SB 1811, prohibits health maintenance organizations (HMOs) and insurers from using extrapolation—a mathematical technique to estimate results for larger batches of claims not reviewed—during audits of physicians, providers, or preferred providers. The bill stipulates that any additional payment owed to a provider or refund due to the HMO or insurer must be calculated based on actual overpayments or underpayments identified in the audit, not through extrapolated estimates. The prohibition applies to contracts entered into or renewed on or after September 1, 2025. However, specific provisions, such as those excluding certain governmental health benefit plans like Medicaid and CHIP from applicability, remain unchanged. This measure aims to ensure fairness and accuracy in claim audits, protecting providers from potentially inflated repayment demands derived from generalized calculations.