When parents have children from multiple partners, the resulting complex families challenge conventions concerning parents’ rights and responsibilities. These challenges are particularly salient for child support policies, which articulate parents’ obligations to their children and determine the amount of support due. Data from Wisconsin suggest that complex families are fairly common and that nonresident fathers’ earnings in these families are typically quite low. The prevalence of these families and their economic vulnerability make expectations about child support particularly important, but family complexity creates tension among key principles underlying the child support system. This study simulates several potential policy regimes, estimating support for hypothetical cases and the actual child support caseload. The findings suggest that different regimes can result in vastly different amounts due and no system is ideal. The most feasible approach may be to set support for each child at a given percentage of a nonresident parent’s income.