Child support is a court-ordered payment from the non-custodial parent to the custodial parent to help cover the costs of raising a child. Unlike alimony, which involves significant judicial discretion, child support follows state guidelines that produce relatively predictable outcomes based on income, number of children, and custody split. The sections below break down the two calculation models, the role of custody nights, and the modification rights that apply after a support order is entered.
Income Shares vs Percentage of Income
Roughly 40 states use the Income Shares Model, which assumes a child should receive the same proportion of parental income they would have received if the family remained intact. Both parents' gross (or net, depending on state) incomes are combined, and a basic support obligation is pulled from a state guidelines table. The non-custodial parent then pays their proportional share of that obligation, and any childcare, health insurance, or uninsured medical add-ons are allocated the same way. Approximately 8 states — Texas, Illinois, Wisconsin, Alaska, Mississippi, Nevada, North Dakota, and Arkansas — use the Percentage of Income Model instead. This simpler approach applies a fixed percentage directly to the non-custodial parent's income. Texas, for example, sets support at 20% of net resources for one child, 25% for two, 30% for three, and up to 40% for five or more, with a monthly net-resources cap of $11,700 as of September 2025. The custodial parent's income does not factor into the Texas formula at all. Because the two models produce meaningfully different numbers for the same facts, always confirm which one your state uses before anchoring on a figure.
How Custody Nights Affect the Final Number
Custody time is the single largest factor in child support outside of income, and the mechanics depend on the state's model. Most Income Shares states begin applying a shared-custody credit when the non-custodial parent crosses roughly 40% of overnights — about 146 nights per year — and the credit scales up as the split approaches equal. At a true 50/50 split, several states switch to a cross-credit method where each parent's obligation to the other is calculated separately and the two are netted, with only the difference paid by the higher earner. Percentage-of-Income states generally do not adjust as aggressively for custody time. Texas, for example, applies only a modest adjustment through the "possession order" framework rather than a sliding credit. The practical takeaway: if you are negotiating a parenting plan and moving custody from 25% to 40%, you may see little or no change in the monthly support figure; moving from 40% to 50% can reduce support dramatically. Run multiple scenarios in the Custody Scenarios tab to see the exact break points for your state before agreeing to a schedule.
Modifications, Enforcement, and When Support Ends
Child support orders can be modified when there is a substantial change in circumstances. Most states require a 15–20% change in income or in the calculated support amount before a court will review the order, and many states automatically review active cases every three years on request. Courts also consider changes in custody, significant shifts in the child's financial needs (new medical expenses or specialized education), and major changes in either parent's finances from remarriage, new children, or disability. Enforcement tools are strong: courts can order wage garnishment, suspend driver's and professional licenses, deny passport renewals, intercept tax refunds, and hold non-payers in contempt of court with potential jail time. State child-support enforcement agencies (often called CSEA or Title IV-D offices) handle most cases at no cost to the custodial parent. Support ends at emancipation — typically age 18 or high-school graduation, whichever is later — though New York extends support through age 21 and several states allow or require continued support through college. Children with documented disabilities may receive support into adulthood by separate court order.