Plain-English guide
Which Medicare window is yours?
Medicare doesn't have one sign-up date — it has several, each for a different purpose. Using the right one keeps you penalty-free and in the plan you meant to pick. Here's the whole map.
Initial Enrollment Period (IEP)
The 7 months around your 65th birthday — the 3 months before, your birthday month, and the 3 months after.
When you first become eligible. Sign up here to avoid late penalties, unless you have active coverage from a current job.
General Enrollment Period (GEP)
January 1 – March 31 each year.
A fallback if you missed your IEP and don't have creditable coverage. Coverage now starts the first of the month after you enroll — but a late penalty may apply.
Medicare Open Enrollment (AEP)
October 15 – December 7 each year.
Once you have Medicare: join, switch, or drop a Medicare Advantage or Part D drug plan. Changes take effect January 1.
Medicare Advantage Open Enrollment
January 1 – March 31 each year.
If you're already in a Medicare Advantage plan, switch to another MA plan or go back to Original Medicare (with a Part D plan).
Special Enrollment Periods (SEP)
Triggered by an event — e.g., an 8-month window after coverage from a current job ends.
For life changes: losing employer coverage, moving, or other qualifying situations. An SEP is how you avoid a penalty if you delayed because you had creditable coverage.
Free help first
Windows and exceptions get personal fast. Free, unbiased help is a call away:your local SHIP(1-877-839-2675) or Medicare.gov.
Common questions
I have coverage through my job at 65 — do I have to sign up now?
Often you can safely delay Part B (and Part D) while you have active coverage from your or a spouse's current employer, then use a Special Enrollment Period when it ends — without a penalty. Confirm your situation with your benefits administrator and SHIP; the rules differ for retiree coverage and for smaller employers. Source: Medicare.gov.
What's the difference between the fall Open Enrollment and the ACA marketplace's?
They're different systems. Medicare's Open Enrollment (Oct 15 – Dec 7) is for Medicare Advantage and Part D. The ACA Marketplace has its own separate open-enrollment window for people under 65. If you're on Medicare, the Medicare windows are the ones that apply to you. Source: Medicare.gov.
Source: Medicare.gov (enrollment periods, Special Enrollment Periods, creditable coverage). Dates and rules are federal and can change; confirm at Medicare.gov or with SHIP. We are not connected with or endorsed by the U.S. government. General information, not insurance advice. Last reviewed: 2026.