Medicare Part D is prescription drug coverage you add to Original Medicare or a Medicare Advantage plan

Medicare Part D is a separate insurance policy that covers prescription medications. It is not automatic — you must choose a plan and enroll during a specific window, or you may face a permanent penalty on your premiums. Part D is offered by private insurance companies approved by Medicare, not by Medicare itself.

You can add Part D to Original Medicare (Parts A and B) at any time. If you have a Medicare Advantage plan (Part C), that plan usually includes prescription coverage already, though you can switch to Original Medicare plus a separate Part D plan during the annual enrollment period. The cost, covered drugs, and pharmacies vary by plan and by year.

Key Takeaways

  • You must enroll in Part D during your Initial Enrollment Period (usually when you first turn 65) or during the annual enrollment period (October 15 to December 7 each year) to avoid a lifetime penalty.
  • Part D plans are sold by private insurers and cover different drugs at different costs, so comparing plans before you enroll matters — the cheapest plan today may not cover your specific medications.
  • You can enroll through Medicare.gov, by calling 1-800-MEDICARE, or by contacting an insurance agent or your local Area Agency on Aging.
  • If you miss your enrollment window and have no other creditable coverage, you will pay a permanent surcharge on top of your monthly premium for as long as you have Part D.

When you can enroll in Part D

Your Initial Enrollment Period is the seven-month window centered on the month you turn 65. It starts three months before your birthday month and ends three months after. If you enroll during this window, your coverage begins on the first day of the month you turn 65 (or the month after, depending on when you enroll). This is the easiest time to enroll without penalty.

If you miss your Initial Enrollment Period, you can enroll during the Annual Enrollment Period, which runs October 15 through December 7 each year. Coverage begins January 1 of the following year. You can also switch plans during this window if you are already enrolled in Part D.

Outside these windows, you can only enroll if you have a may have access to life event — such as loss of other drug coverage, a move out of your plan's service area, or Medicaid loss. You must report the event to Medicare within 60 days to enroll without penalty.

How to compare and choose a Part D plan

Part D plans differ in three main ways: monthly premium, which drugs they cover, and which pharmacies you can use. A plan with a low premium may not cover the medications you take, or may require you to pay more out of pocket for them. The plan that costs least overall depends on your specific prescriptions.

Use the Medicare Plan Finder tool at Medicare.gov to compare plans in your area. Enter your zip code and the medications you currently take (include the dose and quantity). The tool shows each plan's monthly premium, your estimated yearly out-of-pocket costs for those drugs, and which pharmacies are in-network. You can sort by total cost, not just premium.

If you do not have internet access or need help using the tool, call 1-800-MEDICARE (1-800-633-4227). A representative can walk you through the comparison over the phone, or you can visit your local Social Security office or Area Agency on Aging for in-person help.

Documents and information you will need to enroll

You do not need to gather many documents to enroll in Part D. Have your Medicare card handy — it shows your Medicare number. You will also need a list of your current medications, including the name, dose, and how often you take each one. If you do not know the exact dose, your pharmacy can print a list for you.

If you are enrolling through an insurance agent or broker, they may ask for your Social Security number and date of birth to verify your identity. You do not need to provide bank account information or pay anything upfront during enrollment — the plan will bill you monthly after coverage begins.

The three ways to enroll

Online through Medicare.gov: Go to Medicare.gov, click "Enroll in a plan," and follow the steps. You will enter your zip code, select a plan from the comparison results, and confirm your enrollment. You should receive a confirmation email and a welcome packet from the insurance company within two weeks. This method is fastest if you are comfortable online.

By phone: Call 1-800-MEDICARE (1-800-633-4227). A representative will help you compare plans, answer questions, and enroll you over the phone. The call is free. Have your Medicare card and medication list ready. Enrollment usually takes 15 to 30 minutes.

Through an insurance agent or broker: You can contact a local insurance agent who sells Medicare plans, or ask your doctor's office or pharmacy if they have a recommendation. Agents can meet you in person, help you compare plans, and submit your enrollment. They are paid by the insurance company, not by you — there is no extra cost to use an agent. Your local Area Agency on Aging can also connect you with enrollment counselors.

What happens after you enroll

After you enroll, the insurance company will send you a welcome packet with your member ID card, plan documents, and a list of covered drugs (called the formulary). This usually arrives within two weeks. Your coverage begins on January 1 if you enrolled during the annual period, or on the first of the month you turn 65 if you enrolled during your Initial Enrollment Period.

Before your coverage starts, review the formulary to confirm your medications are covered. If a drug is not on the list, contact the plan to ask about coverage options — some plans will cover an uncovered drug if your doctor requests an exception. If your plan does not cover a medication you need, you can switch to a different plan during the next annual enrollment period.

Once coverage begins, use your member ID card at any pharmacy in the plan's network. You will pay a copay or coinsurance for each prescription, depending on the plan and the drug. The plan will track your spending and send you updates as you approach the coverage gap (a cost-sharing phase that applies to some plans) and catastrophic coverage.

The penalty for late enrollment

If you do not enroll in Part D when you are first may be able to access and you do not have other creditable prescription drug coverage, you will pay a late enrollment penalty for as long as you have Part D. The penalty is calculated based on how many months you went without coverage, and it increases your monthly premium permanently.

The penalty amount changes each year. For 2024, it is roughly 1% of the national average Part D premium per month of delay. If you delayed for two years, for example, your penalty would be about 24% of the average premium, added to your plan's base premium every month. This penalty does not go away if you switch plans later.

The only way to avoid the penalty is to have had creditable coverage — prescription drug coverage as good as or better than Medicare Part D — from another source during the gap. This might be coverage through a current or former employer, a union, TRICARE, the Veterans Administration, or a state Medicaid program. If you had creditable coverage, keep proof of it (a letter from that plan or employer) in case Medicare questions your enrollment later.

Frequently Asked Questions

Can I enroll in Part D if I already have a Medicare Advantage plan?

Most Medicare Advantage plans include prescription drug coverage, so you do not need a separate Part D plan. If your Advantage plan does not include drug coverage (rare), you can add Part D. If you want to switch from an Advantage plan to Original Medicare, you can add a separate Part D plan during the annual enrollment period or within 63 days of leaving the Advantage plan.

What if my medication is not covered by the plan I chose?

Contact the plan and ask about a formulary exception. Your doctor can request that the plan cover the drug anyway, especially if you have tried other drugs on the formulary and they did not work. The plan must respond within 72 hours. If the exception is denied, you can appeal or switch to a different plan during the next annual enrollment period.

Do I have to use a pharmacy in the plan's network?

Most plans charge much less if you use an in-network pharmacy. You can use an out-of-network pharmacy, but you will pay more out of pocket and may have to pay upfront and request reimbursement. Check the plan documents to see which pharmacies are in your area before you enroll.

What if I cannot afford the monthly premium?

You may be able to get help paying Part D premiums through the Low-Income Subsidy program (also called Extra Help) if your income is below a certain level. Contact your local Social Security office or call 1-800-772-1213 to learn whether you may have access to. You can also ask the insurance company about payment plans.

Can I change my Part D plan after I enroll?

You can change plans once per year during the annual enrollment period (October 15 to December 7). If you have a may have access to life event, such as loss of other coverage or a move, you can change plans outside the annual period. Contact Medicare or your current plan to request a change.