Medicare 2026

Medicare Late Penalties: The Dates That Decide Your Costs

SAN ANTONIO — Missing a Medicare enrollment window can cost you every month for the rest of your life. That's not a scare tactic — it's how the program is built. The good news for readers here in San Antonio is that the penalties for Part B and Part D are almost entirely avoidable if you know which dates apply to you and act inside them.

This guide walks through the timing: which windows open when, what happens if one closes on you, and how the deadlines fit together.

The first window: your Initial Enrollment Period

For most people, the clock starts at 65. Your Initial Enrollment Period (IEP) runs seven months: the three months before the month you turn 65, your birthday month, and the three months after.

If you're already getting Social Security, you'll be enrolled in Part A and Part B automatically. If you're not, you have to sign up yourself at ssa.gov or by calling Social Security. Part D is always something you choose and enroll in separately.

Miss the IEP without other creditable coverage, and the penalty math starts running in the background — even if you don't feel it until you finally sign up.

What happens if you miss it: the General Enrollment Period

If you didn't enroll during your IEP and don't qualify for a Special Enrollment Period, you can sign up for Part B during the General Enrollment Period, which runs January 1 through March 31 each year. Coverage begins the month after you enroll.

That's also typically when the Part B late penalty gets calculated and added to your premium. The formula: 10% of the standard Part B premium for every full 12-month period you could have had Part B but didn't. In most cases, that surcharge stays on your bill for as long as you have Part B.

The Part D deadline works differently — and it's easy to miss

Part D has its own timing. You generally need to enroll in a Part D plan (or a Medicare Advantage plan that includes drug coverage) when you're first eligible, unless you have creditable drug coverage from another source, such as an employer or union plan.

Go 63 days or more without creditable drug coverage after your Initial Enrollment Period ends, and a penalty starts building. The formula: 1% of the "national base beneficiary premium" for each full month you went without it. That amount gets added to your Part D premium every month, generally for life.

The trap: people often assume that because they don't take medications now, they can skip Part D and sign up later. The penalty keeps growing in the meantime.

Special Enrollment Periods: the safety valve for workers

If you're still working past 65 and covered by an employer group health plan (yours or your spouse's), you don't have to enroll in Part B or Part D right away. When that job coverage ends, you get:

• Part B: an 8-month Special Enrollment Period starting the month after employment or the group coverage ends — whichever comes first.
• Part D: a 63-day window after your creditable drug coverage ends to join a Part D or Medicare Advantage drug plan.

Note that COBRA and retiree coverage do not count as active employer coverage for the Part B SEP. If you're on COBRA, the 8-month Part B clock started when your job coverage ended, not when COBRA ends. This is one of the most common — and most expensive — misunderstandings.

How the windows fit together each year

Once you're enrolled, two annual windows matter:

• Annual Enrollment Period (Oct. 15 – Dec. 7): anyone with Medicare can join, switch, or drop a Part D plan or a Medicare Advantage plan. Changes take effect Jan. 1.
• Medicare Advantage Open Enrollment Period (Jan. 1 – March 31): if you're already in a Medicare Advantage plan, you get one chance to switch to another MA plan or return to Original Medicare.

Neither of these fixes a missed initial deadline for Part B — that's what the General Enrollment Period is for. But they're your regular chance to review Part D coverage so a plan change doesn't accidentally leave you without creditable drug coverage.

The 2027 backdrop

A few program-level numbers worth knowing as you weigh coverage in 2026: Part D now has an annual out-of-pocket cap of $2,100, the maximum Part D deductible is $615, and the old "donut hole" coverage gap has been eliminated. Higher earners — generally above $109,000 in income for a single filer — pay IRMAA surcharges on top of standard premiums. There's also an optional Medicare Prescription Payment Plan that lets you spread drug costs across the calendar year instead of paying big bills at the pharmacy counter.

San Antonio is in Bexar County, where a wide range of stand-alone Part D and Medicare Advantage plans are offered each year, so most residents have options to compare during the fall enrollment window.