Medicare Shared Savings Program

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The Medicare Shared Savings Program (MSSP) is the primary Medicare ACO program. The MSSP was derived from the Physician Group Demonstration Project, which started during the George W. Bush administration, and the MSSP was permanently authorized by the Affordable Care Act. MSSP began in 2012 with two participation options, Track 1 and 2. MSSP Track 3 was added in 2016, and Track 1+ was added in 2018. 

CMS created a new program structure for MSSP in 2019 that the agency calls "Pathways to Success". Tracks 1 and 2 were split to became Basic Levels A through D. Track 1+ became Level E, and Track 3 became the Enhanced Track. Click the image above for NAACOS in-depth analysis of CMS’s final Pathways rule detailing everything ACOs need to know about the program. 

The COVID-19 pandemic has created several changes to MSSP that ACOs should be aware of. Visit our dedicated COVID-19 page for more information on those changes.


NAACOS-Member Resources 

CMS Resources 

News and Advocacy 



  • Accountable Care Organizations Saved Medicare $2.6 Billion in 2019
    • Highlights of ACO results from 2019 and overall savings since 2012
  • NAACOS and 12 other leading organizations support the Value in Health Care Act
  • NAACOS Welcomes CMS's Interim Final Rule Addressing the COVID-19 Pandemic

  • NAACOS Statement on MedPAC’s Position on ACOs During COVID-19

  • Nine Leading Organizations Ask CMS for More Participation Options for ACOs

  • NAACOS Welcomes CMS's Interim Final Rule Addressing the COVID-19 Pandemic

  • More than Half of Participants Likely to Leave Cost-Saving Medicare Program

  • NAACOS Welcomes CMS's Interim Final Rule Addressing the COVID-19 Pandemic

  • NAACOS and nine others ask CMS for relief from COVID-19 response

  • NAACOS Calls on CMS to Address MACRA Implementation Issues

  • NAACOS Urges CMS to Remove Beneficiary Notification Requirement for ACOs

  • CMS announces 2020 Medicare ACO class


  • 2018 performance data from CMS shows MSSP generated $1.7 billion in savings, prompting this NAACOS statement

    • NAACOS resource includes highlights from the 2018 MSSP results

  • CMS Responds to NAACOS Concerns Regarding Beneficiary Notification Requirement

  • CMS proposed 2020 Medicare Physician Fee Schedule makes several changes to MSSP, which is available here along with this CMS factsheet.

  • NAACOS statement on the 2019 Medicare ACO Class

  • NAACOS Statement on MedPAC’s June Report to Congress

  • NAACOS advocacy results in changes to ACO-17 quality measure for 2018

    • NAACOS urges CMS to make changes to scoring of ACO-17 (smoking cessation) quality measure for 2018

  • NAACOS Urges CMS to Postpone Beneficiary Notification Requirement

  • NAACOS advocates for one-sided ACOs to have access to telehealth in revised legislation

  • The application deadline for July 1, 2019 starts was February 19; NAACOS released a statement calling for CMS to extend the deadline into March


  • CMS releases final ACO 'Pathways to Success' rule in December 2018
    • ACOs Saved Medicare $2.7 Billion from 2013-2016
  • Study Shows ACOs Saved Medicare $1.84 Billion from 2013 to 2015

    • 2017 performance data from CMS shows positive results, prompting NAACOS statement

    • NAACOS resource includes highlights of the 2017 MSSP results 
  • NAACOS resource provides highlights of the 2018 Medicare ACO class and shows ACO growth over time

  • NAACOS and five other provider organizations send a letter to CMS requesting that ACOs meeting cost or quality criteria be able to remain in Track 1 
  • NAACOS comments on Extreme and Uncontrollable Circumstances policy for ACOs 
  • NAACOS letter to CMS identifies PY2016 MSSP calculation error affecting ACOs with previous savings and rebased benchmarks in 2016

    • CMS Response about PY2016 Calculations

  • CMS announces 561 MSSP ACOs in 2018

2017 and earlier

  • CMS releases interim final rule establishing extreme and uncontrollable circumstances policies in MSSP for ACOs subject events such as Hurricanes Harvey, Irma, and Maria, and the California wildfires, effective for performance year 2017 
    • CMS releases performance year 2016 MSSP results, available in this Public Use File and CMS Presentation
    • NAACOS letter expresses concerns about delayed PY 2016 results, urges CMS action 
  • NAACOS March 2017 letter to CMS Administrator Seema Verma on ACO improvements 
  • NAACOS policy paper with detailed recommendations for improving the Medicare ACO program

  • CMS Press Release on Announcement of 2017 ACO Class

  • Performance Year 2015 Results

    • Performance Year 2015 CMS Fact Sheet

    • NAACOS Statement on Performance Year 2015 Results and Analysis of 2015 and early program years
  • CMS Releases June 2015 MSSP ACO Final Rule  affecting numerous MSSP policies.

    • CMS summary of the June 2015 Final Rule Provisions for ACOs under the MSSP

    • NAACOS Statement Regarding CMS June 2015 MSSP ACO Final Rule  
  • Performance Year 2013 Results
  • CMS Announces 123 New Accountable Care Organizations