Monthly Child Support Calculator. This calculator provides an estimate for a single source of income.Our free calculator will help you estimate your Texas child support payments in only a few short minutes. See how parenting time affects the total. The calculator takes the gross income number and applies the formula. Calculation of child support in Texas requires a parent's net income to determine payment amounts. When Texas parents go through a divorce, one parent will often end up with physical custody, or "conservatorship," of any children the couple share. If you work or reside in a state where a state income tax is assessed against your income, enter the monthly amount. Texas offers a monthly child support calculator that can provide you with a basic understanding of what you will likely pay in child support moving forward. How is child support calculated?