How is Medicare Advantage developing in Riverside County, California?
Riverside County's MA & other health plan share is 63.0% — above the 51.1% national share by 11.9 points, with 286,854 people in a Medicare Advantage or other health plan out of 455,200 Medicare beneficiaries, on the June 2026 CMS county file. It ranks 2 of 58 California counties by health plan share.
Why trust this number?
- Metric
- MA & other health plan share
- Value
- 63.0%
- Geography
- Riverside, CA (FIPS 06065)
- Period
- June 2026
- Source
- CMS Medicare Monthly Enrollment (BENE_GEO_LVL=County)
- Numerator
- MA_AND_OTH_BENES — beneficiaries in a Medicare Advantage or other health plan (includes cost plans, PACE and demonstrations) — 286,854 here
- Denominator
- TOT_BENES — all Medicare beneficiaries in the county with Part A and/or Part B — 455,200 here
- Formula
- 286,854 ÷ 455,200 × 100 = 63.0%
- Dataset vintage
- June 2026 (prior year June 2025)
- Last refreshed
- 2026-09-26
- Status
- LIVE
Full methodology · Download the source data · CMS dataset
The denominator counts everyone with Part A and/or Part B, including people with Part A only who cannot enroll in Medicare Advantage. Figures published elsewhere on an eligible-only denominator will read higher. Match the basis before comparing.
All figures on this row are from the June 2026 CMS Medicare Monthly Enrollment county file.
Market structure in Riverside County
| MA and other health plan enrollees | 286,854 |
| Total Medicare beneficiaries | 455,200 |
| MA & other health plan share | 63.0% |
| Dual eligibles | 101,609 (22.3% of Medicare) |
| Full-benefit dual eligibles | 100,743 |
| Market type | Switcher (50–65%) |
Every row is from the June 2026 CMS Medicare Monthly Enrollment county file. Carrier counts, the leading carrier and D-SNP share of MA are not shown because this site has no county-level carrier source yet — that needs the CMS CPSC ingest. They previously appeared here from a dataset that has since been withdrawn. Carrier-level enrollment and stars are tracked at the state level.
What changed in the last twelve months
June 2025 file compared with the June 2026 file. Source: CMS Medicare Monthly Enrollment (BENE_GEO_LVL=County).
| Measure | June 2026 | Change | Basis |
|---|---|---|---|
| MA & other health plan enrollment Computed by the pipeline from the two published monthly files. | 286,854 | +2.9% | observed |
| MA & other health plan share A ratio of two published counts, so the change carries both denominators. | 63.0% | -0.1 pp | derived |
| Medicare beneficiaries The county file publishes the current count. It does not publish a prior-year count for this county, and we do not reconstruct one. | 455,200 | not published as a change | observed |
| Dual eligibles Current count from the same file. Same limitation as the line above. | 101,609 (22.3% of Medicare) | not published as a change | observed |
These are observed changes. This panel does not assert why a figure moved: the county file records what happened, not what caused it. A release-over-release view, rather than this twelve-month view, needs the per-vintage metrics store described in docs/backend-architecture.md.
Market Opportunity Score
View score components
| Component | Raw value | Normalized (percentile) | Published weight | Applied weight | Contribution |
|---|---|---|---|---|---|
| Market size | 455,200 beneficiaries | 99.8 | 0.30 | 0.30 | 29.9 |
| Headroom | 37.0% not in MA or other health plans | 14.7 | 0.25 | 0.25 | 3.7 |
| Growth | −0.1 pts | 25.0 | 0.25 | 0.25 | 6.2 |
| Enrollment growth | +2.9% | 61.6 | 0.20 | 0.20 | 12.3 |
| Competition | Not yet available: Market concentration. Needs the CMS Monthly Enrollment by Contract/Plan/State/County (CPSC) file, not yet ingested nationally (loaded for the MA & D-SNP Competitive Lens footprint only). | — | |||
| Carrier diversity | Not yet available: Number of distinct parent organisations competing. Needs the CMS Monthly Enrollment by Contract/Plan/State/County (CPSC) file, not yet ingested nationally (loaded for the MA & D-SNP Competitive Lens footprint only). | — | |||
| Product opportunity | Not yet available: Benefit generosity of plans already sold here. Needs the Landscape and PBP files, not yet ingested nationally (validated for the MA & D-SNP Competitive Lens footprint only). | — | |||
| Quality environment | Not yet available: Star ratings of contracts serving the county. Needs the contract-level Star Ratings files, not yet ingested nationally (contract Overall Star Ratings are loaded for the Competitive Lens footprint only). | — | |||
| Total | Sum of contributions (percentiles shown to 1 decimal) | 52.2 | |||
- Methodology version
- v0.1 · rank-percentile within all US counties, weighted, weights renormalised over available components
- Data vintage
- June 2026 vs June 2025, CMS Medicare Monthly Enrollment (BENE_GEO_LVL=County) (county geography)
- Normalization
- Percentile rank against all 3,199 US counties (ties share the mean rank). Rank-based, so one extreme county cannot flatten the distribution.
- Weighting
- Published weights, renormalised over the components that exist for this county. Components not yet available are listed above, never scored as zero.
- Missing data
- None for this county: every available component is published.
- Limitations
- Not back-tested. No predictive validity, expected enrollment, conversion lift or ROI is claimed. Describes market attractiveness from public CMS counts only; carrier concentration, product and Stars components are not yet included.
Full methodology · Marketing Opportunity Score (MA and D-SNP modes)
So what / Now what Interpretation
Riverside County is a switcher market at 63.0% MA & other health plan share — expansion means winning members from incumbent MA plans on benefits, network and brand.
- Compare to the rest of California on the state page.
- Check 2026 plan exits for orphaned membership contestable in California.
- Sales teams: rank this market on health-plan share headroom and momentum in the county explorer, and see which competitive facts apply on the carrier battlecards.
Neighboring California counties
Provenance — MA & other health plan share, June 2026
- Source file
- CMS Medicare Monthly Enrollment (BENE_GEO_LVL=County)
- Vintage
- June 2026 (prior year June 2025)
- Ingested
- 2026-09-26
- Refresh cadence
- Monthly, following the CMS Medicare Monthly Enrollment release (CCW-derived, roughly three months in arrears)
- Method
- penetration_pct = MA_AND_OTH_BENES / TOT_BENES * 100, rounded to 1 decimal
- Coverage
- All 3199 US counties
- Known limitations
- The denominator includes beneficiaries with Part A only, who cannot enroll in Medicare Advantage. Figures that use an eligible-only denominator will be higher. This file does not carry carrier, plan or star-rating detail. Any such figure needs the CPSC ingest, which is not yet built.