All About ACOs

Accountable Care Organizations (ACOs) are groups of doctors, hospitals, and/or other health care providers that voluntarily come together to work collaboratively with the goal of providing better care at lower costs. ACO participants also agree to take on accountability for the total costs and quality of care for their patients. ACOs that reduce the total costs of care for their patient populations can share in the savings with the payer. In certain models, they may also be liable to pay back losses if their costs exceed their spending benchmarks. Before an ACO can share in savings, it must meet quality standards. ACOs are graded based on the quality of care patients receive. If an ACO doesn’t meet the quality standards, shared savings may be reduced, or the ACO may not get any savings at all.

ACOs contract with one or more payers (such as Medicare, Medicaid, or commercial insurers) to take on responsibility for assigned patients. These contracts may vary between payers or specific programs but all ACOs agree to manage both the cost and quality of care for a defined patient population. ACO terminology and program elements can be confusing. This page includes helpful resources, definitions, and answers to frequently asked questions about ACOs.

NAACOS Factsheets

ABCs of ACOs


ACOs & Quality


ACOs & Cost Savings


ACOs & Patients


ACOs & Financial Risk


ACOs & The Future of
Health Care


Other NAACOS Resources

More on Medicare ACOs

The largest ACO model in operation is the Medicare Shared Savings Program (MSSP), which includes 483 ACOs with over 500,000 participating providers serving approximately 11 million Medicare beneficiaries in 2022. (2022 MSSP Fast Facts)

Medicare ACO Program Stats

Medicare ACO Participation by Year

Total MSSP Beneficiaries by Year

New MSSP ACOs by Year


MSSP is a permanent program for traditional Medicare beneficiaries and offers different participation options (tracks) that allow ACOs to assume various levels of risk. Other Medicare ACOs have been/are being operated by the Center for Medicare and Medicaid Innovation (CMS Innovation Center) to test different program design elements. These time bound models include:

*The Global and Professional Direct Contracting Model (GPDC) was redesigned into the ACO REACH Model, as announced by the Centers for Medicare and Medicaid Services (CMS) on February 24, 2022, with policy changes intended to improve the model for beneficiaries and address health equity. The model will continue through its original performance period (2021 – 2026) but will operate under the updated ACO REACH Model name and requirements from January 1, 2023 through December 31, 2026. More information is available from the NAACOS ACO REACH Coalition.

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