Child Support can get tricky if the person paying support has kids with someone else and pays child support for those kids. Child support is based on the net income of the person paying, but net income may be less than it othewise would be if child support is already getting paid out for another family. For example, let's say that the dad is paying support because the kids live with mom. There is 1 child and support is 20%. But he has another child with a different mom who also needs child support. Does he pay the same 20% twice- once to each mom? No. The first mom gets a bigger chunk, taking 20%. The second gets 20% of the net income left after the first mom already got her 20%, which leaves a smaller amount. So- who is the first mom? It is not determined by the first mom to get to the courthouse but rather, the mom who had children with him first. Fair? It depends on how you look at it but regardless, this is the current law on child support in Illinois as determined in a 1998 case called Potts vs. Potts. In case you want to read the case, I will give you the citation (Potts vs. Potts 297 Ill. App 3d 110, 696 N.E. 2nd 1263, 231 Ill. Dec. 692 1998). The court said that prior obligations count as a deduction from net income and thse prior obligations refer to the family that is first in time. But, if the Consumer Credit Protection Act doesn't allow all payments to come out, then percentages get worked out pro-rata. If the child support isn't actually getting paid or there is no court order, then its a different story. If you have a convoluted child support situation based on multiple families, its best to talk to a lawyer who can help you understand it.