Medicare isn’t a one-and-done sign-up. It’s a series of windows that open and close throughout your life, and knowing which one you’re in keeps you from missing a deadline or paying a penalty you never had to. Here’s the whole roadmap in order.
It starts at 65: your Initial Enrollment Period
Your first window is the Initial Enrollment Period (IEP), a seven-month stretch built around your 65th birthday:
- The 3 months before your birthday month
- Your birthday month itself
- The 3 months after
This is the cleanest, penalty-free time to sign up for Part A and Part B and to add a plan like Medicare Advantage, a Medigap policy, or a standalone Part D drug plan. Enrolling in the first three months means your coverage is ready the day you turn 65; wait until the back half and your start date can slip by a month or more.
Not sure exactly when your window opens? The Timeline Calculator maps your personal dates from your birthday, and the Eligibility Calculator confirms you’ve got the work credits for premium-free Part A.
The windows that come back every year
Once you’re on Medicare, a few windows reopen on a regular schedule. Here’s how they line up:
| Window | When | What you can do |
|---|---|---|
| AEP (Annual Enrollment Period) | Oct 15 – Dec 7 | Switch between Original Medicare and Medicare Advantage, change Part D plans, join or drop drug coverage. Changes start Jan 1. |
| Medicare Advantage Open Enrollment | Jan 1 – Mar 31 | If you’re already in a Medicare Advantage plan: switch to another MA plan, or drop it for Original Medicare + a Part D plan. |
| GEP (General Enrollment Period) | Jan 1 – Mar 31 | A catch-up window if you missed your IEP. Coverage starts the first of the month after you enroll. |
The one most people use is AEP — the fall window where you review your plan for the coming year. Premiums, drug formularies, and provider networks all change yearly, so even a plan you love is worth a once-over. This is also where the 2026 changes show up: a $2,000 yearly cap on Part D out-of-pocket drug costs (the old “donut hole” is gone), and the first round of Medicare’s drug price negotiations taking effect January 1, 2026, on common medications like Eliquis and Jardiance. What you actually pay still depends on your specific plan.
A quick note on the difference between the two January–March windows: the Medicare Advantage Open Enrollment Period is only for people already in an MA plan, while the GEP is a fallback for folks who missed signing up entirely. They share dates but do very different jobs.
Life events open a window too: SEPs
Outside the regular calendar, certain life changes trigger a Special Enrollment Period (SEP) — a chance to make changes when something shifts. Common triggers include:
- Losing active employer coverage. This gives you an 8-month SEP to enroll in Part B without penalty.
- Moving out of your current plan’s service area.
- Qualifying for Extra Help or other assistance programs.
One important catch: only active coverage from an employer with 20 or more employees lets you delay Part B penalty-free. COBRA, retiree plans, and VA benefits do not count for this — so if you’re leaning on one of those, treat your IEP as your real deadline.
The mistakes that cost money
Most Medicare penalties come from missing a window, not from making a wrong choice inside one:
- Skipping Part B with no qualifying coverage. The late penalty adds 10% to your premium for each full 12 months you could have had it but didn’t, and it lasts as long as you have Part B.
- Going without creditable drug coverage. The Part D penalty is 1% of the national base premium ($38.99 in 2026) for each full month you went without — added to your premium permanently.
- Not reviewing during AEP. Plans change every year; staying on autopilot can quietly raise your costs.
If a deadline is sneaking up, the Enrollment Countdown shows exactly how many days you have left so nothing slips past you.
Putting the roadmap together
Here’s the timeline at a glance: sign up during your IEP at 65, then mark your calendar for AEP every fall (Oct 15 – Dec 7) to review your coverage. Keep the Jan 1 – Mar 31 windows in your back pocket for switching Medicare Advantage plans or catching up if you missed enrolling, and remember that life events can open an SEP anytime in between.
If you’re staring at these dates and not sure which one applies to you — or you just want a second set of eyes before a deadline — that’s exactly what I’m here for. Feel free to reach out for a no-pressure call, and we’ll make sure your timeline lines up the way it should.