In deciding whether to implement the ACA's expansion of Medicaid to adults up to 138 percent of FPL, states must assess fiscal effects carefully. States would pay a small percentage of costs for newly eligible adults, beginning in 2017. Enrollment would rise among currently eligible adults, for whom states pay their standard Medicaid share. However, the expansion would increase federal payments for some current Medicaid beneficiaries. With fewer uninsured, states could cut non-Medicaid payments for hospital uncompensated care, mental health services, etc. Federal Medicaid dollars would boost state economies, increasing state revenues. Net gains or losses will vary by state.