What Is Medicare Part D? A Guide to Prescription Drug Coverage

Medicare Part D helps pay for outpatient prescription drugs. It may be a stand-alone plan alongside Original Medicare or included in most Medicare Advantage plans. The lowest monthly premium is not necessarily the best plan for your medications and pharmacy.

1. Who Can Join?

Generally, a person with Medicare Part A or Part B who lives in the service area may join a stand-alone Part D plan. Medicare Advantage drug plans generally require both Part A and Part B.

2. What Drugs Are Covered?

Plans cover many generic and brand-name medicines but each has its own formulary and tiers. Lower tiers often cost less. Some adult vaccines covered under Medicare rules have no deductible or copay.

3. What Is Generally Not Covered?

Drugs outside the formulary, legally excluded drugs, medicines covered by Parts A or B, purchases outside pharmacy rules and most nonprescription vitamins and supplements may not be covered. You or your prescriber may request an exception or appeal when needed.

4. Key 2026 Costs

For 2026, the maximum Part D deductible is $615 and the annual out-of-pocket limit for covered Part D drugs is $2,100. After reaching the limit, covered Part D drug cost sharing is zero for the rest of that year. Premiums and noncovered drugs do not count toward the $2,100. Higher-income beneficiaries may owe Part D IRMAA. These figures apply to 2026, not automatically to later years.

5. Formulary Rules

Check each drug's exact name, strength, form and frequency. A plan can require prior authorization, step therapy or quantity limits, and may use specialty tiers. Being listed does not necessarily mean a drug is inexpensive.

6. Pharmacy Networks

A preferred pharmacy may cost less than a standard in-network pharmacy. Compare local and mail-order options and 30- and 90-day supplies, considering future travel or moves.

7. Enrollment and Changes

Initial enrollment is generally available when first eligible. Medicare Open Enrollment from October 15 through December 7 generally permits changes for the next year. A move or loss of creditable drug coverage may trigger a special enrollment period.

8. Late Enrollment Penalty

Going 63 consecutive days or longer without Part D or other creditable prescription coverage after eligibility may result in a penalty, generally calculated by full uncovered months and potentially lasting while you have Part D. Keep annual creditable-coverage notices.

9. Extra Help and Payment Spreading

Extra Help can reduce premiums, deductibles and drug costs for eligible people; some Medicaid or Medicare Savings Program participants qualify automatically, while others may apply through Social Security. The Medicare Prescription Payment Plan spreads eligible out-of-pocket drug costs over months; it is not a discount and does not reduce total costs.

10. Compare Each Year

List medications, strengths, forms and frequency; check formularies, tiers, restrictions and preferred pharmacies; then compare premiums, deductibles and estimated annual costs. Recheck each year.

This is general education, not legal, tax, medical or individual insurance advice. Costs and formularies change annually; verify current information in Medicare Plan Finder and plan documents.