On June 30, 2025, the Centers for Medicare and Medicaid Services (CMS) announced that the accountable care prospective trend (ACPT) in the Medicare Shared Savings Program (MSSP) would be applied to the benchmark trend at a reduced weight of 1/6, a decrease from the original 1/3 weight. While this update will increase performance year (PY) 2024 savings for most accountable care organizations (ACOs) starting an agreement period in 2024, the ACPT will still decrease savings for these ACOs relative to the previous regional/national blended benchmark trend methodology.

Background on the ACPT

The 2023 Medicare Physician Fee Schedule final rule introduced the ACPT¹ with the intent to increase the benchmark trend for ACOs that (a) have a high market share and regional trend weight and (b) have slowed spending growth in their region. In the final rule, CMS noted that they believed the use of the ACPT “would incentivize both greater savings by ACOs and greater program participation.”² Because the 2023–24 ACPT was well below the actual 2023–24 expenditure trend, blending the ACPT with the national/regional benchmark trend generally reduces ACO benchmarks (except in cases where the national/regional benchmark trend is less than the ACPT—this occurs but is not common). With the update of the ACPT from 1/3 weight to 1/6 weight, we estimate that most ACOs will benefit from higher shared savings, but there are still ACOs that will not see shared savings unless CMS removes the ACPT entirely or reduces the weight to zero.

A secondary goal of the ACPT was to increase the predictability of the year-end financial benchmark for MSSP ACOs. However, in 2024, there were several obstacles to that predictability: (a) the ACPT factors were released in late 2024, (b) the ACPT factors were revised in March 2025, and now (c) an updated weight is being applied at settlement.

Estimated PY2024 Impact of the ACPT

Based on Milliman’s ACO Builder®, we have replicated the MSSP methodology on all eligible beneficiaries and providers nationwide. With this, we are able to project PY2024 performance for every MSSP ACO beginning an agreement period in 2024 (“2024 starter”). We projected PY2024 performance for each ACO consistent with its specific participation paremeters (e.g., assignment methodology), except for the minimum savings/loss rate (MSR/MLR), which is not yet publicly available for 2024 starters. (We assumed an MSR/MLR of 0.0% for every ACO for simplicity.) We then performed an estimate of PY2024 settlement performance three times: once with the original 1/3 weight on the ACPT, once with the current 1/6 weight on the ACPT, and lastly with no weight on the ACPT (i.e., as if it did not exist for 2024 starters). The results in Figure 1 show how many ACOs are projected to earn shared savings in each of these scenarios, as well as how many ACOs are expected to lose out on potential shared savings due to the ACPT (i.e., would earn savings under the former two-way benchmark blend, but would earn losses under the three-way ACPT benchmark blend).³

The updated 1/6 ACPT weight is projected to allow five additional ACOs to earn shared savings, and if the ACPT was removed entirely for 2024 starters, then an additional four ACOs are projected to earn shared savings (total of nine more compared to the original 1/3 weight).

In addition, the approximately 120 2024 starters that are projected to earn shared savings are also projected to earn more shared savings in aggregate without the ACPT. Figure 2 shows the average projected savings per ACO and per beneficiary per year (PBPY) for 2024 starters that we estimate will earn shared savings.

Conclusion

For MSSP ACOs beginning an agreement period in 2024, the ACPT in almost all cases will be a headwind to the benchmark. CMS recently updated the ACPT weight from 1/3 to 1/6, which will increase benchmark trends for most ACOs, but even with a weight of 1/6 there are potential ACO savings left on the table due to the difference in estimated trend versus actual experience in 2024. However, we are estimating that 119 out of 140 new-start ACOs (85%) are generating savings at 1/6 ACPT weight, so the majority of ACOs are still expected to perform well in 2024. To understand how the ACPT affects your ACO, please reach out to your Milliman consultant.

¹ For a deeper explanation of the ACPT, see Shellabarger, S., Kuklinski, B., & Champagne, N. (February 3, 2025). Predictability vs. accuracy in MSSP benchmarks [White paper]. Milliman. Retrieved August 11, 2025, from https://www.milliman.com/en/insight/predictability-accuracy-mssp-benchmarks-acpt.

² Medicare and Medicaid Programs; CY 2023 Payment Policies Under the Physician Fee Schedule and Other Changes to Part B Payment and Coverage Policies, 87 Fed. Reg. 69404 (November 18, 2022) (to be codified at 42 C.F.R. pts. 405, 410, 411, 414, 415, 423, 424, 425, & 455). Retrieved August 12, 2025, from https://www.federalregister.gov/documents/2022/11/18/2022-23873/medicare-and-medicaid-programs-cy-2023-payment-policies-under-the-physician-fee-schedule-and-other#p-4114.

³ See section 6 of Centers for Medicare and Medicaid Services. (June 2025). Shared savings and losses, assignment and quality performance standard methodology: Specifications of the accountable care prospective trend (ACPT) and three-way blended benchmark update factor. Retrieved August 11, 2025, from https://www.cms.gov/files/document/medicare-ssp-acpt-specifications.pdf.