The general approach
- We read the state's current guideline statute or court rule, its official schedule or tables, and its official worksheet and instructions, and note the date each took effect.
- We write the state's math in its own file, using the state's own steps, order and rounding where the law or worksheet gives them.
- We test it against the state's worked examples and the edge cases its law names. The tests' expected numbers come from the state's documents, never from our own code.
What the calculators don't decide
Guidelines leave some questions to the court: whether to count income a parent could earn but doesn't (imputed income), whether a deviation from the guideline is justified, and how to treat unusual expenses. Our calculators use the numbers you enter and the guideline's standard steps. Where the law gives the court a choice, the page says so.
Texas
Law: Tex. Fam. Code ch. 154. Net resources are figured the way the Office of the Attorney General's 2026 Tax Charts figure them: Social Security and Medicare (self-employment tax on 92.35% of self-employment income), and one-twelfth of the federal income tax for a single filer with the $16,100 standard deduction. Our formula matches every row of both 2026 charts to within one cent; the tests check all 352 rows and the charts' own worked examples. We then subtract union dues and the children's health and dental insurance or medical and dental support the paying parent is ordered to pay (§154.062(d)), apply the percentage for the number of children (§154.125) or the multiple-family table (§154.129), and cap the net resources the percentage applies to at $11,700 (effective September 1, 2025). Above the cap with other children, we use the §154.128 credit method, since §154.129 applies only up to the cap.
California
Law: Cal. Fam. Code §4055 as operative September 1, 2024. We apply CS = K[HN − (H%)(TN)] with the statute's K table, the time-share factor (1 + H% up to 50%, 2 − H% above), the multipliers for 2 to 10 children, and the low-income adjustment with the Judicial Council's 2026 threshold of $2,929, showing the range and presuming the lowest amount. Add-ons are split under §4061. The tests reproduce the statute's own K example and the Judicial Council's examples in Invitation to Comment SP26-01. For gross income, we estimate 2026 federal and California income tax (FTB's 2026 rates), Social Security, Medicare and SDI for wages only; the official DCSS calculator handles more tax situations.
Florida
Law: Fla. Stat. §61.30 (2026 statutes). The schedule is read from the statute text by a program and checked row by row. We follow Form 12.902(e) line by line, including the substantial time-sharing lines when each parent has at least 73 overnights (20%), and the rule that negative cost-sharing amounts count as zero. The statute doesn't say what to do for an income between two $50 rows; we use the row at or below the income and show the next row's amount.
Illinois
Law: 750 ILCS 5/505 (text in force through December 31, 2026). The HFS Income Shares Schedule and Gross to Net Income Conversion Table (effective March 20, 2026) are read from the HFS PDFs by a program and checked against an independent parse. Standardized net income uses the column for the parent with or without the majority of parenting time. We follow the HFS worksheets, including shared physical care at 146 overnights each, the minimum order and the health insurance premium split. Public Act 104-733 changes the shared care and minimum-order rules on January 1, 2027. The calculator offers both rule sets and switches to the 2027 rules by default on that date; for the 2027 shared care adjustment, until HFS publishes its worksheet, we raise the lower-time parent's amount by the statute's percentage, offset, and cap the payment at the basic worksheet amount.
Indiana
Rules: the Indiana Child Support Rules and Guidelines (effective January 1, 2024) and the Guideline Schedules for Weekly Support Payments, read from the schedule PDF by a program. We follow the Child Support Obligation Worksheet and the Parenting Time Credit Worksheet with each line rounded to the cent and income shares to four decimals, which reproduces the Guidelines' own parenting time example to the cent. The schedule row is the nearest $10 amount (Guideline 3D); a tie at exactly $5 is rounded up, which the Guidelines don't address. Above $9,200 a week we apply the schedule's printed percentage to the combined income.
Gross-pay estimates
Where a calculator offers to estimate net income from gross pay, it uses 2026 federal rules for wages only: the standard deduction, the brackets in IRS Rev. Proc. 2025-32, the child tax credit for the parent filing as head of household, and Social Security and Medicare. The California estimate also includes refundable federal credits, as tax "actually payable" under §4059; the Florida estimate leaves them out, because Florida treats the earned income credit as a reason to deviate, not as income (§61.30(11)(a)8). Real tax situations vary, so enter actual net income when you know it.
Updated November 8, 2026. Each state's section names its sources and effective dates.