Income Shares vs. Percentage of Income Models
The two dominant child-support calculation models are income shares and percentage of obligor income. Income shares (used by most states) pools the parents' income and allocates a percentages of that pool to the obligor parent in proportion to their income share. For example, if the obligor earns 60% of the total income, they pay 60% of the child-support obligation for that income level. The obligation amount is determined by a statutory table, which varies by number of children (more children, higher percentage obligation). Percentage of obligor income, used by some states and historically more common, sets support as a fixed percentage of the obligor's gross income: 17% for one child, 25% for two, and so on. The income-shares model aims for fairness by recognizing both parents' economic contributions; the percentage model is simpler and more predictable.
Adjustments and Deviations
Base formulas assume a presumptive income level (often $160,000 or higher is capped). Income above that cap can be adjusted upward or left out, depending on state discretion. Deviation factors allow courts to depart from the formula: shared custody (reducing obligor's support because the obligor has the child part-time), special needs, private school, other children the obligor supports. The obligor's income usually means gross income (before taxes and deductions), though some states allow deductions for existing court-ordered support. Support orders are modifiable if there is a substantial change in circumstances (job loss, new child, custody change), and enforcement is aggressive: wage garnishment, license suspension, contempt proceedings.