Medicare Part D: How Prescription Drug Coverage Actually Works
Updated: May 16
A Plain-English Guide to Prescription Drug Coverage in 2026
If you're new to Medicare, here's an inconvenient truth: Original Medicare (Parts A and B) does not cover most prescription drugs. To get prescription coverage, you need Medicare Part D — either as a standalone plan, or bundled into a Medicare Advantage plan.
And 2026 is the year Part D actually got easier to understand. The Inflation Reduction Act eliminated the dreaded "donut hole" coverage gap, capped your annual out-of-pocket spending at $2,100, and introduced a way to spread that out over the year. Here at LifeHelm, we'd rather you understand the system than fear it — so let's walk through how Part D works now and what it costs.
How to Get Part D Coverage
You have two ways to get prescription drug coverage through Medicare:
Standalone Part D plan (PDP) — adds prescription coverage to Original Medicare. You enroll separately and pay a separate premium.
Medicare Advantage plan with prescription coverage (MA-PD) — bundles Part A, Part B, and Part D into one plan from a private insurer.
Both are run by private insurers approved by Medicare. The cap, formulary rules, and consumer protections apply to both. The differences come from how you access care more broadly (Original Medicare vs. Medicare Advantage), not from how Part D itself works.
How Part D Costs Work in 2026
This is where most of the new rules live. Pay attention here.
The Three Stages
Until 2025, Part D had four payment phases. As of 2025, there are three:
Deductible stage. You pay 100% of your drug costs up to your plan's deductible. In 2026, the maximum deductible any Part D plan can charge is $615 — many plans set theirs lower, or at $0 for generics.
Initial coverage stage. Once you meet your deductible (if any), you pay a copay or coinsurance — typically 25% — on each prescription, and the plan pays the rest. You stay in this stage until your total out-of-pocket spending hits $2,100.
Catastrophic stage. Once your out-of-pocket spending reaches $2,100 for the year, your plan covers 100% of your covered drugs for the rest of the calendar year. You pay nothing more.
The old "donut hole" — that frustrating middle phase where you suddenly paid much more for the same drugs — is gone.
Premiums
You'll pay a monthly premium for your Part D plan in addition to any other Medicare premiums (like Part B). Premiums vary widely by plan and by region. A couple of figures to know:
The "national base beneficiary premium" is $38.99 in 2026. This number is used by Medicare to calculate the late enrollment penalty (more on that below), not to set your actual plan premium.
Part D IRMAA. If your modified adjusted gross income from two years ago exceeded the IRMAA thresholds (currently $109,000 for individuals, $218,000 for joint filers), you'll pay an income-related monthly adjustment in addition to your plan premium. The IRMAA goes directly to Medicare, not to your plan.
The $2,100 Out-of-Pocket Cap
This is the change that matters most for anyone with expensive prescriptions.
Once your true out-of-pocket spending on covered Part D drugs hits $2,100 in 2026 — counting your deductible, copays, and coinsurance — your plan pays 100% for the rest of the year. The cap was $2,000 in 2025 and is indexed for inflation each year.
What counts:
Your deductible
Copays and coinsurance on covered drugs
What doesn't count:
Your monthly plan premium
Drugs not covered by your plan's formulary
Drugs covered under Part B (like infused chemotherapy)
Manufacturer coupons or assistance (the discount is real, but only your actual out-of-pocket portion counts toward the cap)
The Medicare Prescription Payment Plan
The cap solves one problem, but not all of them. Even with a $2,100 cap, you could still owe a substantial amount in January if you fill an expensive prescription early in the year. That lump-sum shock is real on a fixed income.
The Medicare Prescription Payment Plan (sometimes called "M3P" or "smoothing") lets you spread your Part D out-of-pocket costs across monthly bills from your plan, instead of paying at the pharmacy counter. You pay the same total — there's no interest or fees — but the burden is spread evenly across the year.
It's optional, it's free, and you can join before the plan year starts or any time during the year. If you miss a monthly bill, you can be removed from the program, though your underlying Part D coverage continues.
What's New in 2026
Beyond the cap and the donut hole elimination, two other changes are now in effect:
Medicare drug price negotiation. Starting in 2026, Medicare has negotiated lower prices on 10 widely prescribed drugs, including Eliquis, Xarelto, Jardiance, and Januvia. If you take any of these, your share of the cost should drop. A second round of negotiated prices for additional drugs is coming in subsequent years.
Insulin and vaccines. Insulin is capped at $35 per month for a one-month supply (or 25% of the negotiated price, whichever is less). Adult vaccines recommended by the CDC's Advisory Committee on Immunization Practices — including shingles, RSV, and Tdap — are covered with no cost-sharing.
Formularies, Tiers, and Why They Matter
Every Part D plan has a formulary — its list of covered drugs. No two formularies are identical, and the formulary can change from year to year. Plans organize their formulary into tiers, with each tier carrying a different cost:
Tier 1: Preferred generics — lowest cost
Tier 2: Generics
Tier 3: Preferred brand-name drugs
Tier 4: Non-preferred drugs — significantly higher cost-sharing
Tier 5: Specialty drugs — often coinsurance rather than copays
A drug's tier dictates what you'll pay. The same medication can be tier 2 on one plan and tier 4 on another. This is why "best plan" is meaningless without knowing which medications you actually take.
When you compare Part D plans, look up each of your prescriptions in each plan's formulary. Medicare.gov's Plan Finder will do this automatically if you enter your drug list.
Enrollment Windows and the Late Enrollment Penalty
The same enrollment windows apply for Part D as for the rest of Medicare:
Initial Enrollment Period. Seven months around your 65th birthday — three months before, the month of, and three months after.
Annual Enrollment Period (Open Enrollment). October 15 to December 7 each year. Switch plans, switch from standalone to MA-PD, or vice versa.
The late enrollment penalty is real and permanent. If you go 63 days or more without creditable drug coverage (Part D, or employer coverage at least as good as Part D), Medicare adds a penalty to your monthly Part D premium for as long as you have Medicare. The formula:
1% × $38.99 (the 2026 national base beneficiary premium) × the number of full months you were uncovered, rounded to the nearest $0.10.
So 24 uncovered months means a 24% penalty: $38.99 × 0.24 = $9.40 per month, added permanently to your Part D premium. And the base premium adjusts each year, so the dollar amount of your penalty can rise even as the percentage stays fixed.
If you have creditable employer drug coverage, you're fine — no penalty when you later move to Part D. Keep the annual Notice of Creditable Coverage your employer sends you; you may need to prove it.
How to Pick the Right Plan
A practical checklist when comparing Part D plans during Open Enrollment:
Pharmacy: Is your preferred pharmacy in the plan's preferred network? Out-of-network pharmacies can cost meaningfully more.
Formulary check: Look up every prescription you take in the plan's formulary. Note the tier for each.
Total annual cost — not just premium. A $0-premium plan can cost more than a $40-premium plan once you factor in deductibles, tier 4/5 cost-sharing, and prior-authorization hassles.
Prior authorization and step therapy rules: Some plans require you to try a cheaper drug first before they'll cover the one you actually want.
Plan rating: Medicare assigns a 1–5 star rating to each plan; 4+ stars is a good baseline.
Medicare.gov's Plan Finder is the cleanest way to do this — it lets you enter your medications and pharmacy and compares total estimated annual cost across all plans in your ZIP code.
The Bottom Line
Part D used to be the most painful part of the Medicare maze. After the IRA reforms, it's still complicated, but it's no longer terrifying:
Three stages instead of four
Hard $2,100 cap on what you'll pay out of pocket
Monthly smoothing option for predictable bills
Real price reductions on common drugs starting 2026
The smartest move you can make is to review your Part D plan every Open Enrollment, even if you're happy with what you have. Formularies change. Prices change. Plans change. Five minutes in Medicare.gov's Plan Finder during October to December can save you hundreds.
Here's to a Part D experience that helps you get your medications without breaking your budget.
Sources
Medicare.gov, "How much does Medicare drug coverage cost?" medicare.gov/health-drug-plans/part-d/basics/costs
Medicare.gov, "Avoid late enrollment penalties." medicare.gov/basics/costs/medicare-costs/avoid-penalties
Centers for Medicare & Medicaid Services, "2026 Medicare Parts A & B Premiums and Deductibles" fact sheet (November 14, 2025)
Medicare Rights Center, Part D analysis and updates. medicarerights.org
