Quick answer: Child support modification in Washington has several routes. You can petition on a substantial change of circumstances at any time, or ask for an adjustment with no change shown once 24 months have passed since the order or last adjustment. Support can change only for installments accruing after the petition or motion is filed.
This Washington child support modification calculator applies RCW 26.09.170. Enter your current order and the amount the schedule gives today (you can get it from the Washington child support calculator), say which route applies, and it shows whether the order qualifies and what the gap adds up to.
Washington child support modification at a glance
| Rule | What Washington says |
|---|---|
| Any time | A party may petition on a substantially changed circumstances at any time; voluntary unemployment alone is not one (RCW 26.09.170(5)) |
| 24 months | After 24 months from entry or the last adjustment, adjust for changes in income or the economic table without a substantial change; motion plus worksheets (26.09.170(9)) |
| One year or more | Severe economic hardship, support past 18 to finish high school, or adding an automatic adjustment clause (26.09.170(8)) |
| Phase-in | An adjustment of more than 30% that causes significant hardship may be made in two equal steps six months apart (26.09.170(9)(c)) |
| State agency | May file when the order is at least 15% above or below the standard calculation in assistance cases (26.09.170(10)) |
| Start date | Only installments accruing after the petition or motion (26.09.170(1)(a)) |
| Federal rule | Support already due cannot be modified retroactively (42 U.S.C. 666(a)(9)) |
How does child support modification work in Washington?
- Know the routes. See what counts as a substantial change in Washington.
- File with worksheets. See how to modify child support in Washington.
- Income problems and incarceration. See child support after job loss or incarceration in Washington and, for what stays owed, the Washington child support arrears calculator.
What does this modification calculator check?
The calculator tests the 24-month adjustment route and the substantial-change route, shows the monthly gap against the schedule amount, and flags the 15% and 30% lines the statute mentions. Washington sets no percentage for the two main routes, so it cannot say whether a court will find a change substantial.
Frequently asked questions
What do I have to show to modify Washington child support?
A substantial change of circumstances at any time, or no change at all once 24 months have passed since the order or last adjustment.
Is there a Washington percentage for child support modification?
Not for the two main routes; 15% matters for the state agency and 30% for phasing in a large adjustment.
From what date can Washington change child support?
Only for installments accruing after the petition or motion is filed.
Does a job loss count as a substantial change in Washington?
Voluntary unemployment or underemployment by itself does not; involuntary loss can.
Can I modify Washington support after one year for hardship?
Yes, if the order in practice works a severe economic hardship on either party or the child.