What is Minimum Savings Rate (MSR)? Definition, Formula, and Benchmark

The Minimum Savings Rate (MSR) is the percentage below benchmark that an Accountable Care Organization (ACO) must achieve before earning shared savings distribution in the Medicare Shared Savings Program (MSSP) and related CMS ACO models. The MSR establishes a statistical threshold intended to ensure that ACO-reported savings represent genuine cost reduction rather than random variation in the member population's health expenditures. Corresponding Minimum Loss Rates (MLRs) apply in two-sided risk tracks.

MSR values vary by ACO track and attributed population size. Larger ACOs have more statistical stability and can demonstrate genuine savings with smaller margins; smaller ACOs have higher random variation and require larger margins to confidently distinguish savings from noise. For MSSP, MSR ranges from approximately 2.0% for the largest ACOs (80,000+ attributed beneficiaries) to 3.9% for the smallest (5,000 attributed beneficiaries). For some alternative tracks, MSR is a fixed percentage regardless of size.

Operational mechanics: At the end of the performance year, CMS calculates actual ACO spending relative to the ACO's benchmark (historical expenditure baseline adjusted for trends and regional factors). If actual spending is below the benchmark by at least the MSR threshold, the ACO earns shared savings distribution. If actual spending is below benchmark but does not meet the MSR, the ACO earns zero savings despite technically outperforming the benchmark. This "first-dollar" vs. "crossing the MSR" distinction matters substantially for ACO economics.

Example with numbers: An ACO with 25,000 attributed beneficiaries has an MSR of approximately 2.5%. The benchmark is $12,000 PMPY ($300M total for the attributed population). To earn shared savings, actual spending must be below $292.5M (benchmark minus 2.5%). Achieving $294M — a $6M reduction from benchmark — represents 2% savings but does not meet the 2.5% MSR; the ACO earns nothing. Achieving $291M — a $9M reduction — represents 3% savings, exceeds the MSR, and triggers shared savings distribution.

Minimum Loss Rate mechanics in two-sided risk: ACOs in risk-bearing tracks (Track E, ENHANCED in MSSP; Tracks B and C in some models) face shared losses when actual spending exceeds benchmark by at least the MLR threshold. MLR values typically mirror MSR for symmetry. Spending above benchmark but below MLR triggers no loss sharing; spending above MLR triggers loss sharing per the track's percentage.

Shared savings and loss percentage structure depends on ACO track. BASIC tracks (levels A–E) in MSSP use 40–50% sharing rates with increasing loss exposure as levels advance. ENHANCED track allows 75% shared savings but also 40–60% shared losses with caps. Other CMS ACO models (ACO REACH, Primary Care First) use different structures but similar MSR/MLR threshold concepts.

For RCM operations at ACO participant practices, MSR understanding affects financial projection and strategy. ACOs must manage total cost of care with statistical margin — beating benchmark by 1.5% in an ACO with 2.5% MSR yields no shared savings despite genuine cost reduction. Larger ACOs benefit from lower MSR thresholds; small ACOs may strategically merge or affiliate to increase attributed population size and reduce MSR.

Strategic implications include: benchmark quality (accurate baseline adjustment for risk and regional factors is critical), risk score trend management (CMS adjusts benchmarks for population changes), and participation decisions (which track, which model, based on financial tolerance and operational capability).