Signing up for Medicare at the wrong time can trigger penalties that follow you for the rest of your life. That’s not an exaggeration. Miss your Initial Enrollment Period by even a couple of months, and you could pay 10% more on your Part B premium permanently. Miss Part D enrollment, and that penalty stacks on top of your drug plan premium every month, for as long as you have Medicare.
The enrollment rules aren’t complicated once you see them laid out clearly. Let’s walk through each enrollment window so you know exactly when to act.
Your Initial Enrollment Period: The 7-Month Window
This is the most critical enrollment period, and it’s the one that trips up the most people. Your Initial Enrollment Period (IEP) starts three months before the month you turn 65, includes your birthday month, and extends three months after. That’s a seven-month window total.
For example, if your 65th birthday is in September 2026, your IEP runs from June 2026 through December 2026. Sign up during the three months before your birthday if you want coverage to begin as close to your birthday month as possible. Waiting until after your birthday month means a delay before coverage kicks in.
During your IEP, you can enroll in Medicare Part A, Part B, a Medicare Advantage plan, and a Part D prescription drug plan. This is also your guaranteed-issue window for Medigap, meaning no insurance company can turn you down or charge you more for a Medicare Supplement plan based on your health.
What if You’re Still Working at 65?
If you have employer-sponsored health insurance through your job (or your spouse’s job) at a company with 20 or more employees, you can delay Medicare enrollment without penalty. You’ll get a Special Enrollment Period (SEP) that gives you eight months to sign up after you lose that employer coverage or stop working, whichever comes first.
This is where a lot of people get tripped up. If your employer has fewer than 20 employees, Medicare becomes your primary insurer at 65 regardless. Delaying enrollment in that situation triggers the late penalty. If you’re unsure about your employer’s size or how it affects your Medicare timing, talk to your HR department and a licensed agent before your 65th birthday.
Annual Open Enrollment: October 15 Through December 7
This is the big one that gets all the TV commercials. The Annual Enrollment Period (AEP) runs from October 15 through December 7 every year. Changes you make during this window take effect on January 1 of the following year.
During AEP, you can switch from Original Medicare to a Medicare Advantage plan (or the other way around), change from one Advantage plan to another, join or switch a Part D drug plan, or drop drug coverage. This is the time to review your plan’s Annual Notice of Change document, which your current plan is required to send you by September 30 each year.
Plans change their networks, formularies, and costs annually. Just because your plan worked well last year doesn’t mean it’s still the best fit. A 10-minute review every fall can save you hundreds of dollars over the course of a year.
Medicare Advantage Open Enrollment: January 1 Through March 31
If you’re already enrolled in a Medicare Advantage plan and you’re unhappy with it, this window gives you a second chance. From January 1 through March 31, you can switch to a different Medicare Advantage plan, or drop your Advantage plan and go back to Original Medicare (and add a Part D plan if needed).
You can only make one change during this period, unlike the fall AEP where you can change your mind multiple times. And this window only applies to people already in a Medicare Advantage plan.
Late Enrollment Penalties: What They Actually Cost
The Part B late enrollment penalty is 10% of the standard premium for each full 12-month period you could have had Part B but didn’t. The 2026 standard Part B premium is $202.90. If you delayed two years without qualifying for an exemption, you’d pay roughly $40 extra per month on top of that premium, every month, for the rest of your life.
Part D penalties work similarly. The late enrollment penalty is 1% of the national base beneficiary premium multiplied by the number of months you went without creditable drug coverage. It adds up fast and never goes away.
Get Help Before Your Deadline Passes
Medicare enrollment timelines are strict, and the penalties for missing them are real. Whether you’re approaching 65, leaving employer coverage, or just want to make sure your current plan is still the right one, Fabian Ramirez Insurance Agency is here to help. Fabian has been guiding Medicare beneficiaries in Victoria and the Texas Crossroads for more than 18 years. Call (361) 652-3005 to schedule a free enrollment review.
