According to a report from the Urban Institute, if the 12 non-expansion states were to implement a Medicaid expansion fully in 2023, 3.7 million fewer individuals would be uninsured, a reduction of 29.1%. Groups with the largest gains in coverage due to Medicaid expansion would include non-Hispanic Black persons, young adults, and women, particularly women of reproductive age.
The report can be obtained at https://www.urban.org/sites/default/files/2022-08/3.7%20Million%20People%20Would%20Gain%20Health%20Coverage%20If%20the%20Remaining%20States%20Were%20to%20Expand%20Medicaid.pdf.