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Disclaimer: Interest is estimated as simple interest over the average age of missed payments; state rates range from 0% to 12% and some compound. Agency statements govern. Not legal advice.
Unpaid child support is not ordinary debt. Under the federal Bradley Amendment (42 U.S.C. §666(a)(9)), every missed payment vests as a final money judgment the day it falls due — no court can retroactively reduce it, regardless of job loss, disability, or informal agreements between the parents. Arrears survive bankruptcy (11 U.S.C. §523(a)(5) makes domestic support obligations non-dischargeable), rarely face a statute of limitations, and in most states grow with interest — 10% simple in California, 12% in Vermont, 10% compounded monthly in Colorado, and 0% in roughly a third of states.
Every state runs a child support enforcement agency under Title IV-D of the Social Security Act, and the toolkit is formidable: income withholding orders that garnish up to 50–65% of disposable wages under the Consumer Credit Protection Act, federal and state tax refund interception, bank levies, property liens, suspension of driver's and professional licenses, passport denial once arrears hit $2,500, credit bureau reporting, and contempt proceedings that can jail willful non-payors. Crossing state lines does not help — UIFSA makes orders enforceable nationwide, and willful interstate non-payment can be prosecuted federally under the Deadbeat Parents Punishment Act.
An order requires $900/month. The payor misses 24 months and makes $4,000 in partial payments. Principal arrears: 24 × $900 − $4,000 = $17,600. In a 10% simple-interest state, interest over the average 12-month age of the missed payments adds roughly $1,760, bringing the total near $19,400 — every dollar of it a vested judgment subject to wage withholding and license suspension.
Payors in financial trouble must petition to modify before arrears build — relief runs only from the filing date. Recipients should open a IV-D case early and get advice on interest judgments and lump-sum settlement structures. Either side facing a contempt hearing, license suspension, or an interstate enforcement action needs counsel: the procedural rules are technical and the stakes include incarceration.
Explore more free tools on our Family Law Calculators hub, walk through our interactive Family Law Wizards to understand your situation step by step, or contact LexScale.ai to build calculators like this for your own law firm website.
Enter the monthly amount ordered, the number of months missed, the total of any partial payments actually made, and the applicable interest rate on the arrears. The tool computes the principal arrears (ordered amounts minus payments), applies simple interest over the average age of the missed payments, and totals what is owing. Enforcement agencies calculate interest payment-by-payment, so their statement will differ modestly from this average-period estimate — but the output is close enough to plan around.
Two practical truths dominate arrears cases. First, arrears almost never disappear: courts rarely cancel support debt retroactively unless the payor proves they genuinely could not pay when each payment fell due — losing a job and never applying to vary the order is not enough. Second, the sooner a struggling payor applies to change the order, the better: a variation generally reaches back only to the application date. A payor whose income has truly dropped should file immediately and keep paying something; a recipient owed arrears should register with the enforcement agency early, because agencies collect far more effectively than informal chasing.
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