Tool · 2026 · Live
Coparent Math
A child support calculator for Texas, New York and Virginia that shows its working. Every step of the state's formula, with the arithmetic and the section of law behind it.
Coparent Math
A child support calculator for Texas, New York and Virginia that shows its working. Every step of the state's formula, with the arithmetic and the section of law behind it.
What it is
A child support calculator and a set of guides for three US states, each with a different model. Texas takes a percentage of the paying parent’s net resources. New York takes a percentage of both parents’ combined income, up to a cap. Virginia uses income shares: the combined income sets the children’s need from a schedule, and each parent pays their part of it.
You describe the family in one sentence: the children, both incomes, the days with each parent, child care. You get the guideline amount, who pays it, and every step of the formula written out as arithmetic, each step with the statute section it comes from.
The site never says mother, father or custodial parent. It says “the parent the children live with” and “the other parent”, and draws both in the same colour.
How it works
Each state’s guideline is a list of steps in a rule file, with dated values for the figures that change on their own calendar: New York’s income cap, Texas’s cap on net resources, the poverty guideline. Virginia’s 844-row schedule is imported straight from the statute.
Texas works from net income, so the engine includes a federal tax and payroll module. Its results match 340 of the 342 rows of the Texas Attorney General’s tax charts to the cent.
The same engine runs in the browser for the calculator and at build time for every figure in the guides. The guides can’t contain a typed dollar amount or percentage: the build rejects them.
What checking the law found
Before launch, every rule was compared with the statutes, and that caught errors in my first version:
- In Texas, health insurance paid by the parent the children live with was ignored. The law adds it, up to a cap.
- In Virginia, child care paid directly by the other parent was counted twice. One test family went from $1,230.60 a month to $430.60.
- New York’s low-income tiers added child care and health costs automatically. The statute leaves those to the court.
Where the statute is silent, the source is named. New York’s rule for exactly equal parenting time comes from appellate cases, read in the official reports. Anything that still can’t be confirmed is flagged on the result.
Try it
Work out a guideline amount. It’s free and keeps nothing you type. The guides go through the situations that change the amount, from shared custody to back child support. It’s an estimate of the guideline, not legal advice: a court can order a different amount.