How to Modify Child Support in Washington: Filing Steps and Effective Date
To modify Washington child support, file a petition or a motion for adjustment with worksheets and serve the other parent. The change reaches only installments after filing, so file as soon as your circumstances change.
How do you modify child support in Washington?
- Run the schedule amount in the Washington child support calculator and test it in the modification calculator.
- Choose the route. A motion for adjustment with worksheets after 24 months, or a petition for modification on a substantial change (RCW 26.09.170(5), (9)).
- File and serve. The date of filing sets the start; only later installments can change (26.09.170(1)(a)).
- Attach worksheets and income records. The schedule is the basis for any adjustment.
- Keep paying the existing order until the court changes it.
Who can start a Washington modification?
Either parent; and the Department of Social and Health Services may file an action to modify or adjust if public assistance is being paid for the child and its review finds the order at least 15% above or below the standard calculation, or in some non-assistance cases that meet its criteria and a party or another state asked for review (26.09.170(10)-(11)).
Why does the filing date matter in Washington?
Because modification reaches only installments accruing after the petition or motion (26.09.170(1)(a)). A change in January and a filing in July leaves six months at the old amount.
Can I ask for the adjustment on my own, without a lawyer?
Either party may start the 24-month adjustment by filing a motion and child support worksheets (26.09.170(9)(b)). A licensed Washington attorney can tell you whether to use that route or a petition.
What if my last adjustment was less than 24 months ago?
Then use the substantial-change route, or wait: 24 months must pass from the entry or the last adjustment or modification, whichever is later, and after a two-step phase-in, 24 months must pass after the second change (26.09.170(9)(a), (c)).
Should I keep copies of what I file?
Yes. Keep the filed motion, worksheets and proof of the filing date, since the date sets which installments can change.
Does the court have to use the schedule?
The schedule is the basis for adjustments under the 24-month route and automatic adjustment clauses (RCW 26.09.100(2)), but for postsecondary support it is advisory only (26.19.090). Bring worksheets either way.
Can a Washington hearing be remote?
If testimony other than an affidavit is required, a Washington court shall let a party or witness testify under penalty of perjury by telephone, audiovisual or other electronic means unless good cause is shown (26.09.170(12)).
What does the court do with automatic adjustments?
If the decree requires automatic periodic adjustments, they use chapter 26.19 as the basis and may happen more often than the timing in 26.09.170; the court can modify such a provision for economic hardship (26.09.100(2), (4)).
Can Washington parents agree to a different amount?
A support order stays in force until the court changes it. Ask the court to approve any agreed change so the amount you owe is not left in doubt.
How much does a late filing cost? An example
If you file 3, 6 or 9 months after your change, the relief you lose at a $300 monthly difference is:
| Delay before filing | Relief lost |
|---|---|
| 3 months | $900 |
| 6 months | $1,800 |
| 9 months | $2,700 |
What happens to unpaid support while the case is pending?
It stays owed as a judgment with interest. See whether Washington arrears expire or can be forgiven and add up your balance.
Frequently asked questions
How do I modify child support in Washington?
File a petition or a motion for adjustment with worksheets, and serve the other party.
Can the Washington state agency modify child support?
Yes, in assistance cases when the order is at least 15% off the standard calculation, and in some other cases.
When does a Washington modification take effect?
For installments accruing after the petition or motion.
Can I testify by video in a Washington modification?
Yes, unless good cause is shown otherwise.
Does a Washington modification stop income withholding?
Not until the court enters the new order.
Official sources
- RCW 26.09.170: modification of decree for maintenance or support
- RCW 26.09.100: automatic periodic adjustments
- RCW 26.09.320: abatement during incarceration
- 42 U.S.C. 666(a)(9): no retroactive modification of support already due
- 45 CFR 302.56: federal guideline requirements
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 Washington statutes, rules and court opinions, and every case turns on its own facts. Confirm how the law applies to your situation with a licensed Washington attorney.