The Accountable Care Prospective Trend (ACPT) reduced the benchmark for most accountable care organizations (ACOs) beginning new agreement periods in 2024. The Centers for Medicare and Medicaid Services (CMS) noted that the difference between ACPT expenditure trends and actual 2023 to 2024 expenditure trends “represented an unusually large discrepancy between projected and actual growth rates”1 and elected to reduce the ACPT weight from 1/3 to 1/6 for performance year (PY) 2024.
As of this writing, the ACPT weight remains 1/3 for 2025 and beyond, but large discrepancies between projected and actual growth rates persist. This paper reviews emerging 2025 trends and the expected impact of the ACPT on Medicare Shared Savings Program (MSSP) ACO settlement results.
Background on the ACPT2
The 2023 Medicare Physician Fee Schedule final rule introduced the ACPT 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”.3
However, the actual 2023 to 2024 trend for the aged/disabled (i.e., non-ESRD) population was 9.0%, compared to the 4.9% ACPT trend factor for ACOs starting agreement periods in 2024. For this cohort of ACOs in PY 2025, 4.9% is applied from 2023 to 2024, then further increased by a 4.3% trend from 2024 to 2025, resulting in a cumulative ACPT trend of 9.4% from 2023 to 2025. For ACOs starting agreement periods in 2025, the aged/disabled ACPT trend is 5.1% from 2024 to 2025.
Emerging 2025 trends and what they mean for your ACO
Based on a review of emerging MSSP nationwide expenditure trends through June 2025 and recent seasonality patterns, we estimate that the actual aged/disabled nationwide expenditure trend will be approximately 9.5% from 2024 to 2025. If the ACPT is applied at 1/3 weight in PY 2025, benchmark trends for ACOs beginning agreement periods in 2024 and 2025 will be materially lower than they would have been under the pre-ACPT methodology. For 2024 starters, this compounds with the 2023 to 2024 trend discrepancy, further reducing the benchmark trend. Figure 1 shows the ACPT trend compared to our estimated 2025 expenditure trend, and calculates an “ACPT headwind” that these ACOs will face. The ACPT headwind is calculated as (actual trend × 2/3) + (ACPT trend × 1/3) − (actual trend), and represents the decrease in benchmark trend relative to a trend with no ACPT applied.
As shown in Figure 1, we project that at a 1/3 weight, the ACPT will cause a 1.5% benchmark trend reduction for 2025 starters and a 3.3% reduction for 2024 starters. These reductions are significant in the context of expected ACO savings—in PY 2023 (the last PY before the ACPT), the average MSSP ACO generated savings equal to 4.2% of the benchmark.
Figure 1: ACPT impact for ACOs beginning agreement periods in 2024 and 2025
*Actual trend is estimated based on data through June 2025.
**Benchmark year 3 (BY3) is the last year of the historical benchmark period and is trended forward to the performance year by a blended benchmark trend consisting of 2/3 actual trends and 1/3 ACPT trend under the current ACPT methodology.4
ACPT uncertainty in PY 2025 and PY 2026
Although ACOs cannot directly mitigate the ACPT impact, CMS retains the flexibility to modify the ACPT weight due to “unforeseen circumstances.” CMS has sole discretion to determine whether such circumstances exist in 2025 that warrant a weight adjustment. For PY 2024, CMS announced a weight reduction in June 2025, meaning ACOs may face uncertainty in PY 2025 until the time of the settlement.
Looking further ahead to PY 2026, the ACPT trend factors for 2024 and 2025 appear to be based on the trend assumptions in the CMS Medicare Advantage Rate Announcement.5 In the 2026 Rate Announcement, the projected 2025 to 2026 aged/disabled expenditure trend is 4.3%. Unless actual Medicare expenditure trends slow, ACOs starting agreement periods in 2026 may also face ACPT headwinds. Additionally, ACOs’ continuing agreement periods that began in 2024 or 2025 will continue to experience a headwind unless actual 2025 to 2026 trends are lower than 4.3% by an offsetting amount to the understated trends in 2023 to 2025.
ACPT headwind mitigation
MSSP ACOs subject to the ACPT in 2025 should carefully monitor CMS guidance around the ACPT and account for the ACPT headwind in their settlement accruals. Additionally, ACOs may consider alternative forecasts, with ACPT weights of 1/3, 1/6, and possibly even 0. Lastly, ACOs subject to the ACPT that are not already rebasing into a new agreement period in 2026 (i.e., early renewal) may wish to evaluate rebasing in 2027.6 The cumulative nature of the ACPT means that multiple years of actual trends exceeding the ACPT will lead to a benchmark significantly lower than it would be under the pre-ACPT methodology. Five years of ACPT trends are set at the start of each agreement period, so rebasing will come with a new set of ACPT trends that may result in higher benchmark trends. To understand how the ACPT affects your ACO, please reach out to your Milliman consultant.
1 See https://www.cms.gov/files/document/medicare-ssp-acpt-specifications.pdf.
2 See https://www.milliman.com/en/insight/predictability-accuracy-mssp-benchmarks-acpt for a deeper explanation of the ACPT and https://www.milliman.com/en/insight/2024-acpt-update-shared-savings for an explanation about the reduced ACPT weight in 2024.
3 Federal Register. (2022, November 18). Medicare and Medicaid Programs; CY 2023 Payment Policies Under the Physician Fee Schedule and Other Changes to Part B Payment and Coverage Policies. National Archives, 87 FR 69404 (to be codified at 42 CFR Parts 405, 410, 411, 414, 415, 423, 424, 425, and 455), 4114. Retrieved October 22, 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.
4 See https://www.cms.gov/files/document/medicare-ssp-acpt-specifications.pdf for ACPT methodology and factors.
5 The ACPT factor source documentation reads: “Projections were simulated using archived OACT projection data corresponding to the USPCCs released in the spring of the respective PY1 for each listed agreement period start date. In certain years, adjustments necessitated reliance on internal data archived from Medicare Trustees Reports published the same year.”
6 See a rel="noopener noreferrer" href="https://www.milliman.com/en/insight/mssp-rebasing-considerations-early-renewal" target="_blank">https://www.milliman.com/en/insight/mssp-rebasing-considerations-early-renewal for more information about rebasing in MSSP.