What Is the Income Shares Model?
The most common U.S. child-support model, explained: combined income, the basic-obligation schedule, proportional splitting, and add-ons.
The Income Shares model rests on one idea: a child should receive the same proportion of parental income that they would have received if the family stayed intact. It is used by the large majority of states.
Step 1 — Combine incomes
Both parents’ qualifying income is added. Each state defines “income” slightly differently (gross, net, or adjusted gross), and most subtract things like existing support orders or certain taxes.
Step 2 — Look up the basic obligation
The combined income is matched against the state’s official Schedule of Basic Obligations — a table that says what a family at that income level spends on children. Our calculators use each state’s published schedule where it has been loaded; otherwise they fall back to a reference schedule and are clearly marked as estimates.
Step 3 — Split proportionally
Each parent pays the share of the basic obligation equal to their percentage of combined income. A parent earning 60% of the combined total pays 60% of the basic support.
Step 4 — Add-ons and credits
- Work-related child care and health insurance are usually added and split by income share
- Significant parenting time (often 40%+ overnights) may apply a parenting-time credit
- Extraordinary medical or educational costs may be allocated separately