Updated for 2026 guidelines
California Child Support Arrears Interest Calculator 2026
California charges 10 percent a year on unpaid support, simple interest on the principal. That is the highest verified arrears rate of any state we cover, and it makes old balances grow faster here than almost anywhere.
Reviewed by SupportDecode Editorial Team Page content reviewed Sources Methodology Update log
Estimate interest on a California arrears balance
Estimated arrears with interest: $5,500.00
Interest of $500.00 at 10% simple per year (Cal. Code Civ. Proc. 685.010).
| Line item | Amount |
|---|---|
| Arrears principalCode Civ. Proc. 685.010 (10% simple interest on money judgments) (California Legislature) | $5,000.00 |
| Simple interest at 10% per year for 12 month(s) (Cal. Code Civ. Proc. 685.010)Interest accrues at 10% per annum on the principal only (simple interest). Each missed support installment becomes a judgment by operation of law; the exact accrual-start citation (Fam. Code 17433.5 / CCP 685.020(b)) is official-confirmation-required. The 2023 reduced 5% rates for certain consumer medical and personal debt judgments do not apply to support.Code Civ. Proc. 685.010 (10% simple interest on money judgments) (California Legislature) | $500.00 |
| Arrears principal plus interestCode Civ. Proc. 685.010 (10% simple interest on money judgments) (California Legislature) | $5,500.00 |
Assumptions
- Accrual period expressed as 12 month(s); partial months prorate.
Estimate only. The court or state agency calculation controls.
California arrears interest under Cal. Code Civ. Proc. 685.010; rules last reviewed 2026-08-06.
Estimate only, and not certified for court use under California Rules of Court, rule 5.275. The county child support agency ledger, which credits every payment on its date, is the enforceable balance.
How interest on California arrears works
Every missed support payment in California becomes an enforceable money judgment automatically, by operation of law, the moment it comes due unpaid. No one has to go to court to turn the arrears into a judgment; the installment already is one.
Money judgments in California bear interest at 10 percent per year under Code of Civil Procedure section 685.010, and the statute applies the rate to the principal amount remaining unsatisfied. Interest on principal only means simple interest: the 10 percent never compounds, so interest does not earn interest.
Simple or not, 10 percent is steep. A $10,000 arrears balance left alone for five years accrues about $5,000 of interest on top. Payments and enforcement collections change the arithmetic month to month, which is why the county child support agency ledger, not any calculator, is the balance that counts.
One nuance we flag honestly: interest on each installment starts running from when that installment fell due, so a real balance is a stack of small judgments of different ages, each with its own interest clock. This tool applies one rate to one principal over one period, which is a simplification. The exact statutory accrual-start citation is one we have marked for official confirmation before we state it as settled.
The 2023 amendments that created reduced 5 percent rates for certain consumer medical and personal debt judgments do not apply here. Support judgments stay at 10 percent.
- Interest rate on arrears
- 10% per year, simple (interest accrues on principal only)source
- Statute
- Code Civ. Proc. § 685.010 (rate); § 685.020(b) (installment accrual)source
- How arrears become judgments
- Each missed installment is a judgment by operation of lawsource
- Reduced 5% rates (2023 law)
- Apply to certain consumer debt judgments only, never to supportsource
How to use this estimate
Enter the arrears principal and how long it has gone unpaid, in months or with a date range. The tool applies 10 percent simple interest for that period and shows the principal, the interest, and the total, each as its own line.
Because real balances accrue installment by installment, a single-period estimate runs high if much of the balance is recent and low if payments have been trickling in. For a court-ready audit, ask the local child support agency for a payment history and arrears calculation; their ledger controls.
If you are comparing states, keep the compounding difference in mind. Some states compound their arrears interest; California does not, so a lower compounded rate elsewhere can outgrow California’s flat 10 percent over long periods.
What this estimate includes
- Simple interest at the verified 10% annual rate of CCP § 685.010
- A month-count or date-range accrual period, with partial years prorated
- Separate principal, interest, and total lines with the statutory citation
What it leaves out
- Installment-by-installment accrual from each payment due date
- Payments, tax refund intercepts, and other collections during the period
- Interest a court has already reduced to a specific sum in your case
- The state ledger balance, which is the enforceable figure
California arrears FAQs
What interest rate applies to unpaid child support in California?
10 percent per year, the legal rate for money judgments under Code of Civil Procedure section 685.010. It applies because each unpaid support installment becomes a money judgment automatically when it comes due. Among the 51 states we have researched, it is the highest verified arrears rate.
Is California arrears interest simple or compound?
Simple. The statute says interest accrues on the principal amount remaining unsatisfied, so accrued interest never itself earns interest. A $10,000 balance accrues $1,000 a year, every year, until principal is paid down.
When does interest start running on a missed payment?
From the installment’s own due date forward, because each installment becomes a judgment when it falls due. That means a multi-year balance is really many small judgments with different start dates. Our single-period math simplifies that, and we have marked the exact accrual-start citation for official confirmation rather than overstating it.
Can California arrears interest be waived?
Courts cannot retroactively modify support that already came due, and interest on arrears is generally owed as a matter of law. The state has a compromise program for arrears owed to the government in some circumstances, and a parent owed money can agree to settle. Whether either path fits a real case is a question for the agency or a lawyer, not this page.
Why does my agency statement differ from this estimate?
Because the agency computes interest installment by installment, credits every payment on the day it arrived, and applies collections in a set order. A one-line estimate cannot reproduce that ledger. Treat this tool as a way to see the scale of 10 percent simple interest, then get the official arrears figure from the county child support agency.
Did the 2023 interest-rate reform lower the rate on support arrears?
No. The 2023 amendments created reduced 5 percent rates for certain consumer medical and personal debt judgments. Support judgments were not included, so child support arrears stay at the full 10 percent.
Official sources
Official sources last verified: .
- Code Civ. Proc. 685.010 (10% simple interest on money judgments)
California Legislature Last checked
- Code Civ. Proc. 685.020 (interest accrual date; (b) installment judgments accrue interest as each installment falls due)
California Legislature Last checked
Reviewed by SupportDecode Editorial Team Page content reviewed Sources Methodology Update log
Changelog: page first published with the 10 percent simple interest rule and the installment-judgment nuance. Material changes are dated in the update log.