---
type: claim
domain: health
description: "UHG and Humana enroll 15.6M beneficiaries (46% market share) with 815 counties showing 75%+ concentration, while beneficiaries average 9+ plan options creating illusion of competition"
confidence: proven
source: "Kaiser Family Foundation, Medicare Advantage in 2025: Enrollment Update and Key Trends (2025)"
created: 2025-07-24
---

# Medicare Advantage market is an oligopoly with UnitedHealthGroup and Humana controlling 46 percent despite nominal plan choice

The Medicare Advantage market exhibits classic oligopoly structure: UnitedHealthGroup (9.9M enrollees, 29%) and Humana (5.7M enrollees, 17%) together control 46% of all MA enrollment. This concentration exists despite beneficiaries having an average of 9 plan options, with 36% of beneficiaries having 10+ options. The nominal choice masks structural market power.

Geographic concentration is even more extreme: 815 counties (26% of all counties) have 75%+ enrollment concentration in UHG and Humana combined. This means in more than a quarter of US counties, three out of four MA beneficiaries are enrolled with one of two parent organizations.

The market is consolidating further, not diversifying. In 2025, Humana lost 297K members while UHG gained 505K, suggesting the dominant player is absorbing share from the #2 player. The top 5 organizations (UHG, Humana, CVS/Aetna, Elevance, Kaiser) control 70% of enrollment, leaving only 30% for "all others."

## Evidence

**Market share by parent organization (2025):**
- UnitedHealth Group: 9.9M (29%)
- Humana: 5.7M (17%)
- CVS Health (Aetna): 4.1M (12%)
- Elevance Health: 2.2M (7%)
- Kaiser Foundation: 2.0M (6%)
- All others: 10.3M (30%)

**UHG + Humana = 15.6M enrollees (46% of market)**

**Geographic concentration:**
- 815 counties (26% of all counties) have 75%+ enrollment in UHG + Humana
- This represents structural market power at the local level where beneficiaries actually choose plans

**2024-2025 enrollment changes:**
- UHG: +505K members
- Humana: -297K members
- Net effect: market leader gaining share from #2 player

**Nominal choice metrics:**
- Average parent organization options per beneficiary: 9
- 36% of beneficiaries have 10+ plan options
- Yet 46% of enrollment concentrates in two organizations

The disconnect between plan choice (9+ options) and enrollment concentration (46% in two companies) indicates that nominal choice does not produce competitive market dynamics. Beneficiaries may have many options, but they systematically select from a duopoly.

---

Relevant Notes:
- Devoted is the fastest-growing MA plan at 121 percent growth because purpose-built technology outperforms acquisition-based vertical integration during CMS tightening.md
- Kaiser Permanentes 80-year tripartite structure is the strongest precedent for purpose-built payvidor exemptions because any structural separation bill that captures Kaiser faces 12.5 million members and Californias entire healthcare infrastructure.md
- the healthcare attractor state is a prevention-first system where aligned payment continuous monitoring and AI-augmented care delivery create a flywheel that profits from health rather than sickness.md

Topics:
- domains/health/_map
