When to Sign Up for Medicare: Key Deadlines That Matter

Medicare enrollment has specific windows and deadlines — and missing them can result in late enrollment penalties that follow you for years. This guide explains when to sign up, what the key periods are, and what to do if your situation is not straightforward.

The Initial Enrollment Period

When you first become eligible for Medicare at 65, you have a seven-month Initial Enrollment Period (IEP) to sign up. This window runs:

• Three months before the month you turn 65
• The month you turn 65
• Three months after the month you turn 65

If you sign up in the three months before your birthday month, your coverage starts on the first day of your birthday month. If you wait until your birthday month or after, your start date may be delayed. Signing up early — in the months before your birthday — avoids that gap.

If You Have Employer Coverage, Read This First

If you are still working at 65 and covered by an employer health plan (or your spouse's employer plan), you may be able to delay Part B without penalty — but only if the employer plan meets certain standards.

Do not assume you can delay. The rules depend on the size of the employer and how the coverage works. Before deciding to delay Part B:

1. Contact your employer's HR or benefits office and ask specifically whether your coverage is "primary" or "secondary" to Medicare
2. If your employer has fewer than 20 employees, Medicare typically becomes your primary coverage at 65 — delaying Part B in this situation can create gaps
3. Talk to a SHIP counselor (free, unbiased — find one at shiphelp.org) before making this decision

When your employer coverage ends, you will have a Special Enrollment Period (SEP) — typically eight months — to sign up for Part B without penalty.

The Late Enrollment Penalty

If you miss your Initial Enrollment Period and do not have a qualifying reason to delay, you will face a late enrollment penalty:

• Part B: Your premium increases by a percentage for each full 12-month period you were eligible but not enrolled. This penalty is permanent — it stays with you as long as you have Part B.
• Part D (prescription drugs): A similar penalty applies if you go without creditable drug coverage for 63 or more consecutive days after you first become eligible.

These penalties add up over time and are one of the most common and avoidable Medicare mistakes.

General Enrollment Period

If you missed your Initial Enrollment Period and do not qualify for a Special Enrollment Period, you can sign up during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins July 1 of that year. The late enrollment penalty still applies.

Annual Open Enrollment — Changing Your Coverage

Every year from October 15 through December 7, you can:

• Switch from Original Medicare to Medicare Advantage, or back
• Change from one Medicare Advantage plan to another
• Join, switch, or drop a Part D drug plan

Changes made during this window take effect January 1 of the following year. This is the time to review your plan and make sure it still fits your needs — especially your list of covered prescriptions and your preferred doctors.

How to Enroll

You can enroll in Medicare:

1. Online at ssa.gov (for Part A and Part B)
2. By calling Social Security at 1-800-772-1213
3. In person at your local Social Security office

For Medicare Advantage or Part D plans, you enroll through the private insurance company offering the plan, or through the plan finder at medicare.gov.