How to Change Your Part D Plan: Dates, Steps and Exceptions

You can change your Medicare Part D plan during the Open Enrollment Period, which runs October 15 through December 7 every year. A change made in that window starts January 1. Outside it, you generally need a Special Enrollment Period. The work is in choosing the right replacement plan: one that covers your actual prescriptions at your pharmacy for the lowest total yearly cost. At Simply Insurance, we help Colorado residents compare Part D plans across multiple carriers, at no direct cost to the client, and we stay with you after you enroll.

SimplyinsuranceforyouCompare Part D Plans With GuidanceSimply Insurance helps Colorado residents compare Part D plans across multiple carriers and provides ongoing support after enrollment.Visit

TL;DR

• The main window to switch is October 15 to December 7 each year, and the new plan starts January 1.
• You don’t cancel your old plan. Joining the new plan ends the old drug coverage when the new one begins.
• Outside the fall window, a Special Enrollment Period (a move, a loss of employer coverage, Medicaid or Extra Help) can allow a change.
• Going 63 or more days without creditable drug coverage can lead to a lifelong late enrollment penalty, so never leave a gap.
• Compare using your exact drug list, pharmacy and dosage. Premium alone is a poor guide.

Table of Contents

• When you can change a Part D plan
• Why reviewing your plan every year matters
• How to change your Part D plan, step by step
• What happens to your coverage during the switch
• Changing outside the fall window
• Avoid the late enrollment penalty
• Mistakes to avoid when switching
• Where we can help
• Our view: the plan you picked last year is not the plan to keep by default
• FAQ
• Sources

When you can change a Part D plan

There is one dependable window and a handful of exceptions.

The Open Enrollment Period (October 15 to December 7). Medicare.gov says that a plan change made by December 7 takes effect January 1 of the following year. Colorado’s Division of Insurance gives the same dates for people in the state: you can enroll in or switch Part D plans from October 15 to December 7, with the selection effective January 1. During this period you can change your choice as often as you like. Only your last choice, received by the deadline, counts.

Your Initial Enrollment Period. When you first become eligible for Medicare, you choose your first drug plan. If you are turning 65, our Medicare enrollment timeline shows how the windows line up.

The Medicare Advantage Open Enrollment Period (January 1 to March 31). This is for people already in a Medicare Advantage plan. According to CMS, it does not give someone in Original Medicare a general mid-year chance to switch stand-alone Part D plans. If you have a stand-alone drug plan with Original Medicare, you generally wait for fall unless a Special Enrollment Period applies.

A Special Enrollment Period. These are tied to specific life events, covered below.

The calendar repeats every year, so if you are reading this in the fall, the window is probably open now. Check the official Medicare site for the current year’s exact deadline before you act.

Why reviewing your plan every year matters

You don’t have to do anything to stay in your current plan. But Colorado’s insurance regulator advises that continuing members should still review yearly changes, because premiums, copayments and covered-drug lists can change from one year to the next.

There is a catch in the paperwork. The same state guidance notes that the Annual Notice of Change covers premiums and general changes, but does not have to list changes to covered drugs. A plan can look the same on paper while your medication moves to a higher tier or loses coverage. That is why a drug-by-drug check each fall is worth the time.

The benefit itself has also changed. Part D has a redesigned structure, and our guide to Medicare prescription drug costs explains the new yearly cap. We also cover the $2,100 out-of-pocket cap and how it affects what you pay. For the broader picture, see our overview of Medicare changes for 2026.

How to change your Part D plan, step by step

Step 1: Write down every medication

List each prescription with its dose, how often you take it and the pharmacy you use. Include generics, brand-name drugs and anything you take occasionally. A missing drug is the most common reason a plan that looked cheap turns out expensive.

If one of your prescriptions is a newer or specialty therapy, such as those in a peptide therapy cost breakdown, list it by name and confirm with each plan how it is handled before you commit.

Step 2: Compare plans on total yearly cost

Medicare.gov’s Plan Compare tool lets you enter your drugs and see coverage, pharmacies, premiums, deductibles and estimated yearly drug costs side by side. Look at four things:

1. Formulary: is each drug on the plan’s list, and at which tier?
2. Pharmacy network: is your pharmacy preferred, standard or out of network?
3. Premium plus deductible: a low premium can come with a deductible that raises your early-year costs.
4. Estimated annual total: this combines everything and is the number to compare.

This is where an independent broker earns the time. We work across multiple carriers and match the plan to your drug list, rather than starting from one company’s lineup. Our Medicare Part D plans in Castle Pines page explains what we offer, and there is no direct cost to you for our help.

Step 3: Enroll in the new plan

You can enroll through Medicare.gov, contact the plan directly, or call 1-800-MEDICARE. The Medicare number is 1-800-633-4227, and TTY users can call 1-877-486-2048. If you enroll with us, we complete the application as part of the enrollment support we provide.

Step 4: Leave the old plan alone

This surprises people. Medicare.gov explains that you generally change plans simply by joining the new one. The old drug coverage ends when the new coverage begins, so you should not cancel it separately. Cancelling first can leave you with no drug coverage at all.

Step 5: Confirm and keep your paperwork

After you enroll, watch for the plan’s welcome materials and your new member ID card, and confirm the pharmacy you use accepts the plan before January. Keep the confirmation of your enrollment. If you made several changes in the window, check that the last one is the plan you want.

What happens to your coverage during the switch

Situation What happens You switch during October 15 to December 7 New plan starts January 1; old plan ends then You do nothing Your current plan continues, with whatever changes it made for the new year You cancel the old plan with no replacement You may have no drug coverage and risk a penalty You switch to Medicare Advantage You may be able to drop stand-alone Part D, as most Advantage plans include drug coverage

The last row matters if you are weighing a bigger change. Moving from Original Medicare to Medicare Advantage replaces the structure of your coverage, not only the drug plan. Our comparison of Medicare Advantage vs. Medigap lays out the trade-offs, and our Medicare Advantage plans page covers Colorado options.

Changing outside the fall window

A Special Enrollment Period lets you switch when something in your life changes. CMS lists qualifying circumstances that can include moving, losing or changing employer or union coverage, gaining Medicaid or Extra Help, entering or leaving an institution, joining PACE, plan termination, or certain exceptional situations.

Moving. CMS guidance says a permanent move outside your plan’s service area, or to an area with different plan options, can create a Special Enrollment Period. It generally begins around the time of the move or when you notify the plan. If you are relocating within Colorado or arriving from another state, check whether your current plan is still available at the new address.

Medicaid or Extra Help. Since 2025, people with Medicaid or Extra Help may have monthly Special Enrollment Period rights, according to the National Council on Aging, letting eligible people in Original Medicare switch stand-alone Part D plans, with the new plan generally starting the first day of the following month.

Losing other coverage. If you lose employer or union drug coverage, you may qualify for a window to join a Part D plan. Our guide to Medicare special enrollment for workers covers the timing rules.

The details of each Special Enrollment Period, including how long it lasts, vary by situation. If you think you qualify, we can confirm it before you try to enroll, so you don’t submit a request that gets denied.

Avoid the late enrollment penalty

The most expensive mistake in a plan change is a gap in coverage. CMS says that if you go 63 or more consecutive days after your Initial Enrollment Period without Part D or other creditable drug coverage, you may owe a late enrollment penalty when you later enroll. The penalty generally continues for as long as you have Medicare drug coverage. People who qualify for Extra Help do not pay it.

Two habits keep you safe:

• Switch by joining, never by dropping. See Step 4 above.
• Check whether your other coverage is creditable. Medicare’s drug coverage publication says examples include employer or union coverage, and that you should ask your current provider whether coverage is creditable before dropping or changing it.

If you want to see what a gap could cost, our Part D penalty calculator gives an estimate. To understand the benefit more broadly, read what Medicare Part D covers in 2026.

Mistakes to avoid when switching

Choosing by premium alone. A $0 premium plan can cost more overall if your drugs sit on a high tier or if the deductible is large. Compare the estimated annual total.

Skipping the pharmacy check. The same plan can price your prescription differently depending on the pharmacy. Confirm yours is in the network and whether it is preferred.

Relying on last year’s notice. As noted above, the Annual Notice of Change does not have to list drug changes. Check the formulary directly.

Waiting until the last day. Colorado’s regulator reminds beneficiaries they can compare next year’s plans on Medicare.gov during Open Enrollment. Give yourself time to fix a problem before the window closes.

Forgetting a medication change. If your doctor adds or changes a drug during the year, review your plan again in the fall rather than assuming last year’s choice still fits.

Where we can help

Changing a plan is simple in principle and fiddly in practice: drug lists, tiers, pharmacy networks and deadlines all interact. Simply Insurance is an independent brokerage serving Castle Pines and Colorado. Our licensed brokers compare Part D plans across multiple carriers, and our Annual Enrollment (AEP) service is built for exactly this fall review. There is no direct cost to you for our help. We also help after enrollment, including with appeals and grievances if a plan denies a drug.

Start with our Medicare Part D plans page, or see everything we offer on our services page.

Our view: the plan you picked last year is not the plan to keep by default

We meet people every fall who stayed in a plan for years because it was easy. Part D is the part of Medicare that changes the most from year to year, so a quiet renewal is a decision too, only a less informed one.

Our approach is to start from your prescription list, not from a carrier’s brochure. Because we are independent and work across multiple carriers, we can compare plans on what you would actually pay, and we revisit that every year in an annual review rather than only when you first enroll.

We also think support should not end at enrollment. If a drug is denied, or a claim is not handled the way you expected, we are there for appeals and grievances. That ongoing relationship is what we believe makes Medicare simpler for our clients in Castle Pines and across Colorado.

Zach

FAQ

When can I change my Part D plan?

The main window is October 15 to December 7 each year, with the new plan starting January 1. You may also switch with a Special Enrollment Period after a qualifying event, such as a permanent move or gaining Medicaid or Extra Help. People in Medicare Advantage have an additional window from January 1 to March 31.

Do I need to cancel my old Part D plan first?

No. You generally change plans by joining the new one, and the old coverage ends when the new coverage begins. Cancelling on its own can leave you without drug coverage and may lead to a late enrollment penalty.

Can I switch Part D plans in the middle of the year?

Only if you qualify for a Special Enrollment Period. Common reasons include moving out of your plan’s service area, losing employer or union coverage, or qualifying for Medicaid or Extra Help. Without one of these, you generally wait for the fall Open Enrollment Period.

How do I know which Part D plan is cheapest for me?

Compare estimated yearly total cost, not premium alone, using your exact drugs, doses and pharmacy. Medicare.gov’s Plan Compare tool does this, and our brokers can run the comparison across multiple carriers for you at no direct cost.

What happens if I miss the deadline?

Your current plan generally continues into the next year, with any changes the plan made. You would then wait until the next Open Enrollment Period unless a Special Enrollment Period applies. If you think one applies, contact us and we will help you check.

Sources

• Joining a plan | Medicare
• What if I want to switch, drop, or rejoin drug coverage? | Medicare
• Understanding Medicare Advantage and Medicare drug plan enrollment periods | CMS
• PDP Enrollment and Disenrollment Guidance | CMS
• Part D Special Enrollment Periods 2026 | National Council on Aging
• Colorado Medicare Health/Drug Insurance Coverage Options | Colorado Division of Insurance
• Consumer Advisory: Medicare Open Enrollment | Colorado Division of Insurance
• Choosing Medicare drug coverage | Medicare

Recommended

• What Is Medicare Part D in 2026? Formularies, Premiums, and
• Medicare Changes 2026: Costs, Part D and Advantage Updates
• Medicare Part D Penalty Calculator
• Medicare Prescription Drug Costs 2026: New Cap