Medicare Enrollment Periods

All five windows at a glance

Window	When	What you can do
Initial Enrollment Period (IEP)	7 months — the 3 months before your 65th-birthday month, that month, and the 3 months after	Enrol in A, B, C, D; buy Medigap
Annual Enrollment Period (AEP)	October 15 – December 7	Change Advantage or Part D plans; switch between Original and Advantage
Medicare Advantage Open Enrollment (OEP)	January 1 – March 31	If in an Advantage plan: one switch, or return to Original Medicare
General Enrollment Period (GEP)	January 1 – March 31	Enrol in Part A/B if you missed your IEP and have no SEP
Special Enrollment Period (SEP)	Triggered by an event	Varies by trigger

Official details are on Medicare.gov.

Your Initial Enrollment Period, month by month

Seven months, centred on your birthday month — but when you sign up inside it changes when coverage starts.

• The 3 months before your birthday month — coverage starts the first day of your birthday month. This is what you want.
• Your birthday month — coverage starts the following month.
• The 3 months after — coverage starts the month after you sign up.

If your birthday falls on the 1st, everything shifts a month earlier. Sign up in the first three months and you avoid any gap; see when coverage starts.

The Annual Enrollment Period

Between October 15 – December 7 every year, anyone with Medicare can join, switch, or drop a Medicare Advantage or Part D plan, or move between Original Medicare and Advantage. Changes take effect January 1.

This is not optional maintenance. Plans change their premiums, formularies, networks, and extra benefits every year, and you're auto-renewed into next year's version if you do nothing. Read the Annual Notice of Change that arrives each September and check three things: your doctor, your drugs, and the out-of-pocket maximum.

What AEP does not give you is a guaranteed right to buy Medigap — that's a separate and much stricter rule.

Medicare Advantage Open Enrollment

From January 1 – March 31, if you're already enrolled in a Medicare Advantage plan on January 1, you get one opportunity to switch to a different Advantage plan or drop back to Original Medicare with a standalone Part D plan.

It's a safety net for a January that isn't working out. It doesn't apply if you're on Original Medicare, and it doesn't come with a Medigap guarantee.

The General Enrollment Period — the expensive one

If you missed your IEP and don't qualify for a Special Enrollment Period, you sign up between January 1 – March 31 with coverage starting the month after enrolment. You'll also carry the late-enrollment penalty.

The Part B penalty is 10% of the standard premium for each full 12-month period you could have had Part B but didn't — and unlike most penalties, it never goes away. Two years late means 20% added to your $202.90 premium for life. Our Part B penalty estimator shows the actual figure.

Special Enrollment Periods

Life events open a window outside the normal calendar. The most common:

• Leaving employer coverage — 8 months after the employment or the group coverage ends, whichever comes first. This is the one that lets you delay Part B without penalty while still working.
• Moving out of your plan's service area, or to somewhere with new options.
• Your plan leaving your county or its Medicare contract ending.
• Gaining or losing Medicaid or Extra Help.
• Moving into, living in, or leaving an institution.

Dual-eligible and Extra Help members generally get additional chances to change plans during the year. See Medicare.gov on joining a plan.

The Medigap window nobody tells you about

Separate from all of the above, your Medigap Open Enrollment Period runs for the 6 months that begin the month you're 65 or older AND enrolled in Part B. During it you can buy any Medigap policy sold in New Mexico with guaranteed acceptance.

After it closes, carriers may use medical underwriting in most situations — they can charge more or decline you outright. It's the only Medicare window that never comes back, which is why the Advantage-versus-Medigap decision at 65 carries more weight than it first appears. See Medicare.gov's Medigap timing rules.

Which window applies to you

If you're turning 65, it's your IEP. If you're already on Medicare and it's autumn, it's AEP. If something changed in your life, check whether it opened an SEP before assuming you have to wait.

Our enrollment timeline tool will place you, or read how to actually enrol next.

Not sure which of these fits you? A free 15-minute call with a licensed local advisor sorts it out — no pressure, and no cost to you. We do not offer every plan available in your area. For a complete list of every plan in your county, use Medicare Plan Compare or call 1-800-MEDICARE.

What each window does not let you do

Knowing the limits prevents the most common planning error.

Window	What it will not do
Annual Enrollment	Guarantee you a Medigap policy without health questions
Advantage Open Enrollment	Let you switch if you're on Original Medicare; allow more than one change
General Enrollment	Waive the late-enrollment penalty
Special Enrollment	Apply for events that don't qualify — retiree coverage and COBRA ending do not count as active employment

The practical consequence: people who choose Medicare Advantage at 65 assuming they can move to Medigap at any later Annual Enrollment are often surprised. You can apply — but you can also be declined.

Setting your own reminders

Medicare will not chase you, and the deadlines that cost the most are the quietest ones. Three dates are worth putting in a calendar now.

• Three months before your 65th birthday month — the start of your Initial Enrollment Period and the point at which enrolling gives you a clean start date.
• Each September — when your Annual Notice of Change arrives, in time to act before Annual Enrollment opens.
• Two months before any known coverage change — retirement, a spouse's retirement, or a move out of your plan's area.

If you're planning to retire, work backwards from the last day of your employer coverage rather than from your birthday, because that's the date the Special Enrollment Period keys off.