Part D is Medicare's outpatient prescription drug benefit, delivered either through a standalone Prescription Drug Plan (PDP) alongside Original Medicare or bundled into a Medicare Advantage plan (MA-PD). Every plan uses a formulary organized into cost-sharing tiers, and every plan is regulated by CMS.
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The 2025 structure
- Deductible: up to $590 (plans may charge less).
- Initial coverage: you pay tier-based cost-sharing (copays or coinsurance).
- Annual out-of-pocket cap: $2,000. After you hit it, covered drugs are $0 for the rest of the calendar year.
- Coverage gap ("donut hole"): eliminated as a distinct phase.
Medicare Prescription Payment Plan
New in 2025: enrollees can elect to spread their annual Part D out-of-pocket costs across monthly installments through their plan rather than paying at the pharmacy counter. This is most useful for people with a large early-in-year cost (e.g. a $1,200 specialty fill in January) they'd rather spread over 12 months. Opt in through the plan; there is no interest or fee.
Formularies and tiers
Every plan publishes a formulary — the list of covered drugs and their tier. Tiers typically range from Tier 1 (preferred generic, lowest copay) to Tier 5 (specialty, coinsurance often 25–33%). A plan can change its formulary during the year with 30 days' notice, subject to CMS rules.
The late-enrollment penalty
If you go 63 or more consecutive days without creditable prescription drug coverage after your Initial Enrollment Period, you'll owe a permanent penalty when you eventually enroll. The penalty is 1% of the national base beneficiary premium ($36.78 in 2025) per uncovered month, added to your Part D premium for life. Employer, VA and Tricare coverage typically qualify as creditable — get written confirmation from the plan sponsor.
How to pick a plan each fall
- List every prescription with dosage and refill frequency.
- Enter the list into Medicare's Plan Finder for your ZIP, including your preferred pharmacies.
- Compare total annual cost — premium plus drug cost-sharing — not just premium.
- Confirm each drug is on the formulary at a tier you can afford, with no utilization management (prior authorization, step therapy) that surprises you.
- Re-shop every year during the Annual Election Period. Plans, prices, and formularies change.