A support modification is a court-approved change to an existing child support order. In Washington a modification requires showing a substantial change in circumstances — typically a 15% or more change in either parent's net income under RCW 26.09.170.
RCW 26.09.170 governs modification of child support orders in Washington. A substantial change in circumstances is required. Washington presumes a substantial change exists when the order would change by 15% or more based on current income.
Income changes: Either parent's income increases or decreases by 15% or more since the last order. A parent loses employment involuntarily. A parent receives a significant promotion or change in employment. Understanding this term is important when completing your child support calculation. Use our worksheet calculator to see how this applies to your case.
Expense changes: Childcare costs change substantially when a child starts or leaves daycare. Healthcare costs change significantly. A child develops special medical needs.
Residential changes: The residential schedule changes substantially. A child moves to a different primary parent. A child reaches age 18 or graduates high school.
A successful modification replaces the existing order with a new one. The new order is effective from the date of filing the petition in most cases — not from the date of the hearing. File promptly when circumstances change.
There is no minimum waiting period. A modification can be requested any time there is a substantial change in circumstances. However courts discourage frequent filings without meaningful changes.
Use our 2026 Washington State estimator to see how these legal terms impact your support amount. All calculators are RCW 26.19 compliant.