HMO Market Share and Enrollment Trends

HMO plans occupy a significant and measurable portion of the US health insurance market, influencing how tens of millions of Americans access medical care. This page examines how HMO enrollment is tracked, what forces drive fluctuations in market share, and how HMO penetration compares across plan types and market segments. Understanding these trends matters for employers designing benefit packages, policymakers evaluating managed care's reach, and consumers weighing plan options.

Definition and scope

HMO market share refers to the proportion of health insurance enrollees covered under a Health Maintenance Organization structure relative to all plan types — including PPOs, EPOs, POS plans, and HDHPs. Enrollment data is tracked across three primary markets: employer-sponsored insurance (ESI), the individual and small-group markets (including ACA Marketplace plans), and public programs such as Medicare Advantage and Medicaid managed care.

The Kaiser Family Foundation (KFF) is the primary public source for employer-sponsored market share data. According to KFF's Employer Health Benefits Survey 2023, HMO plans covered 13% of covered workers enrolled in employer-sponsored insurance in 2023, compared to PPO plans at 47%. This represents a long-term contraction from HMO dominance in the 1990s, when HMOs briefly captured more than 30% of the ESI market.

In the Medicare Advantage segment, HMO-type structures — including local HMOs and HMO-POS hybrids — represent the largest single plan type. The Centers for Medicare & Medicaid Services (CMS) reported that as of 2023, approximately 67% of Medicare Advantage enrollees were in HMO or HMO-POS contracts, accounting for roughly 19 million beneficiaries (CMS Medicare Advantage Enrollment Data, 2023).

Medicaid managed care tells a parallel story. The Medicaid and CHIP Payment and Access Commission (MACPAC) has documented that risk-based managed care — predominantly HMO-structured contracts — enrolled approximately 72% of all Medicaid beneficiaries in 2022, reflecting states' sustained preference for capitated HMO arrangements to manage Medicaid costs.

How it works

Market share is calculated by dividing the number of enrollees in HMO-type plans by total enrollees across all plan types within a defined market segment, then expressing the result as a percentage. Because the ESI, Marketplace, Medicare Advantage, and Medicaid segments are measured by separate agencies using distinct methodologies, aggregate national HMO enrollment figures require combining data from KFF, CMS, and MACPAC rather than citing a single unified source.

Enrollment trends are driven by four primary variables:

  1. Premium differentials — HMO premiums are structurally lower than PPO premiums in most markets due to tighter networks and capitated provider payment. KFF's 2023 survey found the average annual premium for employer-sponsored single coverage was $8,435 for all plan types combined; HMO products typically run below that average.
  2. Network adequacy regulations — State and federal network adequacy rules under the ACA affect how restrictive HMO networks can be, directly influencing plan attractiveness. More on the regulatory framework appears at State Regulation of HMO Plans.
  3. Medicare Advantage growth — Total Medicare Advantage enrollment grew from roughly 13 million in 2010 to over 30 million by 2023 (CMS Fast Facts), pulling HMO enrollment upward even as the ESI HMO share declined.
  4. Medicaid expansion — Post-ACA Medicaid expansion added millions of enrollees into managed care contracts structured as HMOs, amplifying the segment's enrollment base.

Common scenarios

The gap between HMO market share in ESI versus government programs illustrates two distinct enrollment dynamics. In the employer market, workers with income and plan choice authority have migrated toward PPOs and HDHPs for broader network access, causing HMO share to compress steadily since 2000. The pattern is visible in KFF longitudinal survey data stretching back to 1996.

In contrast, Medicare Advantage and Medicaid managed care have expanded HMO-structured enrollment substantially. Beneficiaries in these programs often face constrained plan choices, lower cost-sharing under HMO options, and geographic markets where HMOs dominate insurer offerings. Readers evaluating specific insurers can consult Largest HMO Providers by State for a market-by-market breakdown.

A third scenario involves the ACA individual Marketplace, where HMO and EPO designs together represent a majority of available products in many rating areas. The differences between these structures are covered at HMO vs EPO: What Sets Them Apart.

Decision boundaries

For employers and benefits administrators, the relevant threshold question is whether HMO cost savings justify the employee satisfaction tradeoffs that come with network restrictions and referral requirements. KFF's 2023 survey shows PPO plans still dominate employer offerings because plan sponsors in large-employer segments face workforce pressure to provide flexible access — a structural tension examined further at Managing Employee Satisfaction with HMO Restrictions.

For policymakers, HMO enrollment concentration in Medicare Advantage and Medicaid creates systemic questions about network adequacy, access in rural areas, and the sustainability of capitation rates. The hmoauthority.com resource index provides a structured entry point for exploring how these regulatory and structural factors interact.

For individual enrollees, HMO plans are most favorable when the enrollee's primary care provider, specialist network, and geographic location align with the plan's network boundaries. The referral and gatekeeper model — described in detail at How HMO Referrals Work — is the primary operational distinction that differentiates HMO enrollment experience from PPO or EPO coverage.

References

The law belongs to the people. Georgia v. Public.Resource.Org, 590 U.S. (2020)