How many years can go by for the non-custodial spouse to collect unpaid child support—and what law applies to the unpaid child support? There is a twenty (20) year time limit for the custodial parent to sue the non-paying parent for back child support, but in that length of time the law regarding child support often changes. Does the enforcing court apply the current law for child support--or the law that was in force when the order of support was entered? A recent case from the Colorado Court of Appeals clarified how new laws should apply to the applicable deadlines for such a claim. In this case the mother originally claimed that the child support arrearages totaled $893,285 for the support owed plus interest because the father had stopped paying for child support when the last child turned 18. After proceedings in the lower courts, a judgment of arrears was ultimately entered against the father for $155,000, which was the order reviewed by the Court of Appeals.

The divorce was final in 1983, when the law required support of a child until age 21, but the order of dissolution contained no specific date of termination of the child support obligation. Applying laws that have changed after 1983, the Court ruled that the new laws applied and the father's obligation to pay child support automatically ended when the last child of the marriage turned 19, not 21. The new law effectively modified the old order of child support—reducing the amount of child support in arrears. (Had the mother sought enforcement or modification of the child support arrearages before the law changed in 1991, she may have been able to have the court affirm and preserve the original order for child support until the last child turned 21.) In this case, the Court held that the father was only in arrears for one year of child support, or $4,800.

Although the length of child support was reduced for the non-paying father, the court held that the law provided that interest could be charged on the child support that was owed. The law, which permits compound interest on child support arrearages, is a mandatory law that cannot be "waived," even if the mother delays for many years in pursuing collection of the arrearages (thus driving up the accrued interest). The court noted that the support payment is for the child, not the parent, and thus the custodial parent cannot give up the child's claim for child support.

Even applying the compound interest statute to the amount the father owed of $4,800, from 1995 to the present date, the father will pay a lot less than the $893,285 originally sought by the mother.