean missing the window.
• Retiree coverage does not count. The end of retiree coverage does not create a Special Enrollment Period.
• Plan rules matter. Medicare.gov suggests asking the employer's benefits administrator whether the plan requires enrollment in Part A and Part B at 65. Some coverage pays less once a person is eligible for Medicare.
• Health savings accounts. Premium-free Part A can begin up to six months before the sign-up date, so Medicare.gov advises stopping HSA contributions six months before retiring or applying for Social Security benefits. See health savings accounts: the basics.
• Coverage that is not from a job follows different rules. That includes individual plans bought through the Marketplace. See health coverage if you retire before 65.

Other Special Enrollment Periods exist for particular circumstances, such as losing Medicaid or being affected by a declared disaster. The full list is on Medicare.gov's page on when coverage starts.

The General Enrollment Period

Someone who misses the Initial Enrollment Period and does not qualify for a Special Enrollment Period can sign up during the General Enrollment Period, which runs from January 1 through March 31 each year. Coverage starts the month after sign-up. A late-enrollment penalty may apply.

How the late-enrollment penalties work

Medicare.gov's page on late enrollment penalties describes three separate penalties.

Part B. The premium goes up 10% for each full 12-month period a person could have had Part B but did not. The penalty generally lasts as long as the person has Part B.

Using Medicare's own illustration: someone who waited two full years without qualifying for a Special Enrollment Period pays a 20% penalty. With the 2026 standard premium of $202.90, that adds $40.58, for a monthly premium of about $243.50. Because the penalty is a percentage, it rises when the standard premium rises.

Part D. A penalty may apply if, after the Initial Enrollment Period, a person goes 63 days or more in a row without Medicare drug coverage or other creditable drug coverage, meaning coverage that is similar in value to Part D. The penalty is 1% of the national base beneficiary premium ($38.99 in 2026) for each full month without coverage, added to the monthly premium for as long as the person has Medicare drug coverage. Fourteen months without coverage would mean a 14% penalty, or about $5.50 a month in 2026.

Part A. Most people get Part A without a premium and face no penalty. For those who have to buy Part A and do not do so when first eligible, the premium may be 10% higher for twice the number of years they delayed.

Yearly periods for changing plans

Enrolling in Parts A and B is separate from choosing how to receive the coverage. Medicare.gov's page on joining a plan lists the recurring windows:

Medigap has its own one-time window. The Medigap open enrollment period lasts six months, beginning the first month a person has Part B and is 65 or older. It does not repeat each year.

Signing up for Medicare and claiming Social Security are separate decisions. A person can enroll in Medicare at 65 and start Social Security retirement benefits earlier or later.

Questions worth asking before 65

• Is current health coverage based on active employment, and does the plan expect enrollment in Medicare at 65?
• If retiring, what date does employer coverage end, and when does the eight-month window close?
• Is current drug coverage creditable? The plan or benefits administrator can confirm whether it is.