Child support arrears in California don’t just sit there. They grow. By statute, unpaid child support accrues 10% simple interest per year on the unpaid balance — the same rate as a court judgment. Most custodial parents are tracking the principal but not the interest. The actual amount owed is frequently larger than they realize.
How the Calculation Works
Interest accrues on each missed payment from the date it was due. A $1,500/month payment missed in January 2023 has been accruing 10% annual interest since then. By April 2026, that single missed payment has grown to approximately $1,950. Multiply that across three years of missed payments, and the total owed — principal plus interest — is substantially more than the sum of missed payments alone.
Calculating this correctly requires running the interest calculation on each missed payment separately from its due date. The California Child Support Recovery System includes the arrears calculator and the Claude AI prompt to run your specific numbers and produce a complete demand amount.
Educational use only. Not legal advice. Justice Foundation.
California Child Support Recovery System 
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