The short answer
You change drug plans by joining the new one during an enrollment window, not by cancelling the old one first. Medicare Open Enrollment runs October 15 to December 7 and new coverage starts January 1. You compare plans by entering the drugs you actually take.
Plan year 2026. No figure on this page changes with the plan year. The dates are statutory and the tier labels come from Medicare.gov's own worked example, so no year is attached to them inside a sentence.
You did not change your prescriptions. You did not change your plan. You went to the pharmacy in March and the price was different, because the plan changed its list and the letter telling you so had already arrived.
How do I change Medicare Part D plans?
You join a different Medicare-approved plan during an enrollment window. Medicare.gov gives three routes for doing it: select Enroll for the plan at Medicare.gov/plan-compare, contact the plan by phone or on its website, or call 1-800-MEDICARE at 1-800-633-4227.
A paper form is allowed too, and it carries a condition worth reading twice. You can ask the plan for a form to fill in and mail back, but the plan must have it before your enrollment period ends. The deadline belongs to their receipt of it, not to your posting of it.
Here is the pattern underneath all of that. Medicare.gov's own Part D page sends the question of changing plans to its enrollment period table, and so does its creditable coverage page. Two separate drug pages route the same question to the calendar.
Call it Changing A Drug Plan Is A Calendar Question. The routing is the government's and it is visible on both pages; naming the pattern is ours. It is a useful frame, because it tells you where the real constraint sits.
When can I change?
Medicare Open Enrollment, October 15 to December 7, lets anyone in Original Medicare join, drop or switch a Medicare drug plan. If you are in a Medicare Advantage plan, the January 1 to March 31 window lets you change your drug coverage as part of changing that plan.
Those windows have their own articles in this publication's enrollment cluster, and that is where the detail belongs. This page names them once and points, which is the same split Medicare.gov makes on its own site.
Special Enrollment Periods also exist for certain situations in your life, such as moving to a new address, losing or changing your current coverage, getting Medicaid, or getting Extra Help to pay drug costs.
Every one of those is something that happens to you. Which leaves the ordinary year, where nothing happens to you and the plan changes anyway.
Why should I review my plan every year?
Because the plan can change while you do nothing. A Medicare drug plan can change its drug list during the year under guidelines set by Medicare, when drug therapies change, when new drugs are released, or when new medical information becomes available. Plans can change that list at any time.
Your own cost can move without your drugs changing at all. Your coinsurance may rise for a drug when the manufacturer raises the price. It may also rise if you keep taking a brand name drug after your plan adds a generic version and moves the brand to a higher cost tier.
There is a protection attached, and it is worth knowing so you can watch for it. Your plan must notify you of any changes to its drug list that affect drugs you are taking.
Insurance companies also decide each year whether to join or leave Medicare, so the set of plans available to you is not fixed either.
None of that is a reason to switch. It is the reason to look.
How do I compare plans for my drugs?
Compare on your own prescriptions rather than on the premium. Medicare.gov's instruction is to find the plans available in your area and enter the drugs you take, which produces an estimate of your monthly and yearly cost under each plan.
Then check the things a price estimate does not show. Medicare names four checks, and the estimate performs only the first of them.
| What you check | What answers it | The trap |
|---|---|---|
| Your own prescriptions, entered | An estimate of your monthly and yearly cost | Comparing on the premium instead |
| Whether the plan covers your drugs | The plan's own list of covered drugs | An estimate is not proof of coverage |
| Whether your doctors and pharmacies are in network | Ask your doctors and your pharmacy | The estimate is silent on this |
| Whether it covers you in another state | Ask the plan | Only matters if you live there part of the year |
Three of those four are questions you have to ask somebody. Only the first is answered by the tool.
A plan's list of covered drugs is called a formulary, and each plan has its own. Every plan must cover a wide range of drugs and must include most drugs in certain protected classes: cancer drugs, HIV/AIDS drugs, antidepressants, antipsychotics, anticonvulsants, and immunosuppressants for organ transplants.
Within that list, plans sort drugs into tiers to lower costs, and a drug in a lower tier generally costs you less. Medicare.gov's tier example, and what sits in each tier, is set out in this publication's article on Part D drug tiers, which is where that ground belongs.
If your drug is not on a plan's list, a similar drug is usually available. If you or your prescriber believe none of them will work, you can ask for an exception, and your prescriber must supply a statement giving the medical reason.
That is how you pick the next plan. The question people ask second is what becomes of the one they are standing in.
What happens to my old plan?
Medicare.gov's pages read for this article do not describe what happens to a standalone drug plan you leave behind when you join a different one. That is stated plainly here rather than filled in, because a guess about coverage is the one thing this publication will not print.
What the government does state is narrower and worth knowing. A Medicare Advantage plan can disenroll you for several reasons, and one of them is joining a drug plan, in some cases. Moving outside the plan's service area, losing Medicare or Medicaid eligibility, and the plan's contract with Medicare ending are the others.
In those situations there is a grace period during which you are eligible for a Special Enrollment Period, and Medicare.gov's instruction is to review your options then so you keep the health and drug coverage you want.
There is one more piece of paperwork that can cost money for years. When you join a drug plan or health plan it may send you a letter asking whether you had creditable prescription drug coverage. If you do not return it by the deadline in the letter, the plan will not know you had that coverage, and you will be charged a late enrollment penalty.
For certainty about a specific plan you are leaving, 1-800-MEDICARE at 1-800-633-4227, TTY 1-877-486-2048, is the number the government gives.
What is not left uncertain is the other end of the change. The date your new coverage starts is fixed by rule, and it is not the date you decided.
When does new coverage start?
If you change during Medicare Open Enrollment, October 15 to December 7, your new coverage starts January 1 of the next year, and the plan must have your request by December 7. Changes made through the January to March window start the first of the month after the plan gets your request.
The gap between those two rules is the practical difference. One is a fixed date for everybody. The other moves with the arrival of your paperwork.
Whichever applies, the penalty rule runs underneath. Going 63 days or more in a row without Medicare drug coverage or other creditable drug coverage after you were eligible can bring a lifetime late enrollment penalty.
And that penalty follows the person rather than the plan. Medicare.gov states you pay it for as long as you have Part D coverage, even if you switch plans, so changing plans later does not clear it.
What this means for you
Changing a drug plan is a calendar question with a drug question inside it. The calendar decides whether you may act, and your own prescription list decides whether you should. Medicare Open Enrollment runs October 15 to December 7, and new coverage from it starts January 1.
Look every year even if nothing about your health changed. The drug list can move, tiers can move, and a plan can leave Medicare, all without you doing anything.
Compare on your own drugs rather than on premiums, and check the network and the coverage before the price. Then act inside the window, and remember the plan must receive the request before it closes.
For the windows themselves, read this publication's enrollment windows articles. For what a Part D penalty costs and how it is calculated, read the article on the Part D late enrollment penalty.
FAQ
Can I change my Medicare drug plan in the middle of the year?
Only through a Special Enrollment Period. Medicare.gov states that you can only join, switch or drop a Medicare drug plan at certain times, called enrollment periods, and it names Special Enrollment Periods as varying and applying only to certain situations that happen in your life.
The examples it gives are moving to a new address, losing or changing your current coverage, getting Medicaid, and getting Extra Help to pay drug costs.
Outside those, the two general windows are Medicare Open Enrollment, October 15 to December 7, and for people already in a Medicare Advantage plan, January 1 to March 31. Each has its own article in this publication, which is where the qualifying conditions are set out properly.
Do I have to cancel my old drug plan before joining a new one?
The pages read for this article do not say, and this one will not guess at it. What Medicare.gov does describe is the joining side: you select Enroll for the plan you want at Medicare.gov/plan -compare, contact the plan directly, or call 1-800-MEDICARE at 1-800-633-4227, TTY 1-877-486-2048.
It also describes one situation where joining a drug plan has a consequence for other coverage: a Medicare Advantage plan can disenroll you for several reasons, and joining a drug plan is one of them in some cases. If you want a definite answer about the specific plan you hold, 1-800-MEDICARE is the number the government gives for exactly that.
What is a formulary?
A formulary is a plan's list of covered drugs, and each plan has its own. Medicare.gov states that all plans must cover a wide range of prescription drugs that people with Medicare take, and that each drug list includes at least 2 drugs in the most commonly prescribed categories and classes, though plans can choose which drugs they offer.
All plans must include most drugs in certain protected classes, which are cancer drugs, HIV/AIDS drugs, antidepressants, antipsychotics, anticonvulsants, and immunosuppressants for organ transplants. A drug list can include brand-name and generic drugs, and also original biological products and biosimilars. This is why two plans with similar premiums can cost one person very different amounts.
My drug moved to a higher tier. Can I do anything before the next window?
Medicare.gov describes a route that does not depend on the calendar. If your drug is in a higher tier and your prescriber thinks you need it rather than a similar drug in a lower tier, you or your prescriber can ask the plan for an exception to get a lower coinsurance or copayment.
More broadly, an exception is when a plan decides to cover a drug that is not on its list, or waives a coverage rule, and a tiering exception is when it charges a lower amount for a drug on its non-preferred tier.
You or your prescriber must request it, and your doctor or other prescriber must provide a supporting statement explaining the medical reason.
Why did my costs go up when I did not change anything?
Because the plan is allowed to change underneath you. Medicare.gov states that a Medicare drug plan can make changes to its drug list during the year under guidelines set by Medicare, and that plans can change their drug list at any time.
It also names two specific ways your own cost can rise. Your coinsurance may increase for a drug when the manufacturer raises the price.
And your copayment or coinsurance may increase if you keep taking a brand name drug or original biological product after the plan adds a generic or biosimilar version and moves the brand to a higher cost-sharing tier. The plan must notify you of drug list changes that affect drugs you take.
Does switching plans reset my Part D late enrollment penalty?
No. Medicare.gov states that in most cases you pay the monthly penalty for as long as you have Part D coverage, even if you switch plans.
The penalty exists if you did not join a drug plan when you first got Medicare and went 63 days or more in a row without Medicare drug coverage or other creditable prescription drug coverage after you were eligible, and it goes up the longer you wait to join.
Creditable coverage means coverage expected to pay, on average, at least as much as Medicare drug coverage, and your current plan must tell you whether yours qualifies.
So the penalty is not a reason to stay in a plan that no longer fits. It follows you either way, and the drug list will keep moving whether or not you are watching it.
