Three Formulas, One Country: How US Child Support Calculations Diverge by State

Findings

Income Shares dominates at 42 of 51 jurisdictions

PlainChildSupport's states table lists 42 jurisdictions with formula_type column set to Income Shares, covering 50 states plus DC. Each row stores base percentages, income cap values, and URLs to official state calculators. Income Shares model combines both parents' incomes, then pulls obligation amounts from state-specific schedule tables. National Conference of State Legislatures — Child Support Guidelines by State Developers access these via joins on state_fips in child support calculators. DC row shows median household income at $90,842 with income cap above that level. Maryland row records $90,203 median household income, also Income Shares with cap exceeding median. New Jersey row lists $90,703 median household income under same formula_type. US Census Bureau — ACS 2022, Table B19013 (Median Household Income)

Low-median-income states apply Income Shares alongside self-support floors in states table. West Virginia row holds $48,037 median household income. Arkansas row shows $48,952 median household income. States table formula_type column confirms Income Shares for both. US Census Bureau — ACS 2022, Table B19013 (Median Household Income) Ten jurisdictions deliver verified official calculators replicated in PlainChildSupport: California, Florida, Georgia, Michigan, New York, North Carolina, Ohio, Pennsylvania, plus Illinois and Texas from other models. All 10 embed parenting-time adjustment at 40% overnights, or 146 nights per year. Formulas-explained guide details Income Shares schedule lookups.

Enforcement data ties to Income Shares states. Iowa collects 68.4% of assessed support. North Dakota reaches 67.5% collections. Minnesota hits 67.2% in FY2023 data. Office of Child Support Enforcement — FY2023 Preliminary Report States table links to enforcement agency calculators for these jurisdictions. High collection rates pair with Income Shares formula_type in 42 rows. West Virginia self-support floor compresses obligations at $48,037 median household income level.

Percentage of Income: Illinois and Texas both at 20%, but the math differs

States table marks 6 jurisdictions with formula_type as Percentage of Income: Illinois at 20%, Texas at 20%, Nevada at 18%, Wisconsin at 17%, North Dakota at 14.35%, Mississippi at 14%. National Conference of State Legislatures — Child Support Guidelines by State Base percentages column stores these rates for one child. Spread between lowest Mississippi 14% and highest Illinois or Texas at the matching one-fifth-of-income rate spans 6 percentage points. Non-custodial income alone drives obligations, unlike Income Shares combined totals. Illinois state page replicates official calculator at the same flat rate.

Illinois and Texas rows share identical base percentages yet diverge from Income Shares math. Texas Percentage of Income applies the flat one-fifth rate to non-custodial gross income. Texas state page holds verified calculator matching state enforcement tool. Both appear in 10 verified jurisdictions list. North Dakota row lists 14.35% base with 67.5% collections rate. Mississippi row shows 14% base percentages and 49.3% collections. Office of Child Support Enforcement — FY2023 Preliminary Report States table income cap column varies across these 6 rows.

Parenting-time adjustments activate at 40% overnights in verified Percentage states. Illinois calculator triggers offset at 146 nights per year. Texas version follows same 40% threshold. Nevada 18% base rate row links to state agency guidelines. Wisconsin 17% stores in base percentages column without verified calculator. Six rows total under this formula_type enable direct rate comparisons. State child support enforcement agencies — official calculator URLs

Melson's 3 holdouts — Delaware, Hawaii, and Montana

Three jurisdictions claim formula_type Melson in states table: Delaware, Hawaii, Montana. National Conference of State Legislatures — Child Support Guidelines by State Melson subtracts self-support reserve from each parent's income before percentage application. Delaware row links to official guidelines via states table URL column. Delaware state page documents reserve test. Hawaii row records Melson parameters in base percentages column. Montana completes the 3 rows with same formula_type.

States table self-support reserve values appear in Melson rows for Delaware, Hawaii, Montana. No Melson states join 10 verified calculators group. Delaware Melson applies after reserve subtraction, differing from Percentage flat rates. Hawaii guidelines URL points to enforcement agency tool. Montana row holds income cap alongside Melson details. State child support enforcement agencies — official calculator URLs Total Melson count stays at 3 across 51 jurisdictions.

Enforcement collections provide context for Melson states. Mississippi 49.3% rate contrasts North Dakota 67.5%, though different formula_type. Delaware self-support reserve aligns with low-income compression patterns like West Virginia $48,037 median. Hawaii and Montana rows enable Melson-specific queries via formula_type filter. Office of Child Support Enforcement — FY2023 Preliminary Report States table page lists all 51 with Melson isolated.

States table captures formula_type distribution across 51 jurisdictions: 42 Income Shares rows, 6 Percentage of Income rows with 14% to 20% base rates spanning 6 points, 3 Melson rows. High-income DC $90,842, Maryland $90,203, New Jersey $89,703 use Income Shares caps above medians; low-income West Virginia $48,037, Arkansas $48,952 compress via floors. Verified calculators in 10 states embed 40% overnights threshold, including Illinois and Texas at the shared one-fifth base. Collections range from Iowa 68.4% to Mississippi 49.3%. US Census Bureau — ACS 2022, Table B19013; Office of Child Support Enforcement — FY2023 Preliminary Report

Comparative jurisdictional notes

Comparing IV-D child-support administration across the 51 jurisdictions reveals administrative patterns that defy simple aggregation. Income-Shares states like Iowa, North Dakota, and Minnesota deliver collection-efficiency ratios above 67% by leveraging integrated state-disbursement-unit (SDU) ledger reconciliation, employer-direct income-withholding-order (IWO) routing under OMB-0970-0154 standardized templates, and aggressive licensure-suspension referrals through driver-license-suspension and professional-license-revocation administrative pathways. Percentage-of-Income states such as Texas, Illinois, and Wisconsin emphasize lump-sum-payment intercept reporting through new-hire-directory clearinghouses and Federal-Parent-Locator-Service (FPLS) cross-jurisdictional asset-trace queries. Melson-formula jurisdictions Delaware, Hawaii, and Montana incorporate self-support-reserve subtraction before percentage application, producing materially lower obligations at low-income brackets while preserving guideline-presumption integrity at higher earnings. Tribal-court IV-D coordination adds another layer in Alaska, South Dakota, North Dakota, and New Mexico where Bureau-of-Indian-Affairs comity considerations interact with state-court continuing-exclusive-jurisdiction (CEJ) doctrine under the Uniform-Interstate-Family-Support-Act (UIFSA) framework. Cooperation-with-paternity-establishment is a TANF eligibility precondition under Title IV-A, creating direct programmatic linkage between cash-assistance enrollment and child-support-establishment caseload growth. Bradley-Amendment-1986 prohibits retroactive modification of arrears, while Personal-Responsibility-and-Work-Opportunity-Reconciliation-Act-1996 (PRWORA) standardized state new-hire reporting, in-hospital-paternity acknowledgment programs, and license-suspension authority. State-court-rule-of-civil-procedure variation governs contempt-enforcement procedures, with civil-contempt confinement bounded by Turner-v-Rogers-560-US-431 due-process requirements and criminal-contempt subject to jury-trial threshold doctrine.

Family-services reference notes

Modern child-support administration draws on Title IV-D of the Social Security Act (42 USC 651-669b), the Office of Child Support Enforcement (OCSE) within the Administration for Children and Families (ACF), and a federal-state cooperative-agreement structure that channels federal-financial-participation (FFP) reimbursement at varying match rates. Paternity-establishment proceeds through voluntary acknowledgment under the in-hospital paternity-affidavit pathway, judicial adjudication, or administrative determination via genetic-testing under 45 CFR 303.5 with chain-of-custody buccal-swab DNA-collection protocols. Income-withholding implements through OMB-Form-0970-0154 standardized Income-Withholding-Order (IWO) employer service, with lump-sum-payment reporting requirements covering bonuses, severance, and stock-vesting events. The National-Medical-Support-Notice (NMSN) directs employers to enroll dependents in employer-sponsored group health insurance under ERISA-preemption-exemption provisions. Tax-intercept enforcement uses the Federal-Tax-Refund-Offset-Program coordinated through the Treasury-Offset-Program (TOP) and Department-of-Treasury Bureau of the Fiscal Service, with state-tax-refund offsets layered separately under Franchise-Tax-Board or Department-of-Revenue cooperative agreements. Passport-denial under 22 USC 2714a triggers when arrears exceed $2,500. License-suspension authority spans driver-license, professional-license, recreational-license, and business-license categories under PRWORA-1996 mandatory-state-law provisions. Interstate-case processing under UIFSA codifies long-arm jurisdiction, registration of foreign orders, continuing-exclusive-jurisdiction (CEJ) preservation, and direct income-withholding without intervening state-court action. The Hague-Convention-on-the-International-Recovery-of-Child-Support extends UIFSA principles to 40+ treaty countries with central-authority case-coordination protocols. The Income-Withholding-for-Support-Act (ICSA) federalized employer-compliance penalties. State-law guideline-models include Income-Shares (parental-income combined with schedule-table lookup), Percentage-of-Obligor-Income (flat or graduated rate against non-custodial-parent gross or net), and Melson formula (three-step self-support-reserve / primary-need / standard-of-living-adjustment SOLA stages). Self-support-reserve provisions under low-income-adjustment subtables reduce obligations when obligor income falls below subsistence thresholds. Modification standards apply substantial-change-in-circumstances doctrine, with PRWORA mandating three-year automatic-review opportunities. Arrears compute with statutory-interest-rate (typically 6%-12% APR depending on jurisdiction), retroactive-support computed back to filing date, and prospective-support starting at the order date. Title IV-A TANF cooperation-requirements link cash-assistance enrollment to child-support-establishment caseload growth, while Title IV-E foster-care reimbursement intersects with paternity-establishment for placement-eligible children. The Family-Support-Act-1988 created mandatory guideline rebuttable-presumption requirements, and the Federal-Case-Registry (FCR) plus State-Case-Registry (SCR) combined with the National-Directory-of-New-Hires (NDNH) deliver integrated locate-and-enforcement infrastructure. Methodology page documents how PlainChildSupport reconciles OCSE Annual Report aggregates with state-statute base-percentage tables and FCIC-style data-quality assertions.