How Does Child Support Get Calculated?

Every state calculates child support with a guideline formula, and most use one of two models: income shares (the majority) — which combines both parents' incomes, determines what an intact household at that income would spend on the children, and splits that obligation proportionally — or percentage of income, which applies a percentage of the paying parent's income scaled to the number of children. Onto the base amount, formulas add real costs: health insurance premiums for the child, work-related childcare, and often extraordinary medical or educational expenses, allocated between the parents. Parenting time matters in most states: as time approaches equal, the transfer payment shrinks — though it rarely reaches zero when incomes differ.

## What counts as income
More than salary: bonuses, commissions, self-employment earnings, rental income, and recurring distributions typically count. Self-employment is where the disputes live — courts can add back personal expenses run through a business — and when a parent is voluntarily unemployed or underemployed, courts can impute income at earning capacity rather than actual earnings, based on work history and qualifications.

## When courts deviate from the formula
Guidelines are presumptive, not absolute: very high incomes (where formula amounts exceed any child-related need), special-needs children, agreed deviations that still adequately support the child, and other statutory factors can move the number. Judges must generally state reasons for deviating, which keeps the formula as the anchor.

## Modification and enforcement
Support is modifiable when circumstances substantially change — job loss, income jumps, parenting-schedule changes — but only prospectively from the date of filing: arrears that accrued before you filed to modify generally cannot be erased, which is why the universal advice after a job loss is file immediately, not after severance runs out. Enforcement tools are serious: income withholding, tax-refund interception, license suspension, and contempt.

_Informational only; not legal advice._