What Medicare Part D is and when you can sign up

Medicare Part D is prescription drug coverage run by private insurance companies approved by Medicare. It helps pay for medications you take at home. You do not have to take it, but if you go without coverage for a long time and then sign up later, you will pay a higher monthly premium for the rest of your life.

You can sign up during your Initial Enrollment Period, which is the seven-month window that starts three months before the month you turn 65 and ends three months after. If you miss this window, you can still sign up during the general open enrollment period from October 15 to December 7 each year, but the late penalty applies unless you had other drug coverage in the meantime.

If you already have drug coverage through a current job or a former employer, you may not need Part D right away. But check with your plan administrator about whether it counts as "creditable coverage" — if it does not, you should sign up for Part D to avoid the penalty.

Key Takeaways

  • You sign up for Part D through Medicare.gov, by phone at 1-800-MEDICARE, or in person at your local Social Security office.
  • Part D plans vary widely in cost and which drugs they cover, so comparing plans before you choose matters for your specific medications.
  • Your coverage starts the first day of the month after you sign up, so timing your enrollment affects when protection begins.
  • If you miss your Initial Enrollment Period, you pay a penalty added to your premium each month unless you had other drug coverage.
  • You can change Part D plans once a year during open enrollment, even if you already have coverage.

Where to sign up and what information you need

You can enroll through three routes: Medicare.gov (the official Medicare website), by calling 1-800-MEDICARE, or by visiting your local Social Security office in person. Medicare.gov has a tool called the Plan Finder that shows you which Part D plans are available in your area and what each one costs for your specific medications — this is the fastest way to compare before you choose.

Before you start, gather your Medicare card, a list of all the medications you currently take (including the dose and how often you take them), and the pharmacies where you fill prescriptions. If you use mail order or specialty pharmacies, note those too. Having this information ready means the process takes 15 to 20 minutes instead of an hour.

When you call 1-800-MEDICARE, a representative will walk you through available plans and answer questions about costs and coverage. The line is open Monday through Friday, 8 a.m. to 8 p.m. Eastern Time. If you go to Social Security in person, bring your Medicare card and the same medication list.

Understanding Part D costs and how coverage works

Part D has four cost stages that change as you spend money on drugs. First is the deductible — the amount you pay out of pocket before the plan starts helping. Not all plans have a deductible, and deductibles vary. Second is the initial coverage period, where you and the plan split the cost of drugs (you pay your copay or coinsurance, the plan pays its share). Third is the coverage gap, sometimes called the "donut hole," where you pay more out of pocket until you reach a spending threshold. Fourth is catastrophic coverage, where the plan pays most costs after you have spent enough.

Each plan also has a monthly premium — the price you pay whether you use drugs or not. Premiums range widely depending on which drugs the plan covers and how much it charges for them. A plan with a low premium might charge high copays for your specific medications, while a plan with a higher premium might have lower copays. This is why using the Plan Finder to check costs for your actual drugs matters more than picking the cheapest plan.

Plans also have a formulary, which is the official list of drugs each plan covers. Before you sign up, check that all your current medications are on the formulary, or ask whether the plan will cover a similar drug instead. If your doctor prescribes a drug that is not covered, you can ask the plan for an exception, but this takes time and is not always approved.

Comparing plans and making your choice

The Medicare Plan Finder at Medicare.gov shows you every Part D plan available where you live, ranked by total estimated cost for your medications. Enter each drug you take, and the tool calculates what you would pay under each plan for a full year. This number includes the premium, deductible, copays, and coinsurance — everything except the catastrophic stage, which most people do not reach.

Look at more than just the lowest-cost option. Check whether your preferred pharmacy is in the plan's network (some plans charge more if you use an out-of-network pharmacy). Check whether your doctor's office or clinic can send prescriptions directly to the pharmacy, or whether you have to request them yourself. Check the plan's customer service phone number and hours — you may need to call if a drug is not covered or if you have questions about your bill.

If you take expensive medications or have a chronic condition that requires many drugs, look at plans that offer additional benefits beyond the basic Part D coverage. Some plans cover over-the-counter items like blood pressure monitors or diabetes supplies. Some offer programs that reduce copays for people with certain conditions. These extras are not available in every plan, so compare what is offered in your area.

What happens after you enroll

Once you sign up, Medicare sends you a confirmation letter with your plan name, member ID number, and the date your coverage starts. Your coverage begins on the first day of the month after you enroll. If you enroll on March 15, your coverage starts April 1. If you enroll on April 1, your coverage starts May 1. This timing matters if you are running low on medications — you may need to ask your doctor for an early refill or a larger supply to bridge the gap.

Your plan will mail you a pharmacy card before your coverage date. Use this card at any pharmacy in the plan's network. If you do not receive it by the time your coverage starts, call the plan's customer service number (on your confirmation letter) and ask them to send it again or give you a temporary number to use.

After your coverage starts, you can change plans once a year during the general open enrollment period (October 15 to December 7). If your current plan stops covering one of your drugs, or if your costs go up significantly, you can switch to a different plan. Changes made during open enrollment take effect January 1 of the following year.

What to do if you miss the enrollment important date

If you do not sign up during your Initial Enrollment Period and you do not have other drug coverage, you will pay a late enrollment penalty when you finally do sign up. The penalty is calculated as 1% of the national average Part D premium for each month you were without coverage. This amount is added to your monthly premium permanently — even if you switch plans later, the penalty stays.

The national average premium changes each year, so the penalty amount changes too. In 2024, the average was around $34 per month, meaning the penalty was roughly $0.34 per month of delay. If you waited two years to sign up, your penalty would be about $8 per month for life. This is why signing up during open enrollment, even if you do not think you need it yet, is usually worth doing.

The only way to avoid the penalty is to show that you had creditable drug coverage (coverage at least as good as Part D) during the time you were not enrolled. This includes coverage through a current job, a former employer, a union, TRICARE (military coverage), the Veterans Administration, or certain state programs. If you had this coverage, keep the paperwork proving it, because you may need to show it to Medicare later.

Frequently Asked Questions

Can I sign up for Part D if I have not turned 65 yet?

Yes, if you are already on Medicare for another reason — for example, because you have been on disability for two years or you have end-stage renal disease. Your Initial Enrollment Period starts three months before the month you become may be able to access for Medicare, not three months before you turn 65. If you are unsure when your period starts, call 1-800-MEDICARE.

What if my medications are not covered by any Part D plan in my area?

Call the plan and ask for an exception. The plan's pharmacy team can request that the drug be covered for you specifically, even if it is not on the standard formulary. This takes a few days to a week, and the plan may ask your doctor to confirm that you need this particular drug. If the exception is denied, you can appeal the decision.

Do I have to use the pharmacy my plan suggests?

No. You can use any pharmacy in the plan's network. Most large chains like CVS, Walgreens, and Rite Aid are in most plans' networks, but some smaller or independent pharmacies may not be. Before you sign up, check whether your current pharmacy is in the network, or be prepared to switch.

Can I change my Part D plan if my costs go up?

You can change plans during the general open enrollment period (October 15 to December 7) each year, regardless of whether your costs changed. If your plan stops covering a drug you need, you may also be able to change plans outside of open enrollment — call your plan to ask about a special enrollment period.

What if I cannot afford my Part D copays?

You may be able to get help through the Part D Low-Income Subsidy program, which reduces copays and premiums for people with limited income and resources. To learn whether you may have access to, contact your local Medicaid office or call 1-800-MEDICARE. Some pharmaceutical companies also offer patient information programs that cover copays for specific drugs.