Interest on Child Support Arrears in Montana: Rate, Simple vs. Compound and When It Applies
Montana child support interest: we could not verify a fixed rate for support arrears. General judgments carry the prime rate plus 3%, simple, set each January 1, but sources disagree on whether that applies to support, so ask the court or the department.
Does Montana charge interest on child support arrears?
We could not verify a fixed statutory rate for support arrears. Part of the reason is that the support statutes we read mention interest only in passing: they list “fines, fees, penalties, interest” among amounts the department is authorized to collect by the same means as support, and they allow a support registry to record the interest included in a judgment for arrears, without stating a rate (MCA 40-5-201). Secondary websites disagree: some say 10% a year, others say none is automatic. We are not stating either.
What does the general judgment interest statute say?
Interest is payable on judgments recovered in Montana courts, and on the cost incurred to obtain or enforce a judgment, at the prime rate published by the Federal Reserve on the day judgment is entered plus 3%, not compounded; the prime rate is set as of January 1 each year and stays in effect until December 31 (MCA 25-9-205). Whether a support judgment gets that rate depends on the judgment and how the court or department applies it, so ask.
How could I test a Montana rate?
Enter one in the Montana arrears calculator. It uses simple interest from each due date, month by month.
| Scenario at 6% simple, no payments | Interest | Total owed |
|---|---|---|
| 12 unpaid installments of $500 | $165.00 | $6,165.00 |
| 24 unpaid installments of $500 | $690.00 | $12,690.00 |
| 36 unpaid installments of $500 | $1,575.00 | $19,575.00 |
These are illustrations, not a statement of the Montana rate.
What should I ask the Montana department?
Ask in writing whether interest, penalties or fees are included in the balance, what rate applies, from what date, and how payments are applied. The department is authorized to collect fines, fees, penalties and interest like support (40-5-201). Keep every statement.
Does a court have to order interest first?
The statutes we read do not say. Because the general judgment rate attaches to judgments recovered in the courts, a judgment that states interest is the clearest basis; ask the court to state the rate and start date in any judgment for arrears.
Do penalties or fees apply as well?
The statutes list fines, fees, penalties and interest among amounts the department may collect by the same procedures as support (MCA 40-5-201), but we did not find a schedule. Ask for an itemized statement showing each.
Is a missed payment treated as delinquent right away?
No. An obligor becomes delinquent 8 working days after the last day of the month in which the payment is due, which is when delinquency withholding can begin (40-5-412(1)(b)).
What if I disagree with the amount?
At a license hearing the only issues include the amount of the support debt and whether a delinquency exists (MCA 40-5-703), so bring your payment records. Outside that process, ask the court to determine the balance.
Where do you get the official figure?
From the Child Support Services Division or the clerk of court. See whether arrears expire or can be forgiven and file to modify if your circumstances changed.
Frequently asked questions
What is the Montana interest rate on child support arrears?
We could not verify a fixed rate for support arrears. General judgments carry prime plus 3%, simple.
Is Montana judgment interest compounded?
No. The statute says it may not be compounded.
When is the Montana judgment interest rate set?
As of January 1 each year, using the prime rate plus 3%.
When is a Montana child support payment delinquent?
Eight working days after the last day of the month it is due.
Where can I check my Montana child support balance?
With the Child Support Services Division or the clerk of court.
Official sources
- MCA 40-5-412: delinquency income withholding
- MCA 40-5-411: immediate income withholding
- MCA 40-5-701: license suspension definitions
- MCA 40-5-702: notice of intent to suspend
- MCA 40-5-704: suspension of licenses
- MCA 25-9-205: interest on judgments
- MCA 40-4-208: modification
- 15 U.S.C. 1673: restriction on garnishment
- 42 U.S.C. 652(k): denial of passports
- MCA 40-5-201: definitions
A local family law attorney can review your situation — many offer a free consultation.
This is general information, not legal advice. It is based on the cited Montana statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Montana attorney.