Medicare 2026

Medicare enrollment windows that shape your path in Billings

BILLINGS, Mont. — For people here weighing Original Medicare with a Medigap policy against a Medicare Advantage plan, the biggest factor isn't always the coverage itself. It's the calendar. The path you take — and how easily you can switch later — is shaped by a handful of enrollment windows, and missing one can lock in a choice for a long time.

Two paths, two different rulebooks

Original Medicare is the federal program — Part A (hospital) and Part B (medical). Many people pair it with a stand-alone Part D drug plan and a Medigap policy, which is private insurance that helps pay costs Original Medicare leaves behind.

Medicare Advantage (Part C) is different. It's a private plan that replaces the way you get your Part A and Part B benefits, usually bundles in drug coverage, and often uses a network. Billings sits in Yellowstone County, where multiple Medicare Advantage plans are offered — but the number of options isn't what should drive your timing decisions.

The two paths share some enrollment windows and have some that are unique. That's where people get tripped up.

Your first window: the Initial Enrollment Period

Most people first become eligible for Medicare around their 65th birthday. Your Initial Enrollment Period is a seven-month window: the three months before your birthday month, your birthday month, and the three months after.

During that window you can sign up for Part A and Part B, join a Part D drug plan, or choose a Medicare Advantage plan. Miss it without other qualifying coverage, and you can face lifelong late-enrollment penalties for Part B and Part D.

The Medigap window most people don't realize is one-and-done

Here is the deadline that quietly matters most for the Original Medicare + Medigap path: your Medigap Open Enrollment Period.

It's a six-month window that starts the month you're 65 or older and enrolled in Part B. During those six months, Medigap insurers in Montana must sell you any policy they offer at their standard rate, regardless of health history.

After that window closes, in most situations, insurers can use medical underwriting — meaning they can ask health questions and decide whether to sell you a policy and at what price. A few limited "guaranteed issue" rights exist later (for example, if certain coverage ends involuntarily), but they're the exception.

That's why the choice between the two paths isn't purely a today decision. Choosing Medicare Advantage at 65 is easy to do; switching back to Original Medicare with a Medigap policy years later may not be, depending on your health and state rules.

The fall window: Annual Enrollment, Oct. 15 – Dec. 7

Every fall, from Oct. 15 through Dec. 7, anyone with Medicare can:

• Switch from Original Medicare to a Medicare Advantage plan, or vice versa.
• Change from one Medicare Advantage plan to another.
• Join, drop, or change a Part D drug plan.

Changes made in this window take effect Jan. 1, 2027. This is the main time to review your drug coverage, since Part D plans change each year. The Part D out-of-pocket cap is $2,100 in 2026 and $2,400 in 2027, and the maximum deductible is $615 in 2026 and $700 in 2027. The old "donut hole" coverage gap is gone — replaced by a three-phase structure. An optional Medicare Prescription Payment Plan lets you spread drug costs across the year in monthly amounts.

Note: Annual Enrollment does not give you a new right to buy a Medigap policy without underwriting. That's a common and costly assumption.

The spring window: Jan. 1 – March 31

The Medicare Advantage Open Enrollment Period runs Jan. 1 through March 31. It applies only to people already enrolled in a Medicare Advantage plan. During it, you can:

• Switch to a different Medicare Advantage plan, or
• Drop your Medicare Advantage plan and go back to Original Medicare (and add a Part D plan).

Again, going back to Original Medicare doesn't automatically come with a guaranteed right to buy a Medigap policy. Check with a licensed source before making the move.

Special Enrollment Periods

Life events — moving out of a plan's service area, losing employer coverage, qualifying for Extra Help, moving into or out of a nursing facility — can open a Special Enrollment Period. These are the safety valves when a fixed window doesn't fit real life. If something changes for you mid-year, call 1-800-MEDICARE before assuming you have to wait until fall.

One more date worth knowing: IRMAA, the income-related surcharge on Part B and Part D premiums, starts above $109,000 for a single filer in 2026. It's tied to your tax return from two years earlier, so a big income year can affect premiums later.