The growth in divorce and non-marital fertility in the United States has spurred complex family structures formed as a result of multipartner fertility, where parents who share at least one child together also have children with other partners. This study examines how multipartner fertility among men and women affect non-resident fathers' child support contributions, measured by payments towards and compliance with court-mandated child support orders. The study utilizes longitudinal data from the Fragile Families and Child Wellbeing Study (N=2,612) to show that child support contributions are significantly lowered by female multipartner childbearing once omitted variable bias is addressed.