Medicare Part D helps pay for outpatient prescription drugs. It is not included in Original Medicare automatically, so people using Original Medicare usually need to choose a stand-alone Part D plan if they want drug coverage. Most Medicare Advantage plans include Part D.

What Does Part D Cover?

Every Part D plan has a formulary, or list of covered drugs. Medicare sets coverage standards, but formularies vary.

Plans commonly group drugs into tiers:

  • Lower-cost generic drugs
  • Preferred brand-name drugs
  • Non-preferred drugs
  • High-cost specialty drugs

A drug’s tier affects what you pay. A copayment is a fixed amount; coinsurance is a percentage of the cost. Plans may require approval before the plan pays for a prescription, called prior authorization. They may also require you to try another drug first, called step therapy, or limit how much you can get at once. You or your prescriber can request an exception when there is a medical reason.

How Do You Get Part D?

A stand-alone Part D plan generally requires Part A or Part B; Medicare Advantage requires both. You must also meet the plan’s other enrollment conditions. There are two main routes:

  1. Add a stand-alone Part D plan to Original Medicare.
  2. Join a Medicare Advantage plan that includes drug coverage.

In most HMO and PPO Medicare Advantage plans, you cannot add a separate Part D plan. Doing so may end your Medicare Advantage enrollment and return you to Original Medicare.

What Does Part D Cost in 2026?

Costs vary by plan and can include a monthly premium, deductible, copayments, and coinsurance. In 2026:

  • No Part D plan may have a deductible above $615.
  • Your annual out-of-pocket spending for covered Part D drugs is capped at $2,100.
  • After reaching that cap, you pay no copayment or coinsurance for covered Part D drugs for the rest of the year.

Higher-income members may pay an income-related adjustment in addition to the plan premium.

If an expensive covered prescription creates a large bill early in the year, the Medicare Prescription Payment Plan can spread payments through the remaining months. It changes when you pay, not the total cost. Extra Help is a separate program that can reduce costs.

How to Compare Plans

Do not compare premiums alone. Enter every prescription, dosage, and preferred pharmacy into Medicare Plan Compare. Check:

  • Whether each drug is covered
  • Its tier and restrictions
  • The annual deductible
  • Preferred versus standard pharmacies
  • Estimated total annual cost
  • Mail-order options

Recheck during Open Enrollment because formularies and costs can change each year.

For an example comparing plans with the same medication list, see how to compare Part D plans.

Can You Be Penalized for Waiting?

You may owe a Part D late-enrollment penalty if you go 63 consecutive days or more without Part D or other creditable prescription coverage after your Initial Enrollment Period ends. Creditable coverage is expected to pay, on average, at least as much as standard Medicare drug coverage.

Keep creditable-coverage notices from an employer, union, or other plan.

Medicare policy sources last checked: October 8, 2026.