What Is Medicare Part D and How Does It Work?

Medicare Part D is the part of Medicare that helps pay for prescription medications. Private insurance companies approved by Medicare offer these plans. Coverage, premiums, and out-of-pocket costs vary by plan.

People can get Part D through a standalone prescription drug plan or a Medicare Advantage plan that includes drug coverage. Understanding these options can help beneficiaries compare costs, check medication coverage, and avoid potential enrollment penalties.

For 2026, Medicare Part D also has an annual out-of-pocket limit for covered prescription drugs. This limit can make a significant difference for people who take several medications or need expensive prescriptions. Medicare.gov provides current details about coverage and costs.

What Is Medicare Part D?

Medicare Part D is an optional prescription drug benefit available to people with Medicare who enroll in an eligible plan. It helps cover certain prescription medications used outside a hospital or other medical setting.

Medicare Part D differs from the other main parts of Medicare:

• Part A: Helps cover inpatient hospital care, skilled nursing facility care under qualifying conditions, and certain other services.
• Part B: Helps cover physician services, outpatient care, and certain medications administered in medical settings.
• Part C: Also called Medicare Advantage, this option provides Medicare-approved health coverage through private plans. Most plans include prescription drug coverage.
• Part D: Helps pay for covered prescription drugs through a separate drug plan or an eligible Medicare Advantage plan.

Original Medicare does not generally include routine outpatient prescription drug coverage. People with Original Medicare can add a standalone Part D plan to obtain that coverage.

Medicare Advantage plans often combine medical and prescription drug benefits. However, not every plan includes drug coverage. Medicare.gov explains the available coverage options.

How Does Medicare Part D Work?

Medicare Part D works through private insurance companies that contract with Medicare. These companies must follow federal program requirements, but their plans can differ in price and coverage.

When someone enrolls, the plan provides information about covered medications, participating pharmacies, cost-sharing rules, and any restrictions.

Three features are especially important.

1. Formularies

A formulary is the list of prescription drugs covered by a plan. Each plan maintains its own formulary, subject to Medicare requirements.

Plans commonly cover both generic and brand-name medications. However, they may place drugs in different pricing tiers.

A lower-tier medication generally costs less than a higher-tier medication. Some drugs may require prior authorization, step therapy, or quantity limits.

Before enrolling, beneficiaries can check whether their current prescriptions appear on the plan’s formulary.

2. Pharmacy Networks

Part D plans may have networks of pharmacies with different cost-sharing arrangements.

A preferred pharmacy may offer lower costs than a standard network pharmacy. Some plans also offer mail-order services.

Using a pharmacy outside the plan’s network may result in higher costs or limited coverage. Exceptions depend on the plan’s rules and the circumstances.

3. Cost Sharing

Beneficiaries may pay several types of expenses:

• Premium: The amount paid each month for the insurance plan.
• Deductible: The amount paid for covered medications before the plan begins sharing costs, when a deductible applies.
• Copayment: A fixed amount paid for a prescription.
• Coinsurance: A percentage of a medication’s cost.

The exact amounts depend on the plan, the medication, the pharmacy, and the beneficiary’s coverage stage.

How Can You Get Medicare Part D Coverage?

There are two main ways to obtain Medicare prescription drug coverage.

Option 1: A Standalone Prescription Drug Plan

People enrolled in Original Medicare can purchase a separate Part D plan from a Medicare-approved private insurer.

To join a standalone Medicare drug plan, a person generally must have Medicare Part A and/or Part B, meet the plan’s residency requirements, and satisfy applicable eligibility rules.

This option allows beneficiaries to keep Original Medicare while adding prescription drug coverage.

Option 2: A Medicare Advantage Plan With Drug Coverage

Many Medicare Advantage plans combine hospital, medical, and prescription drug benefits.

These plans may have different premiums, provider networks, drug formularies, and cost-sharing arrangements. Some plans offer additional benefits, but their availability and terms vary.

In most types of Medicare Advantage plans, beneficiaries cannot enroll in a separate Part D plan while remaining in that plan. Doing so can affect existing coverage.

Anyone considering a change should review the plan’s terms before enrolling.

How Much Does Medicare Part D Cost in 2026?

The cost of Medicare Part D depends on the plan and the prescriptions a person uses. Monthly premiums vary, and some beneficiaries must pay an additional income-related amount.

For 2026, Medicare’s standard Part D benefit includes a deductible of up to $615. After the deductible is met, the plan’s cost-sharing rules determine how much the beneficiary pays for covered prescriptions.

The standard benefit also has an annual out-of-pocket threshold of $2,100 for covered Part D drugs. Once a beneficiary reaches the applicable threshold, catastrophic coverage begins, and the beneficiary pays no additional cost sharing for covered Part D drugs for the remainder of the calendar year. Monthly premiums do not count toward this limit.

Actual plan terms may differ from the standard benefit design, and some beneficiaries qualify for additional assistance.

CMS’s 2026 Part D guidance explains these changes.

Example of How Costs Can Add Up

Suppose a beneficiary has a plan with a deductible and takes several covered prescriptions throughout the year.

At first, the beneficiary may pay the full negotiated cost of covered medications until meeting the deductible. Afterward, the plan shares eligible costs according to its coverage rules.

As qualifying out-of-pocket spending accumulates, the beneficiary moves through the applicable coverage stages. Once the 2026 out-of-pocket threshold is reached, the beneficiary no longer pays cost sharing for covered Part D drugs for the rest of that year.

This is a simplified example. Actual expenses depend on the plan, the medications, and which payments count toward the annual threshold.

When Can You Enroll in Medicare Part D?

Enrollment is limited to specific periods, although special circumstances may create additional opportunities.

Initial Enrollment Period

People generally can enroll in a Part D plan when they first become eligible for Medicare. The initial enrollment period is tied to their Medicare eligibility dates.

Reviewing drug coverage during this period can help prevent gaps in coverage and potential penalties.

Annual Open Enrollment

Medicare’s annual Open Enrollment Period runs from October 15 through December 7.

During this period, eligible beneficiaries can join, switch, or drop a standalone Medicare drug plan. They can also make certain changes to Medicare Advantage coverage.

Changes generally take effect on January 1 of the following year.

Special Enrollment Periods

Certain circumstances may allow beneficiaries to enroll in or change coverage outside the usual periods. Examples may include losing qualifying prescription drug coverage or becoming eligible for specific assistance programs.

Eligibility depends on the circumstances. The official Medicare enrollment guide explains the available options.

What Is the Medicare Part D Late Enrollment Penalty?

A late enrollment penalty may apply when someone goes 63 or more consecutive days without Medicare drug coverage or other creditable prescription drug coverage after becoming eligible.

Creditable coverage is prescription drug coverage expected to pay, on average, at least as much as standard Medicare drug coverage. Certain employer plans, union plans, TRICARE, and Veterans Affairs coverage may qualify.

The Part D penalty is generally calculated using 1% of the national base beneficiary premium for each full month without qualifying coverage. The amount is rounded and added to the monthly Part D premium.

For 2026, the national base beneficiary premium is $38.99.

For example, someone with 12 full uncovered months could face a monthly penalty of approximately $4.70, based on the 2026 calculation. The penalty generally continues for as long as the person has Medicare drug coverage, and its dollar amount can change annually.

People who qualify for Extra Help do not pay the Part D late enrollment penalty.

Before dropping existing prescription coverage, beneficiaries should confirm whether it is creditable and understand how changing plans may affect other insurance benefits. Medicare’s penalty guidance provides additional details.

Can You Get Help Paying for Medicare Part D?

Some beneficiaries qualify for programs that reduce prescription drug expenses.

Extra Help

Extra Help is a federal assistance program for eligible people with limited income and resources. It can reduce Part D premiums, deductibles, and other prescription drug costs.

Eligibility depends on applicable requirements. People can review the program through Medicare’s official Extra Help information.

Medicare Prescription Payment Plan

The Medicare Prescription Payment Plan allows participants to spread eligible out-of-pocket prescription drug costs across the calendar year.

The option is available through participating Medicare drug coverage arrangements, and participation is voluntary. Beneficiaries continue paying any applicable plan premiums.

This program changes when prescription expenses are paid. It does not reduce the total cost of medications or eliminate the underlying charges.

Details are available at Medicare.gov.

How to Compare Medicare Part D Plans

Plan premiums alone do not show the full cost of prescription coverage. Two plans with similar monthly premiums may cover different medications or charge different amounts at the pharmacy.

Before choosing a plan, compare these factors:

1. Covered medications: Confirm that your prescriptions appear on the plan’s formulary.
2. Total expected costs: Consider premiums, deductibles, copayments, and coinsurance.
3. Pharmacy access: Check whether your preferred pharmacy participates in the plan’s network.
4. Drug restrictions: Review prior authorization, step therapy, and quantity limits.
5. Annual changes: Check the plan’s updated coverage rules and costs for the coming year.
6. Existing insurance: Confirm how enrollment could affect employer, union, or other prescription drug coverage.
7. Financial assistance: Determine whether you qualify for Extra Help or another applicable program.

Medicare’s official Plan Finder allows users to compare available plans and estimated costs based on their location and prescriptions.

Bottom Line

Medicare Part D helps beneficiaries pay for covered prescription medications through private insurance plans approved by Medicare. People can obtain coverage through a standalone drug plan or a Medicare Advantage plan that includes prescription benefits.

The cost depends on premiums, deductibles, covered medications, pharmacy arrangements, and other plan rules. In 2026, the standard Part D deductible is $615, and the annual out-of-pocket threshold for covered Part D drugs is $2,100.

Before enrolling or changing coverage, review the plan’s formulary, total expected costs, and enrollment requirements. Official Medicare resources provide the most reliable information about available plans and current program rules.

Sources

• Medicare.gov — Drug Coverage Basics
• Medicare.gov — Part D Costs
• Medicare.gov — Enrollment Periods
• Centers for Medicare & Medicaid Services — Final 2026 Part D Redesign Program Instructions
• Medicare.gov — Extra Help
• Medicare.gov — Medicare Prescription Payment Plan

This article provides general information and is not individualized financial, legal, tax, insurance, or medical advice.