Hana Health
All posts
Insights
Hana Health
Value Based CareOctober 15, 2026

Medicare Star Ratings Adherence Measures Explained

Matteo

Updated October 2026. Written by Matteo Grassi, cofounder of HANA Health, trained in psychology.

The Medicare Star Ratings medication adherence measures are three Part D scores that show how many plan members with diabetes, high blood pressure or high cholesterol fill their prescriptions often enough to cover at least 80% of their treatment days. CMS counts each measure three times in the 2027 ratings, and Medicare Advantage drug plans averaged about 89% on all three.

As a psychologist, I'd add that a late refill is often the first visible sign that a patient has quietly stepped away from a treatment.

Key facts

What are the Medicare Star Ratings medication adherence measures?

They're three Part D quality measures that look at refill behavior. One covers diabetes medications, one covers blood pressure medications in the RAS antagonist family (ACE inhibitors, ARBs and direct renin inhibitors), and one covers statins for cholesterol.

CMS adapted all three from measures developed by the Pharmacy Quality Alliance, a nonprofit that maintains pharmacy quality standards. The Medicare diabetes measure covers several drug classes, including biguanides such as metformin, sulfonylureas, thiazolidinediones, DPP-4 inhibitors, GIP/GLP-1 receptor agonists, meglitinides and SGLT2 inhibitors. You can read the full list in the Pharmacy Quality Alliance measure overview.

The measures don't ask whether a patient's blood pressure or blood sugar is controlled. They ask whether the patient picked up enough medication. That's why CMS classes them as intermediate outcome measures, one step before a clinical result.

How does CMS calculate medication adherence?

CMS uses proportion of days covered, or PDC. PDC is the share of days in a patient's treatment period that are covered by a prescription fill for the same drug or another drug in its class.

The treatment period starts on the patient's first fill of the year and ends at the earliest of the last day of enrollment, death, or December 31. Here are the rules that decide who is counted:

  • Fills: the patient needs at least two fills on different dates of service.
  • Length: the treatment period must be at least 91 days.
  • Enrollment: the patient must stay enrolled in the same Part D contract with no gaps.
  • Pass mark: a PDC of 80% or higher puts the patient in the numerator.
  • Size: contracts with 29 or fewer eligible patients aren't rated.

Some patients are left out completely. Members in hospice and members with end stage renal disease or dialysis coverage are excluded. In the diabetes measure, anyone with one or more insulin prescriptions in the treatment period is excluded too. All of this comes from the CMS 2027 Technical Notes.

Why do the adherence measures count so much in the Star Ratings?

Each one has a weight of 3 because CMS weights measures by type. The 2027 methodology gives the highest weight to improvement measures, then to outcome and intermediate outcome measures, then to patient experience and access measures, and the lowest weight to process measures.

A weight of 3 counts three times as much as a weight of 1. CMS multiplies each measure's star rating by its weight, adds the results, and divides by the total weight of the measures the contract was rated on. Because three of the Part D measures sit at weight 3, adherence moves the summary rating more than most clinical process measures do.

The cut points are tight. For Medicare Advantage drug plan contracts in 2027, the diabetes measure needs 91% for four stars and 93% for five. The blood pressure and statin measures need 90% for four stars and 93% for five. The national average for each of the three was 89%. A plan sitting at the average is about one or two points from four stars.

How much money is tied to Star Ratings?

Quite a lot, though it flows to plans first. Plans that reach four stars or more get a higher payment benchmark. KFF reports that most plans in bonus status get a five percentage point increase in their benchmark.

The scale is large. KFF estimates the bonus program at no less than $13.4 billion in 2026, with 68% of Medicare Advantage enrollees (nearly 24 million people) in plans that qualify. In the 2027 ratings, CMS says about 37% of Medicare Advantage drug plan contracts (188 contracts) earned four stars or more, and about 71% of enrollees are in those contracts.

None of that money is paid to your practice because of these measures. Some plans share quality incentives with practices through their contracts, and the terms vary by plan. If you're in a Medicare Advantage network, read what yours says.

What does 80% adherence look like in refill terms?

It's more forgiving than people expect, and also less forgiving. Here's an illustration with simple numbers. It isn't a CMS example, and the real calculation also adjusts for overlapping fills.

  1. A patient starts a statin and the treatment period runs 300 days.
  2. The pass mark is 80% of 300 days, which is 240 days covered.
  3. Ten on time 30 day fills cover 300 days, so the PDC is 100%.
  4. Missing two fills leaves 8 fills times 30 days, which is 240 days covered. The PDC is 80% and the patient passes.
  5. Missing three fills leaves 7 fills times 30 days, which is 210 days covered. The PDC is 70% and the patient fails.

The gap between pass and fail is one missed refill. Now remember the plan average is 89%. A contract with a thousand eligible patients needs about 910 of them above the line to earn four stars on the diabetes measure. Every late refill matters at the margin.

What this means for your practice

You don't get a Star Rating, but you may be able to influence it. Patients decide whether to fill, and a practice is often the first place a problem shows up: a side effect, a cost surprise, confusion after a dose change.

Here are practical steps to consider, none of which come from CMS evidence that a single tactic moves the measure:

  • Ask at visits whether patients are picking up all three drug types, and note the reason when they aren't.
  • Treat a missed refill as a clinical signal, not only a pharmacy one.
  • Review statin intolerance and cost barriers before a patient quits.
  • Check what your Medicare Advantage contracts say about quality incentives, and which measures they name.

If you're in an ACO, these measures sit beside the ones in our ACO quality measures guide. The accountable care model that starts in 2027 is covered in our LEAD model explainer.

HANA helps practices reach patients by phone between visits, so a refill problem can be raised before it becomes a gap. You can see how it works on the care coordination page.

Frequently asked questions

Does my practice get its own Star Rating?

No. CMS rates Medicare Advantage and Part D plan contracts. Your patients' fills count toward the contract they're enrolled in, so the score is shared across every practice in that plan's network.

Which patients are left out of the adherence measures?

Members in hospice, members with end stage renal disease or dialysis coverage, and (for the diabetes measure only) anyone with an insulin prescription in the treatment period. A patient also needs two fills and a treatment period of at least 91 days to be counted.

When do the 2027 Star Ratings affect plan payments?

CMS published them on October 8, 2026, and they affect 2028 quality bonus payments. Open enrollment runs from October 15 to December 7, 2026, and the ratings appear on Medicare Plan Finder during that window.

Are the adherence measures based on my records or on pharmacy claims?

Pharmacy claims. The 2027 ratings use Prescription Drug Event data with dates of service in 2025. Your chart doesn't feed the score, so what a patient says at a visit won't change it.

What does a five star adherence score require?

For Medicare Advantage drug plan contracts in 2027, 93% of eligible members need a PDC of 80% or higher on each measure. Cut points are recalculated every year, so next year's thresholds can differ.

Sources

  1. Centers for Medicare and Medicaid Services, 2027 Star Ratings Measures and Weights, 2026. https://www.cms.gov/files/document/2027-star-ratings-measures.pdf
  2. Centers for Medicare and Medicaid Services, Medicare 2027 Part C and D Star Ratings Technical Notes, September 30, 2026. https://www.cms.gov/files/document/2027-tech-notes-2026-09-30.pdf
  3. Centers for Medicare and Medicaid Services, 2027 Medicare Advantage and Part D Star Ratings fact sheet, October 8, 2026. https://www.cms.gov/newsroom/fact-sheets/2027-medicare-advantage-part-d-star-ratings
  4. KFF, Medicare Will Spend More Than $13 Billion on the Medicare Advantage Quality Bonus Program in 2026, updated August 12, 2026. https://www.kff.org/medicare/medicare-will-spend-more-than-13-billion-on-the-medicare-advantage-quality-bonus-program-in-2026/
  5. Pharmacy Quality Alliance, Measure Implementation, 2026. https://www.pqa.org/measures/measure-implementation/

This article is educational and isn't billing, coding, clinical or legal advice. Check current CMS guidance and your MAC before you bill. If you want to talk through how outreach could fit your practice, book a discovery call with Matteo.