Nationwide, there are three systems of calculating child support payments that each state roughly falls into. The most common system is “income shares.” Thirty-eight states, including Oregon, direct family court judges to use the income shares method. Under that system, child support is calculated by determining how much financial support the children would have received from the non-custodial parent if the parent still lived at home.

The amount of child support is usually determined using financial tables to determine the costs of raising children. The amount of time the children spend with the non-custodial parent is also considered, with various percentages of time used as justification to reduce child support.

There are 10 states that use the “percentage of income” method, which involves directing the non-custodial parent to pay a percentage of his or her income, depending on how many children he or she is supporting. The custodial parent’s income is not directly considered, but the judge generally is allowed to make adjustments based on need. A third method, called the “Melson formula,” combines the income shares system but adds public policy judgments to protect the parents’ basic needs as well as the children’s.

One of the states currently using the percentage of income calculation is Illinois, but the state’s Child Support Advisory Committee is trying to change the law to use income shares instead. It voted 12-3 late in 2010 to recommend the change, and has hired an economist to come up with the financial tables. A bill could go to that state’s Assembly this year.

Not everyone supports the change. One member of the committee who voted against the proposal said she does not believe there would be much change in amount of child support ordered. The proposal would reduce support payments for non-custodial parents who have at least 40 percent of parenting time. Some father’s rights advocates argue that figure is too high.