Washington Child Support Calculator

How is Child Support Calculated in Washington?

Washington calculates child support by combining you and the other parent's monthly net incomes to determine a basic support amount from a state schedule. This total obligation is then divided between you both based on your individual percentage share of the combined income. This method is governed by the Revised Code of Washington (RCW) Chapter 26.19.

Understanding Shared Custody & Overnights

In Washington, a child support adjustment may apply when a child spends a significant amount of time with both parents, defined as 91 or more overnights per year with the parent who owes support. When this threshold is met, the court uses a specific 'residential split' or 'cross-credit' calculation outlined in RCW 26.19.075. This formula adjusts each parent's obligation based on the percentage of time the child spends in the other parent's home, which typically results in a lower support transfer payment.

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✓ Verified for 2026 Guidelines • Reviewed October 2026 by Harmoney

Washington Child Support Guidelines at a Glance

Guideline Model Income Shares Model
Governing Legal Authority RCW 26.19
Shared Custody Threshold 91 Overnights (Residential Time Credit)
Age Support Ends Age 18 (or completion of high school, whichever is later)
Modification Standard Substantial Change in Circumstances

Frequently Asked Questions about WA Child Support


At what age does child support end in WA?

Child support in Washington terminates when a child turns 18 or graduates from high school, whichever occurs last. As specified in RCW 26.19.090, support continues as long as the child is enrolled in high school and is dependent on the parents.

How is child support calculated if one parent is unemployed in WA?

The court will typically impute or 'attribute' income to an unemployed or underemployed parent based on their work history, skills, education, and local job market conditions. Under RCW 26.19.071(6), this ensures that child support is calculated based on a parent's earning capacity, not just their current income, unless there is a valid reason for unemployment.

How do I modify a child support order in WA?

You can modify a child support order in Washington by showing a 'substantial change in circumstances' since the last order was entered. Governed by RCW 26.09.170, this change could be a significant increase or decrease in either parent's income, a change in the child's needs, or a change in the residential schedule.

Does WA child support cover college expenses?

A Washington court has the authority to order a parent to contribute to a child's post-secondary college or vocational school expenses. Under RCW 26.19.090, the court considers factors like the parents' financial ability and the child's aptitude when deciding whether to order post-secondary educational support for a dependent child.

How does WA handle health insurance and childcare costs?

Health insurance premiums, extraordinary healthcare expenses, and work-related childcare costs are allocated between the parents in proportion to their share of the combined monthly net income. Per RCW 26.19.080, these expenses are added to the basic child support obligation to determine the total amount of support.