The Medicare Part D prescription drug landscape looks meaningfully different in 2026 than it did just two years ago, and the single biggest reason is a $2,000 annual out-of-pocket cap on covered drugs. That limit, phased in under the Inflation Reduction Act, eliminates the coverage gap — the so-called donut hole — that forced millions of beneficiaries to pay full drug costs for months each year. For anyone taking expensive specialty medications for cancer, rheumatoid arthritis, or multiple sclerosis, this change can translate into thousands of dollars in annual savings.
But the cap doesn't mean all Part D plans are now equal. Insurers have responded to the new cost structure by adjusting premiums, formularies, and pharmacy networks in ways that vary significantly from plan to plan and state to state. In 2026, the national average monthly premium for a standalone Part D prescription drug plan (PDP) sits around $46, according to CMS data, but individual plan premiums range from under $10 to well over $100 depending on the insurer and region. A low premium can be misleading if the plan places your medications on a high cost-sharing tier or excludes your preferred pharmacy from its preferred network.
When evaluating Part D plans, the most important starting point is your personal medication list. Medicare's Plan Finder tool, available at Medicare.gov, allows you to enter every drug you take — including dosage and frequency — and compare your estimated annual costs across every plan available in your ZIP code. This total cost estimate, not the monthly premium, is the number that matters. A plan charging $35 per month may cost you far less overall than a $12-per-month plan if the cheaper option places your blood thinner or diabetes medication on a non-preferred tier with a $100 copay per fill.
Formulary tiers are the architecture of cost-sharing inside any Part D plan. Most plans use a five-tier structure: Tier 1 covers preferred generics at the lowest copay (often $0–$5), Tier 2 covers non-preferred generics, Tier 3 covers preferred brand-name drugs, Tier 4 covers non-preferred brands, and Tier 5 covers specialty drugs. Under the $2,000 cap, even Tier 5 specialty drugs are now capped annually, but your monthly cost-sharing before hitting that cap can still be substantial — often 25–33% of the drug's cost. Plans that place your specialty drug on Tier 5 versus Tier 3 can mean hundreds of dollars in monthly costs until you reach the cap.
Pharmacy network design is another variable that catches beneficiaries off guard. Most Part D plans distinguish between preferred and non-preferred pharmacies, with meaningfully lower cost-sharing at preferred locations. Major chains like CVS, Walgreens, and Walmart are preferred in many plans, but not all — and mail-order pharmacies, which typically offer 90-day supplies at reduced cost, vary by plan as well. If you rely on an independent community pharmacy, verify its network status before enrolling.
For beneficiaries enrolled in Medicare Advantage (Part C) plans, drug coverage is typically bundled into the MA-PD plan rather than purchased separately. In 2026, the same $2,000 out-of-pocket cap applies to drug costs within MA-PD plans, but the cap is separate from the plan's medical out-of-pocket maximum. Comparing an MA-PD plan to a standalone PDP paired with Original Medicare requires looking at both drug and medical cost-sharing together.
Low-income beneficiaries should also check their eligibility for the Extra Help program (also called the Low Income Subsidy), which in 2026 provides full premium subsidies and near-zero cost-sharing for Part D enrollees below roughly 150% of the federal poverty level. CMS expanded Extra Help eligibility in recent years, and many beneficiaries who previously didn't qualify may now be eligible. Applications are accepted year-round through the Social Security Administration at ssa.gov.
The Annual Enrollment Period — October 15 through December 7 — is the primary window to switch Part D plans, with coverage beginning January 1. If you miss AEP, the Open Enrollment Period from January 1 through March 31 allows Medicare Advantage enrollees to switch plans or return to Original Medicare with a standalone PDP. Outside these windows, changes are generally limited to qualifying Special Enrollment Period events such as moving to a new service area or losing other creditable drug coverage. Reviewing your plan each fall is worth the hour it takes — formularies, premiums, and pharmacy networks can all change on January 1, even if you do nothing.