Medicare Part D in 2026: Costs, IRMAA, and the Late Penalty Most People Don't Expect

Part D prescription drug coverage looks straightforward until you add IRMAA surcharges, the late enrollment penalty, and HSA conflicts. Here's the complete picture for retirees with meaningful income.

2026 Part D cost structure

Every Part D plan has four cost layers. You pay through each in order until you hit the out-of-pocket cap, at which point Medicare covers 100% of drug costs for the rest of the year.

The out-of-pocket cap is $2,100 in 2026, up from $2,000 in 2025.¹ This cap was created by the Inflation Reduction Act of 2022 and eliminates what used to be the "donut hole" coverage gap. Once you've spent $2,100 on covered drugs — counting your deductible, coinsurance, and any costs in what was formerly the gap — you pay nothing for covered drugs for the rest of the calendar year.

Your monthly plan premium is separate and does not count toward the OOP cap. The national average standalone Part D premium is approximately $34.50/month in 2026,² though plans range from near-zero to $80+/month depending on formulary and region. Medicare Advantage plans frequently bundle Part D coverage; if yours does, you won't have a separate Part D premium.

Part D IRMAA: the surcharge tied to your income

If your income exceeds certain thresholds, Social Security adds an IRMAA surcharge to your Part D costs — the same two-year look-back that governs Part B IRMAA. Your 2026 Part D surcharge is based on your 2024 MAGI (adjusted gross income plus tax-exempt interest).

The surcharge is paid directly to Medicare, not to your Part D plan or insurer. You receive a monthly bill from Social Security. This surprises many beneficiaries who only look at plan premiums when budgeting for drug costs.

The brackets are the same thresholds that apply to Part B IRMAA — the income tier determines both surcharges simultaneously. If you're in Tier 3 for Part B, you're in Tier 3 for Part D. Use the IRMAA bracket calculator to see both surcharges together for your income level.

The one-year spike problem

A Roth conversion, business sale, or large capital-gain event in 2024 can push your MAGI over an IRMAA tier for just one year — but you'll pay elevated Part D (and Part B) premiums for all of 2026. If your income has since returned to a lower level due to a qualifying life event (retirement, reduction in work hours, loss of a pension), you may be able to file an appeal using Form SSA-44 to substitute 2025 income instead. If the spike was a one-time event without a qualifying life event, there's no formal appeal path — but the surcharge is temporary and disappears once the lower-income year becomes the look-back year.

This is one of the core reasons retirees work with a Medicare-specialist advisor: Roth conversions, capital-gain harvesting, and required minimum distributions all create MAGI, and each has a two-year delayed price tag in the form of Part D and Part B surcharges. See our full guide on Roth conversions and IRMAA for the bracket cliff math.

The late enrollment penalty — permanent and compounding

If you don't enroll in Part D when you first become eligible (and don't have other creditable drug coverage), Medicare imposes a late enrollment penalty that stays with you for life.

Formula: 1% × $38.99 (2026 national base beneficiary premium) × number of full uncovered months = monthly penalty amount, rounded to nearest $0.10.³

The penalty clock starts 63 days after your Initial Enrollment Period ends (typically 63 days after the month you turn 65, unless you delayed Medicare enrollment due to active employer coverage). A continuous gap of 63 days or more without creditable coverage is what triggers it.

What counts as creditable coverage: Employer group health plans with drug benefits that are "actuarially equivalent" to Medicare's standard Part D benefit typically qualify. Your employer's HR department or benefits carrier can confirm in writing. COBRA, retiree group coverage, and VA drug benefits also typically qualify. The key is to get written confirmation — without it, SSA may assess a penalty anyway and you'll have to appeal.

Part D and HSA contributions: a critical conflict

Enrolling in any part of Medicare — including Part D — disqualifies you from contributing to a Health Savings Account. If you're still working past 65, have an HSA-eligible high-deductible health plan through your employer, and want to keep contributing to your HSA, you must avoid Part D enrollment until you retire.

Part A retroactive enrollment creates a parallel trap: when you claim Social Security, Medicare Part A is automatically activated — and Part A can be backdated up to 6 months. If that backdated start date overlaps with an HSA contribution, those contributions become ineligible and subject to income tax plus a 6% excise tax. See the full analysis in our Medicare and HSA guide.

Choosing a Part D plan: what actually matters

Most people focus on monthly premium, but for anyone taking expensive specialty drugs, the formulary and cost-sharing structure matter far more. Here's what to evaluate:

• Formulary tier for your drugs: The same medication can sit on tier 1 (generic, low copay) at one plan and tier 4 (specialty, 25–33% coinsurance) at another. Check every plan's actual formulary at Medicare.gov Plan Compare before enrolling.
• Pharmacy network: Preferred pharmacy networks give lower cost-sharing at specific chains. If you use a mail-order pharmacy, verify the plan works with it.
• Deductible: Plans can waive or reduce the standard $615 deductible for some tiers (commonly generics). If your drugs are generics, a zero-deductible plan may cost less overall even with a higher premium.
• OOP cap applies to formulary drugs only: The $2,100 cap counts spending on covered (formulary) drugs. Off-formulary drugs don't count toward it. Know which tier your key medications sit on.

The Medicare Plan Compare tool at medicare.gov takes your exact drug list and zip code and calculates estimated annual costs across all available plans. Run this calculation every fall during the Annual Enrollment Period (October 15 – December 7) because plans change formularies and premiums each year. The plan you enrolled in three years ago may no longer be optimal for your current drug list.

Annual Enrollment Period: your reset window

Unlike Medigap, which has medical underwriting outside the initial enrollment window, Part D has full annual flexibility. Every year from October 15 through December 7, you can switch, drop, or add a Part D plan with no health questions. Changes take effect January 1.

This means the late enrollment penalty is the only permanent downside of Part D decisions — the plan itself can be optimized year-over-year. High earners who are managing Roth conversions or other income events that affect IRMAA should revisit their plan choices annually as their projected drug costs and IRMAA exposure change.

When to involve a Medicare-specialist advisor

A generalist financial advisor often views Medicare as "the insurance people handle that separately." But Part D costs interact directly with:

• Roth conversion timing — conversion income in 2024 sets your 2026 Part D surcharge
• IRMAA appeal eligibility — if retirement or a life event dropped your income in 2025 or 2026
• HSA contribution strategy — delaying Part D to maximize HSA contributions pre-retirement
• RMD timing — required minimum distributions count as MAGI and can push you across a Part D IRMAA tier

Modeling these interactions requires running Medicare costs alongside your income strategy, not in a separate silo. That's what a Medicare-specialist advisor does differently.

1. CMS, "Final CY 2026 Part D Redesign Program Instructions," cms.gov/newsroom — 2026 Part D deductible cap $615, OOP cap $2,100, effective 2026 plan year.
2. CMS, "2026 Medicare Parts A & B Premiums and Deductibles," cms.gov/newsroom — average standalone Part D total premium projected at $34.50/month for 2026.
3. Medicare.gov, "Avoid late enrollment penalties" — Part D late enrollment penalty formula: 1% × national base beneficiary premium ($38.99 in 2026) × uncovered months.
4. Kiplinger / Humana, 2026 IRMAA Part D surcharge tiers — $14.50 / $37.50 / $60.40 / $83.30 / $91.00 per month, based on CMS 2026 premium announcement. Income thresholds based on 2024 MAGI.

Values verified against CMS and Medicare.gov as of April 2026.