By Marc Gilman
Questions? Call (800) 927-9326 or email
Plenty of people end up with Part A but not Part B — often because they were still working and covered by an employer plan when they turned 65, and Part A was free so they took it and left Part B alone. That’s usually the right call at the time. But eventually the employer coverage ends, or you decide you’re ready to add Part B, and the question becomes: how do you actually sign up now?
The answer depends entirely on why you don’t have Part B yet.
Key Takeaways
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How you enroll depends on whether you’re still covered by an employer plan or missed your original window entirely.
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If you have current employer group coverage, you likely qualify for a Special Enrollment Period (SEP) — no waiting, no penalty.
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If you don’t have employer coverage, you’ll need the General Enrollment Period, which runs January 1 to March 31 each year, with coverage starting the month after you sign up.
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Missing your original window without qualifying coverage can trigger a late enrollment penalty that lasts for as long as you have Part B.
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Applications can be completed online at ssa.gov, or by fax/mail using forms CMS-40B and, if applicable, CMS-L564.
Do You Qualify for a Special Enrollment Period?
If you’re still working past 65 and covered by a group health plan through your own or a spouse’s current employer, you’re not on the clock. You can add Part B at any time while that coverage continues, or within 8 months after it ends or you stop working — whichever comes first. This is the Special Enrollment Period, and it comes with two advantages: you can apply any time of year, and there’s no late enrollment penalty for the time you spent on employer coverage instead.
To use the SEP, you’ll need to show Social Security that the coverage was real and current. Acceptable proof includes a completed CMS-L564 (your employer fills out part of it), pay stubs showing premium deductions, W-2s reflecting pre-tax medical contributions, or a health insurance card with an effective date.
One timing detail worth getting right: in the Remarks section of your application, state the month and year you want Part B to start, and try to line it up with the first of the month right after your employer coverage ends. Landing that date correctly is what prevents a coverage gap.
What If You Don’t Have Employer Coverage?
If your employer coverage already ended more than 8 months ago — or you never had it — the SEP door has closed, and you’ll need the General Enrollment Period (GEP) instead. The GEP runs January 1 through March 31 every year, and coverage now begins the first day of the month after you enroll (Medicare eliminated the old rule that pushed everyone’s start date to July 1, so there’s no longer a long wait built into this window).
The trade-off with the GEP is that you’re limited to once a year, and if you went a full 12-month period or more without Part B or other qualifying coverage after you were first eligible, a late enrollment penalty likely applies.
How Do You Actually Apply?
However you got here, applying is the same either way:
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Online — the fastest option. Go to ssa.gov/medicare/sign-up, and if you already have Part A and just need Part B, look for the “Sign up for Part B only” path. You’ll sign the application electronically, so have an email address ready.
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By fax or mail — complete CMS-40B (Application for Enrollment in Medicare – Part B), and if you’re applying under an SEP, also complete CMS-L564 (Request for Employment Information). Send both to your local Social Security office.
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By phone — call Social Security at 1-800-772-1213 (TTY 1-800-325-0778), Monday through Friday, 8 a.m. to 7 p.m.
Read the form instructions closely before submitting. Incomplete or mismatched documentation — for example, employer dates on CMS-L564 that don’t match what you stated elsewhere — is the most common reason applications get delayed or kicked back.
What Happens After You Apply?
Once Social Security processes your application, you’ll receive an updated Medicare card showing both Part A and Part B. The Part B premium — $202.90 per month for most people in 2026, more if your income is above certain thresholds — is deducted automatically from your Social Security benefit if you’re already collecting one. If you’re not yet collecting Social Security, you’ll be billed directly for Part B instead.
Will You Pay a Late Enrollment Penalty?
This is the part worth taking seriously. If you didn’t have Part B or other creditable coverage (like current employer coverage) during your Initial Enrollment Period, and you’re now signing up through the General Enrollment Period, Medicare adds 10% to your Part B premium for every full 12-month period you went without it. That penalty isn’t a one-time fee — it’s added to your premium for as long as you have Part B, which for most people is the rest of their life.
If you had qualifying employer coverage the whole time and are using the SEP, none of this applies to you. The penalty is specifically about gaps that weren’t covered by something equivalent.
What To Do Next
If you’re not sure which path applies to you — SEP or GEP — or you want a second set of eyes on your documentation before you submit, that’s exactly the kind of thing we help people sort through every week. A wrong date in the Remarks section or a missing document is a small mistake that can cost months of delay.
If you’re comparing what a Medicare Supplement or Advantage plan would look like once Part B is active, reach out and we’ll walk through your options before you enroll.
Questions? Call (800) 927-9326 or email
