Understanding Medicare Part D Prescription Drug Plans

What Is Medicare Part D?

Medicare Part D is the prescription drug benefit program that helps Medicare beneficiaries pay for outpatient prescription medications. Created by the Medicare Modernization Act of 2003, Part D coverage is offered through private insurance companies approved by Medicare.

You can get Part D coverage in two ways: through a stand-alone Prescription Drug Plan (PDP) that supplements Original Medicare, or through a Medicare Advantage plan that includes prescription drug coverage (MA-PD). Either way, the core Part D benefit structure and rules apply.

Part D is voluntary, but if you do not enroll when first eligible and do not have creditable drug coverage from another source, you will face a permanent late enrollment penalty.

How Part D Coverage Phases Work

Part D prescription drug coverage operates in distinct phases throughout the calendar year:

Deductible Phase: You pay the full cost of your drugs until you meet the annual deductible (up to $590 in 2026). Some plans have $0 deductibles or waive the deductible for certain drug tiers.

Initial Coverage Phase: After meeting the deductible, you pay copayments or coinsurance for your drugs. The plan pays its share. This phase continues until your total drug costs (what you and the plan pay combined) reach $5,030.

Coverage Gap: Thanks to the Inflation Reduction Act, starting in 2025, Medicare beneficiaries pay no more than $2,000 in total out-of-pocket prescription drug costs per year. This effectively eliminates the coverage gap (donut hole) that previously required significant out-of-pocket spending.

Catastrophic Coverage: After your out-of-pocket spending reaches the annual cap, you pay nothing for covered Part D drugs for the rest of the year.

Understanding Formularies and Drug Tiers

Each Part D plan has a formulary, which is a list of covered prescription drugs organized into tiers. Lower-tier drugs generally have lower costs, while higher-tier drugs cost more.

Typical drug tiers include:

• Tier 1: Preferred generic drugs (lowest cost, often $0-$15)
• Tier 2: Generic drugs ($5-$20 copay)
• Tier 3: Preferred brand-name drugs ($30-$50 copay)
• Tier 4: Non-preferred brand-name drugs (higher copay or coinsurance)
• Tier 5: Specialty drugs (typically 25-33% coinsurance)

Not all drugs are covered by every plan. Before enrolling, check each plan's formulary to ensure your medications are covered and note any quantity limits, prior authorization requirements, or step therapy protocols that may apply.

How to Choose a Part D Plan

Selecting the right Part D plan requires comparing several factors specific to your medication needs. Start by making a complete list of all your current prescriptions, including dosages and quantities.

Use the Medicare Plan Finder tool at Medicare.gov to enter your medications and compare plans available in your area. The tool estimates your total annual drug costs under each plan, including premiums, deductibles, and copays.

Key factors to compare include the monthly premium, annual deductible amount, whether your drugs are on the formulary, the copay or coinsurance for each of your drugs, preferred pharmacy network (using preferred pharmacies often saves money), mail-order options, and the plan's CMS star rating for quality.

Remember to re-evaluate your Part D plan every year during the Annual Enrollment Period, as formularies, premiums, and pharmacy networks change annually.

Extra Help and Cost Savings

Medicare's Extra Help program (also called the Low Income Subsidy or LIS) helps people with limited income and resources pay Part D costs. If you qualify, Extra Help can pay most or all of your Part D premiums, deductibles, and copays.

You may automatically qualify for Extra Help if you have full Medicaid coverage, receive Supplemental Security Income (SSI), or participate in a Medicare Savings Program. Others can apply through Social Security.

Additionally, the Inflation Reduction Act has significantly reduced Part D costs for all beneficiaries by capping annual out-of-pocket drug spending at $2,000, capping insulin costs at $35 per month, and eliminating cost-sharing in the catastrophic phase. These protections took full effect in 2025.