Free Tool · Medicare & Colorado

Medicare Open Enrollment Checker

Updated October 2026

Medicare does not run on one calendar, it runs on several, and they do not overlap the way people assume. Pick the wrong window and you either miss your chance for the year or make a change you did not mean to make. Answer a couple of questions below and this tool will tell you which period applies to you right now, the real dates, and what to look at before you decide anything.

What this is, and is not: this tool is free and for information only. It is not run by Medicare, the Centers for Medicare & Medicaid Services, or Social Security, and it does not recommend or sell any plan. Nothing here is insurance advice. For free, unbiased help from a real person, call Colorado SHIP at 1-888-696-7213 (Spanish: 303-894-5953) or Medicare directly at 1-800-MEDICARE (1-800-633-4227), or visit medicare.gov.

Where are you starting from?

Start over

Before you choose a plan, check these

The drug list (formulary). Plans change which drugs they cover and what tier they're on every year. A drug that was cheap last year can jump tiers.
The pharmacy network. Your regular pharmacy can lose "preferred" status or drop out of network entirely for next year.
The doctor and hospital network, if you're looking at a Medicare Advantage plan. Original Medicare does not have this problem.
The plan's Annual Notice of Change (ANOC) letter. Plans mail this every September. It spells out exactly what's changing in your current plan for next year, premium, drug list, network, all of it.
Total yearly cost, not just the premium. Add up the deductible, copays, and the out-of-pocket maximum, not just the monthly bill.

All the Medicare enrollment periods, in plain English

Initial Enrollment Period

This is your first chance to sign up. It's 7 months long: it starts 3 months before the month you turn 65, includes your birthday month, and runs 3 months after. For premium-free Part A, coverage starts the month you turn 65 (the month before, if your birthday falls on the first of the month). For Part B: if you sign up before your birthday month, coverage starts the month you turn 65. If you sign up during your birthday month or in the 3 months after, coverage starts the next month.

Still working at 65? You may be able to wait

If you (or your spouse) are still working and covered by a job-based group health plan, you can often delay signing up for Part B with no penalty. Once that job-based coverage ends, or you retire, whichever comes first, you get an 8-month Special Enrollment Period to sign up for Part A and/or Part B. You can also sign up anytime while the job-based coverage is still active. One catch: you only get the first 2 months of that 8-month window to add a Medicare Advantage or Part D drug plan without risking a late penalty, so don't wait the full 8 months if you also need drug coverage.

Annual Open Enrollment Period: October 15 to December 7

This is the big one. If you already have Medicare, Original or Advantage, you can use this window every year to switch Medicare Advantage plans, move between Original Medicare and Advantage, or join, switch, or drop a Part D drug plan. The plan has to get your request by December 7. Whatever you choose takes effect January 1 of the next year.

Medicare Advantage Open Enrollment Period: January 1 to March 31

This one is only for people who already have a Medicare Advantage plan. You get one change: switch to a different Medicare Advantage plan, or drop Advantage and go back to Original Medicare (you can pick up a Part D plan at the same time if you do). It takes effect the first of the month after the plan gets your request. If you have Original Medicare, this window doesn't apply to you, it can't be used to join Advantage for the first time or to switch Part D plans on its own.

Special Enrollment Periods

Certain life events open a window outside the usual dates. If you move to a new address, your chance to switch plans runs 2 full months after the move (or starts the month before if you tell your plan ahead of time). If you lose job-based or union coverage, you get 2 full months after the month it ends. If you lose Medicaid eligibility, you get 3 full months from the date you're no longer eligible, or from when you're notified, whichever applies. Timing and what you're allowed to change both depend on the exact situation, so if yours doesn't match one of these cleanly, call Colorado SHIP or 1-800-MEDICARE and ask.

Extra Help (Part D Low-Income Subsidy)

Extra Help helps pay your Part D premium, deductible, and copays if your income and resources are limited. You can apply anytime, there's no deadline tied to the Annual Open Enrollment window. Apply through Social Security at ssa.gov/medicare/extra-help or by calling SSA at 1-800-772-1213. If you already have full Medicaid, SSI, or help through a Medicare Savings Program, you likely already qualify automatically. If you have Medicaid or Extra Help, you also get a Special Enrollment Period to switch Part D plans once per calendar month, any month.

One real-world wrinkle worth knowing: if you travel part of the year, a Medicare Advantage HMO plan can limit routine care to its own service area, which matters if you split time between Colorado and somewhere warmer in the winter. I wrote more about that tradeoff in Become a Snowbird Without Being Rich.

Sources

Dominic Ferrara

I spent 30 years in enterprise IT. Now I write plain, honest guides to the tech, travel, and healthy-living choices that actually work after 50. More about Dominic →