Methodology & Data Sources
Primary Data Sources
All data comes directly from the Centers for Medicare & Medicaid Services (CMS), the federal agency that administers Medicare, Medicaid, and the ACA health insurance marketplaces. CMS publishes comprehensive data on every Medicare Advantage plan offered in the United States, making this the most official source for comparing plan quality, costs, and benefits:
- CMS Medicare Advantage Star Ratings (2026): Quality measures across 10 domains including preventive screenings, chronic disease management, member experience, and customer service. Published annually in October ahead of the Annual Enrollment Period.
- CMS Medicare Advantage Plan Finder Data (2026): Plan premiums, deductibles, plan types (HMO, PPO, PFFS, SNP), county availability, and enrollment figures.
- CMS Supplemental Benefits Data: Coverage for dental, vision, hearing, and other optional benefits offered by each plan contract.
- CMS Quarterly Prescription Drug Plan Formulary, Pharmacy Network, and Pricing Information (SPUF, 2026): Part D prescription drug plan formularies, covered drugs, tiers, and beneficiary cost data, powering our Part D drug and plan lookup pages.
Coverage
Our database covers 2.26 million plan-county records, representing 295 insurance organizations and 3,188 counties across all 50 states and U.S. territories. Each plan contract is matched to every county where it is offered. Separately, our Part D section covers 5,067 prescription drug plans and their formularies for 6,047 drugs.
Processing Pipeline
We download raw plan data files from CMS, including Star Ratings, Plan Finder exports, and supplemental benefits datasets, and join them at the plan contract and county level. Our pipeline:
- Joins plan identifiers (contract ID + plan ID) across CMS files
- Resolves insurer names and organization hierarchies
- Aggregates county-level availability for state and insurer summaries
- Normalizes supplemental benefit flags for dental, vision, hearing, and other categories
No data is modified, interpolated, or editorialized. Missing values are displayed as "N/A" rather than filled with estimates.
Star Ratings Explained
CMS assigns each Medicare Advantage contract an overall star rating from 1 to 5 based on three components: Health inspections (quality measures clinical outcomes), Staffing (customer service and care management), and Member experience (satisfaction surveys). The overall rating is not a simple average, some measures are weighted more heavily by CMS based on their clinical importance. Full methodology is in the CMS Five-Star Technical Users' Guide.
Update Schedule
CMS releases updated Medicare Advantage plan data annually, typically in October/November ahead of the Annual Enrollment Period (October 15 – December 7). We update our database when new CMS plan data becomes available. Current data reflects 2026 plan year. Verify enrollment windows at Medicare.gov and review plan-finder data at HealthCare.gov.
Accuracy Commitment
PlainMedicare reproduces CMS Medicare Advantage data exactly as published. Star ratings, premium amounts, deductibles, plan types, and supplemental benefit indicators are presented without editorial modification or proprietary scoring. No data is modified, interpolated, or editorialized, missing values are displayed as "N/A" rather than filled with estimates. When CMS publishes corrections or updates to plan data, PlainMedicare incorporates the changes in its next database refresh. All plan identifiers (contract ID and plan ID) are preserved to enable verification against the original CMS data sources.
Limitations
- Plan availability, premiums, and benefits change annually during the Medicare Advantage plan year cycle. Always verify current plan details, premiums, and network providers at Medicare.gov or by calling 1-800-MEDICARE before making enrollment decisions.
- Star ratings reflect the most recent CMS measurement period, which typically covers data from the prior calendar year. Ratings may lag actual current plan performance by 12–18 months.
- New plans in their first year of operation may not yet have a star rating assigned by CMS, as the rating methodology requires at least one year of performance data.
- Supplemental benefit availability (dental, vision, hearing) may vary by county within a single plan contract. County-specific benefit details should be confirmed with the plan provider.
- PlainMedicare is not affiliated with CMS, Medicare, or any government agency. This site does not provide insurance advice or enrollment services.