How child support is calculated in your state
Child support calculations in the United States follow one of three models depending on your state. Understanding which model applies is the first step to estimating your obligation or entitlement.
The income shares model — used by 41 states — assumes children should receive the same proportion of parental income they would have received if the family stayed intact. Both parents' incomes are combined, a guideline obligation is determined from a state schedule, and each parent's share is calculated proportional to their income. The non-custodial parent typically pays their share to the custodial parent, with adjustments for parenting time and add-on expenses.
The percentage of income model, used in Alaska, Mississippi, Nevada, North Dakota, Texas, and Wisconsin, applies a percentage to the non-custodial parent's income only. The percentage scales with the number of children. Alaska, Texas, and North Dakota apply it to net income; the other states use gross or adjusted gross income.
The Melson Formula — used in Delaware, Hawaii, and Montana — is the most complex. It first reserves a self-support amount for each parent, then determines a primary support need for the children, then allocates remaining income proportionally. Because of its complexity, estimates from any calculator should be confirmed against the state's official worksheet.
The income shares model (41 states)
In income shares states, the court looks at both parents' combined gross monthly income and consults a state-published Schedule of Basic Child Support Obligations. This schedule produces a baseline dollar figure representing the cost of raising the children at that income level. Each parent is then responsible for a percentage of that obligation equal to their share of combined income.
Add-ons — health insurance premiums for the children, work-related childcare, and sometimes extraordinary medical expenses — are added on top of the base obligation and split proportionally. Parenting time credits reduce the non-custodial parent's obligation as their parenting time approaches 50%.
The percentage of income model (6 states)
In percentage states, only the non-custodial parent's income matters for the base calculation. A flat percentage is applied based on the number of children. For example, Alaska applies 20% for one child and 27% for two children to the obligor's adjusted net income under Civil Rule 90.3. Texas applies 20% for one child and 25% for two children to net resources, capped at 40%. Illinois moved from this model to income shares in July 2017.