Medicare Part D Costs Explained: Tiers, the Coverage Gap and the $2,100 Cap

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The Coverage Gap You Remember Doesn’t Exist Anymore

If you last studied Part D closely around 2019, you probably remember the donut hole. You paid a deductible, then roughly a quarter of your drug costs, then — somewhere in the middle — the plan stopped helping and your share jumped. People split tablets in that zone.

That gap is closed. Honestly, it is the biggest change to Medicare drug costs in decades, and plenty of people still haven’t heard. As of 2025 the benefit has three stages: deductible, initial coverage, catastrophic. No middle stretch where your costs spike.

What replaced it is a hard ceiling. In 2026 you will not pay more than $2,100 out of pocket for drugs your plan covers, and once you reach that number you pay $0 for the rest of the calendar year — a threshold CMS confirmed in its 2026 Part D redesign instructions.

One thing to be clear about: $2,100 is the 2026 figure only. It was $2,000 last year, and CMS has published $2,400 for 2027. The cap is indexed annually — check the current number rather than memorizing it.

The Three Stages Your Prescriptions Move Through in 2026

Stage one — the deductible. No Part D plan may charge a deductible above $615 in 2026, and many charge nothing at all. Until you have spent that amount, you pay the plan’s full negotiated price.

Stage two — initial coverage. After the deductible you pay 25% coinsurance on covered drugs. This stage now runs all the way to the cap. Under the old rules it ended early and dropped you into the gap — that is what changed.

Stage three — catastrophic coverage. Once your true out-of-pocket spending hits $2,100, you pay nothing for covered Part D drugs for the rest of the year. Not a reduced copay. Zero.

Your monthly premium keeps arriving whichever stage you are in, and the cap does not touch it. Premium plus out-of-pocket is the real annual figure — see how that sits alongside your other coverage on my insurance planning page.

A Worked Example: What a $640 Monthly Pharmacy Bill Actually Costs You

Percentages on a screen don’t land. Let me run one set of numbers through.

Picture a $640 monthly pharmacy bill — one specialty drug plus two or three maintenance prescriptions gets you there. To keep the arithmetic honest I’ll assume a plan with the maximum $615 deductible, 25% coinsurance, and a negotiated price of $2,000 per fill.

January. You cover $615 of that first fill yourself. The remaining $1,385 falls into initial coverage at 25%, which is $346.25. Month one costs you $961.25.

February and March. The deductible is finished. 25% of $2,000 is $500 each month. Running total: $961.25 + $500 + $500 = $1,961.25.

April. You need only $138.75 more to reach $2,100. That is all you pay for the April fill instead of the usual $500, and then you are finished.

May through December. Nothing. Eight months of covered prescriptions at no cost to you.

Total out of pocket for the year: $2,100. Without the cap, that same drug would have billed you 25% every month with no ceiling at all — about $6,461 over twelve months. The difference is not a rounding error.

And yes, January still looks brutal — $961 in thirty days is what the next two sections fix.

What Tiers Actually Do to Your Bill

Every Part D plan sorts covered drugs into tiers, and the tier decides what you pay more than the sticker price does. Tiers 1 and 2 hold most generics with the lowest copays, often a few dollars. Tier 3 holds preferred brand names. Tiers 4 and 5 hold non-preferred brands and specialty drugs, frequently billed as a percentage rather than a flat copay. That percentage produces the scary numbers.

Two consequences follow. The same drug can cost very different amounts on two plans, because plans assign different tiers. And a plan may require step therapy or prior authorization on a Tier 4 drug, meaning you try the cheaper option first.

The practical fix is unglamorous: one written page listing every drug you take, the dose, and the tier your plan assigns it. I keep mine taped inside a kitchen cabinet beside a weekly pill organizer I load on Sunday nights. If you prefer paper, a large-print medication log book gives you somewhere to record refill dates and what you actually paid. During Open Enrollment, that one page is the whole job.

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The Medicare Prescription Payment Plan: Smoothing, Not Saving

Let me save you the trouble of misreading this one. The Medicare Prescription Payment Plan does not lower your drug costs or save you a cent. What it does is spread out-of-pocket costs across the calendar year, so you are not writing a $961 check in January.

You stop paying at the counter. Your plan pays the pharmacy and bills you monthly instead. The bill is recalculated every month: what you owe so far, plus last month’s balance, divided by the months remaining in the year. That divisor keeps shrinking, so later bills grow. In a January example Medicare publishes, someone with $80 a month in drug costs pays $80 in January but $241.53 in December — same $960 total, very different shape.

Who it suits: people with high drug costs early in the year. Who it does not: anyone whose costs are low or flat every month, anyone signing up after September, and — this one matters — anyone already getting Extra Help or a Medicare Savings Program. Those cut costs outright, which beats spreading them out.

If Money Is Tight, Check Extra Help Before You Do Anything Else

This is the part I wish more solo agers knew: if your income and savings fall below certain limits, Extra Help — also called the Low-Income Subsidy — pays most of your Part D costs outright.

The 2026 limits: income below $23,940 a year for an individual ($32,460 for a couple), and resources below $18,090 for an individual ($36,100 for a couple). Resources count money in checking, savings, retirement accounts, stocks and bonds. They do not count your home, your car, or up to $1,500 set aside for burial. Alaska and Hawaii have higher income limits.

If you qualify, the 2026 numbers look like this: $0 premium, $0 deductible, up to $5.10 for each generic and up to $12.65 for each brand-name drug, and $0 once your total drug costs reach the $2,100 cap. You also stop owing the Part D late enrollment penalty. You qualify automatically if you have full Medicaid, get help with Part B premiums from a Medicare Savings Program, or receive SSI — otherwise you apply through Social Security. Medicare’s Extra Help page has the details, and my guide to federal and state assistance for low-income seniors living alone lists programs that stack on top of it.

I’ll be blunt — the application is annoying, and it asks for account balances you may have to dig out. Do it anyway. An afternoon of paperwork against $0 premiums is the best hourly rate you will ever earn.

Where these numbers come from

Current for the 2026 plan year. Sources: Medicare.gov on costs in the coverage stages, Medicare.gov Part D cost basics, Medicare costs for 2026, help with drug costs and Extra Help, the Medicare Prescription Payment Plan, and CMS’s final CY 2026 Part D redesign instructions. Figures change each year and vary by plan — confirm current numbers with Medicare.gov or your plan before enrolling.

Some of the links on this page are partner links, and I may earn a commission if you purchase through them — at no extra cost to you. If you want to compare Part D options side by side, start with the Medicare Part D section of my insurance guide.