How to Modify Child Support in Washington
Reviewed by DocDraft Legal Team · Washington · Last updated September 21, 2026
In Washington, a child support modification is a court or state agency changing the dollar amount of an existing child support order after your situation changes, and Washington stands out by also letting you adjust an order every 24 months without proving a substantial change, based on either parent's income or the state economic table (RCW 26.09.170(9)). Support in Washington follows a statewide schedule tied to both parents' income (chapter 26.19 RCW), so a job loss, a raise, or new medical or child care costs can make the current amount too high or too low. You have more than one path. You can petition the superior court that entered your order using the Petition to Modify Child Support Order (form FL Modify 501), or, when 24 months have passed and only income or the schedule has changed, use the shorter Motion to Adjust Child Support Order (form FL Modify 521). If the Division of Child Support handles your case, you can also ask it to review your order. You can petition on substantially changed circumstances at any time (RCW 26.09.170(5)). A change reaches back only to installments coming due after you file, not to when your circumstances changed (RCW 26.09.170(1)), so keep paying your current order until it is changed. Attorney review of your filing is available through DocDraft.
Find out where you stand in Washington
Where are you with changing your child support order?
DocDraft provides document preparation, not legal advice.
How do I modify child support in Washington?
File a Petition to Modify Child Support Order (form FL Modify 501) with the superior court that entered your order, showing substantially changed circumstances (RCW 26.09.170(5)). If 24 months have passed and only income or the state schedule changed, you can instead file a Motion to Adjust Child Support Order (form FL Modify 521).
How much does income have to change to modify child support in Washington?
Washington sets no single percentage. You can petition at any time on a substantial change in either parent's income or the child's needs (RCW 26.09.170(5)). Separately, after 24 months you may adjust the order without proving a substantial change, based on income changes or the state economic table (RCW 26.09.170(9)).
How far back can a child support change go in Washington?
A modification reaches only installments accruing after you file your petition or motion, not back to when your circumstances changed (RCW 26.09.170(1)). Support that already came due cannot be reduced, so filing promptly protects you. Keep paying your current order until the court or agency changes it.
Which court or agency handles child support modifications in Washington?
The superior court that entered your order handles court petitions and motions, usually through the family law department. If the Division of Child Support manages your case, you can ask it to review your order; court-order cases go through the county prosecutor, while administrative orders use a DCS petition.
Washington child support modification at a glance
In Washington, a child support modification changes the amount of an existing support order after your circumstances change, and you have several routes. You can petition the superior court on substantially changed circumstances at any time using the Petition to Modify Child Support Order (form FL Modify 501) (RCW 26.09.170(5)). Once 24 months have passed, you can adjust the order without proving a substantial change, based on income changes or the state economic table, using the Motion to Adjust Child Support Order (form FL Modify 521) (RCW 26.09.170(9)). Support follows a statewide schedule tied to both parents' income (chapter 26.19 RCW). If the Division of Child Support handles your case, it can review your order. A change reaches only installments accruing after you file (RCW 26.09.170(1)).
Adjusting a Washington order after 24 months
Suppose your Washington order was entered 25 months ago and both parents' incomes have shifted, but nothing else has changed. Because Washington lets you adjust an order every 24 months without proving a substantial change (RCW 26.09.170(9)), you can file the shorter Motion to Adjust Child Support Order (form FL Modify 521) rather than a full petition. You complete the child support worksheets with current pay information and file with the superior court that entered your order, then serve the other parent. Because the change reaches only installments accruing after you file (RCW 26.09.170(1)), you file promptly and keep paying the current amount until the court rules. The court recalculates support under the state schedule and signs the adjusted order. Attorney review of your filing is available through DocDraft.
Relevant Laws
RCW 26.09.170 (modification of a support order)
Governs modification of child support in Washington. Provisions may be modified only as to installments accruing after the petition or motion is filed (subsection 1), on substantially changed circumstances (subsection 5), and, once 24 months have passed, adjusted without a substantial change based on income or the economic table in chapter 26.19 RCW (subsection 9).
RCW 26.09.175 (procedure for modification of an order)
Sets out the procedure for modifying a child support order in Washington, including filing a petition and the mandatory child support worksheets, using the summons prescribed by the courts (form FL Modify 500), and serving the other party.
Chapter 26.19 RCW (Washington child support schedule)
Contains Washington's statewide child support schedule, economic table, and standards for calculating support from both parents' combined income, which the court and the Division of Child Support apply when recalculating an order.
Washington DCS: Child Support Modification
The Washington State Division of Child Support explains how to ask for a review of an order, when a court-order case must go through the county prosecutor, and when an administrative order uses a DCS petition for modification.
Regional Variances
Washington child support modification rules at a glance
Qualifying threshold
Washington uses no single percentage. You can petition at any time on substantially changed circumstances (RCW 26.09.170(5)), and after 24 months you can adjust the order without proving a substantial change, based on income changes or the state economic table (RCW 26.09.170(9)).
Where to file
The superior court that entered your order, usually the family law department. If the Division of Child Support handles your case, you can ask it to review the order; court-order cases go through the county prosecutor, while administrative orders use a DCS petition.
Modification form
The Petition to Modify Child Support Order (form FL Modify 501) with the Washington child support worksheets, or the Motion to Adjust Child Support Order (form FL Modify 521) for the 24-month path. These mandatory statewide forms are free on the Washington Courts website.
Retroactivity
A modification reaches only installments accruing after the petition or motion is filed, not back to when circumstances changed (RCW 26.09.170(1)). Support that already came due cannot be reduced.
Periodic review
Washington allows a 24-month adjustment without a substantial change (RCW 26.09.170(9)). If the Division of Child Support handles your case, you can generally request a review about every three years under federal rules, and sooner when circumstances change.
Suggested Compliance Checklist
Gather proof of your changed circumstances
Before you file days after startingCollect current pay stubs, tax returns, and proof of the change (job loss, income change, or new medical or child care costs), and estimate the new amount under the state schedule (chapter 26.19 RCW). Attorney review of your filing is available through DocDraft.
Decide between a petition and a 24-month motion
Before you file days after startingIf your circumstances changed substantially, plan to file a petition (RCW 26.09.170(5)). If 24 months have passed and only income or the state schedule changed, plan to file the shorter Motion to Adjust Child Support Order (form FL Modify 521) instead (RCW 26.09.170(9)).
Complete the Washington modification forms
As soon as your circumstances change days after startingFill out the Petition to Modify Child Support Order (form FL Modify 501) and the Washington State Child Support Schedule Worksheets, describing the change and your current income. Use the free mandatory forms on the Washington Courts website.
File with the superior court
Promptly (the change dates back to filing) days after startingFile your petition or motion and worksheets with the superior court clerk and pay the fee, or ask the court to waive it. Because a change reaches only installments accruing after you file, file promptly (RCW 26.09.170(1)).
Serve the other parent
After filing, before the hearing days after startingHave an adult who is not you serve the other parent with the summons (form FL Modify 500) and your filed papers, then file the proof of service (RCW 26.09.175). Proper service is required before the court can change the order.
Attend the hearing and get the new order
On your hearing date days after startingGo to the hearing with your income proof, let the court recalculate support under the state schedule, and get the signed order effective for installments accruing after you filed. Keep paying the current order until then.
| Task | Description | Document | Days after starting |
|---|---|---|---|
| Gather proof of your changed circumstances | Collect current pay stubs, tax returns, and proof of the change (job loss, income change, or new medical or child care costs), and estimate the new amount under the state schedule (chapter 26.19 RCW). Attorney review of your filing is available through DocDraft. | - | Before you file |
| Decide between a petition and a 24-month motion | If your circumstances changed substantially, plan to file a petition (RCW 26.09.170(5)). If 24 months have passed and only income or the state schedule changed, plan to file the shorter Motion to Adjust Child Support Order (form FL Modify 521) instead (RCW 26.09.170(9)). | - | Before you file |
| Complete the Washington modification forms | Fill out the Petition to Modify Child Support Order (form FL Modify 501) and the Washington State Child Support Schedule Worksheets, describing the change and your current income. Use the free mandatory forms on the Washington Courts website. | - | As soon as your circumstances change |
| File with the superior court | File your petition or motion and worksheets with the superior court clerk and pay the fee, or ask the court to waive it. Because a change reaches only installments accruing after you file, file promptly (RCW 26.09.170(1)). | - | Promptly (the change dates back to filing) |
| Serve the other parent | Have an adult who is not you serve the other parent with the summons (form FL Modify 500) and your filed papers, then file the proof of service (RCW 26.09.175). Proper service is required before the court can change the order. | - | After filing, before the hearing |
| Attend the hearing and get the new order | Go to the hearing with your income proof, let the court recalculate support under the state schedule, and get the signed order effective for installments accruing after you filed. Keep paying the current order until then. | - | On your hearing date |
Frequently Asked Questions
An involuntary income drop can support a modification, but you must file to change the amount; support keeps accruing at the old rate until the court or agency acts (RCW 26.09.170(1)). A court may consider whether you are earning what you reasonably could. Do not simply stop paying.
No. Either parent can file a petition or motion on their own, and the other parent is served and can respond (RCW 26.09.175). If both agree on a new amount, you can submit agreed worksheets and an order for a judge to review against the state schedule (chapter 26.19 RCW).
After you file, the superior court sets a hearing, often several weeks to a few months out depending on the county. An uncontested change or a 24-month motion to adjust can move faster. Because the change reaches only installments accruing after you file, filing promptly protects you (RCW 26.09.170(1)).
Yes. If the Division of Child Support handles your case, you can ask it to review your order after a change in income, medical, or child care costs. Court-order cases are handled through the county prosecutor, while administrative orders use a DCS petition for modification (RCW 26.09.170).
Once 24 months have passed since your order or last adjustment, you can adjust the amount without proving a substantial change, based on either parent's income or changes to the state economic table (RCW 26.09.170(9)). You file a Motion to Adjust Child Support Order (form FL Modify 521) with the worksheets.
A modification changes support only for installments accruing after you file (RCW 26.09.170(1)). Support that already came due, called arrears, generally cannot be reduced or erased by a modification. Keep paying your current order to avoid building arrears while your request is pending.
Filing in superior court carries the standard filing fee, but you can ask the court to waive it if you cannot afford it. A review through the Division of Child Support does not charge you a fee. The statewide forms and worksheets are free on the Washington Courts website.
For most changes you file the Petition to Modify Child Support Order (form FL Modify 501) with the Washington child support worksheets. If 24 months have passed and only income or the state schedule changed, use the Motion to Adjust Child Support Order (form FL Modify 521) instead.
Other Washington guides
Ready to Draft Your Document?
Get AI-powered legal documents with attorney review included. Plans start at $39.99/mo.