Medicare deadlines

The short answer

Your first chance to enroll is the Initial Enrollment Period around your 65th birthday. If you miss it and do not qualify for a Special Enrollment Period, the General Enrollment Period is the next yearly window. If you have active employer coverage, the eight-month Special Enrollment Period can let you delay Part B. The annual window is for changing Part D or Medicare Advantage coverage, not for your first Part B enrollment.

Initial Enrollment Period

The Initial Enrollment Period is a seven-month window. It starts three months before the month you turn 65 and ends three months after that month. If your birthday is on the first day of the month, the first-of-month rule can shift the window; use the official Medicare page to confirm your own dates.

The window is not a single deadline. The month you enroll can change when coverage starts. Enrolling before your birthday month can give you a coverage start earlier than your birthday month, while enrolling after it can leave a gap.

Read the Initial Enrollment Period guide for the month-by-month rules, or use the Medicare vs ACA tool if you are still working.

General Enrollment Period

The General Enrollment Period runs from January 1 through March 31 each year. It is for people who missed their first chance to enroll and do not qualify for a Special Enrollment Period. Coverage generally starts the month after you enroll, so a March application can still leave a gap for March.

A Part B late-enrollment penalty can apply for the months you went without Part B. The penalty is generally permanent. The Part B penalty calculator shows the monthly and long-term cost.

Special Enrollment Period while working

If you or your spouse have active employer coverage from an employer with 20 or more employees, you can usually delay Part B without a penalty. The Special Enrollment Period is generally eight months after the active coverage or employment ends. Retiree coverage and COBRA generally do not create the same window.

Keep the employer's written confirmation that the coverage is creditable and the exact start and end dates. The working past 65 guide explains the 20-employee rule and the proof to keep.

Annual enrollment window

The annual Medicare window runs from October 15 through December 7. It is the time to change Part D or Medicare Advantage coverage for the next plan year. It is not the window for your first Part B enrollment, and it does not replace the Initial Enrollment Period or a Special Enrollment Period.

Before the window, compare the plan's premium, deductible, formulary, and pharmacy network. The Part D out-of-pocket cap guide explains what the annual cap does and does not cover.

HSA stop date before Medicare

If you contribute to a Health Savings Account, stop contributions six months before Medicare Part A begins. Part A can be backdated up to six months, so the effective date can be earlier than the date you apply. A contribution made after the effective date can become an excess contribution.

The HSA and Medicare six-month rule guide explains the backdate and the correction steps.

ACA Marketplace open enrollment

The federal Marketplace open enrollment window is November 1, 2026 through January 15, 2027. State marketplaces can use different dates. A special enrollment period may apply after a qualifying life event, such as losing other coverage, moving, or a change in household size.

The ACA open enrollment guide explains the federal dates and the state exceptions. The employer affordability tool checks whether a job-based offer affects Marketplace help.

How to build your own timeline

1. Write down the month you turn 65 and the start and end of your seven-month window.
2. Mark whether you have active employer coverage and whether the employer has 20 or more employees.
3. If you are still working, write down the date the coverage or employment will end and add eight months.
4. If you contribute to an HSA, write down the date six months before Part A will start.
5. Put the annual October 15 to December 7 window on the calendar for plan changes.
6. Confirm every date with Social Security or the official Medicare page before you rely on it.

The Part B penalty tool can show what a missed window costs. The IRMAA tool covers a different deadline: the two-year income lookback.