How Washington Calculates Child Support
Washington uses the Income Shares model for child support. The governing law is Revised Code of Washington Section 26.19.020, along with the Washington State Child Support Schedule. Washington uses net income as the basis for its calculation and combines both parents' incomes to determine the total obligation. Each parent then contributes their proportional share.
Washington has no state income tax on wages or salaries. Workers in Washington pay only federal income taxes and FICA on their earned income, which means net income is higher relative to gross income than in most states. Because Washington's formula uses net income, this raises the formula input compared with a high-tax state, which is worth noting for parents comparing their overall financial picture.
One exception for high-income parents: Washington imposes a 7 percent capital gains tax on long-term capital gains above $262,000 per year. For parents with significant investment income, this tax affects their net financial position and is subtracted when working out net income for the formula.
The Washington Child Support Formula
Washington's calculation follows four steps.
Step one is determining each parent's monthly net income. Step two is combining both net incomes to produce the combined monthly net income. Step three is finding the Basic Support Obligation in Washington's schedule using the combined income and number of children. Step four is calculating each parent's income share percentage and applying it to the obligation.
A practical example: Parent A earns $5,000 per month. Parent B earns $2,500 per month. Combined income is $7,500. Parent A's income share is 66.7 percent. If Washington's schedule sets the Basic Support Obligation at $1,350 for two children at $7,500 combined income, Parent A's base obligation is $900 per month before residential time adjustments and add-ons.
Washington's schedule covers a range of combined income levels. At combined incomes above the schedule maximum, courts set support based on the children's reasonable needs and each parent's financial resources.
What Counts as Income in Washington
Washington uses a comprehensive income definition. Courts include wages, salaries, commissions, bonuses, overtime, self-employment income, rental income, pension and retirement distributions, Social Security benefits, SSDI payments, unemployment compensation, workers' compensation, and income from any other regular source.
Courts can impute income to a parent who is voluntarily unemployed or underemployed based on work history, education, skills, and the local job market.
Washington allows deductions from income before combining incomes: court-ordered child support currently being paid for children from other relationships and court-ordered maintenance from prior orders. These deductions reduce each parent's net income before the proportional shares are calculated.
Washington excludes means-tested public assistance and child support received for children from other relationships from the income calculation.
Step-by-Step: How to Use This Calculator
Step 1. Get your net monthly income. Start with gross income from wages, self-employment, rentals, regular capital gains and other sources, then subtract federal income tax, Social Security, Medicare and other deductions allowed by RCW 26.19.071. Washington has no state income tax on wages to subtract.
Step 2. Subtract existing court-ordered obligations (child support or maintenance from prior orders) from your net income.
Step 3. Estimate the other parent's net monthly income using the same method.
Step 4. Enter the number of children covered by this order.
Step 5. Enter your residential time percentage. Washington uses the term residential time rather than overnights, but the calculation is the same. Count the nights the children spend with you per year and divide by 365. Washington applies a residential time credit when the non-primary residential parent has at least 25 percent of residential time, approximately 91 nights per year.
Step 6. Add healthcare costs. Enter the monthly premium for the children's health insurance.
Step 7. Add childcare costs. Enter monthly work-related childcare expenses.
Step 8. Review the full breakdown before accepting the result.
Residential Time Adjustments in Washington
Washington applies a residential time credit when the non-primary residential parent has at least 25 percent of residential time, approximately 91 nights per year. Below that threshold, the standard Income Shares formula applies with no reduction.
At 25 percent of residential time and above, Washington reduces the paying parent's obligation to reflect the direct costs they bear during their time with the children. The credit scales upward as residential time increases toward 50 percent.
At near-equal residential time, both parents' obligations are evaluated and the higher earner pays the net difference to the lower earner. Washington courts recognize that equal residential time with meaningfully different incomes still produces a net payment from the higher earner to the lower earner.
The 25-percent threshold is a firm line. If your residential time is close to 91 nights per year, an accurate count matters. Moving across that threshold triggers the credit.
Add-On Expenses in Washington
Washington adds healthcare premiums and work-related childcare costs to the base obligation, allocated proportionally by income share. Courts may also address extraordinary medical expenses and educational costs on a case-by-case basis.
Washington courts can address transportation costs for residential time in long-distance arrangements. When one parent has relocated significantly, courts may allocate travel costs between the parents or factor them into a deviation.
Reading Your Results
The results display shows each parent's net income, combined net income, the Basic Support Obligation from Washington's schedule, income share percentages, the residential time credit if applicable, add-on costs, and the final monthly obligation.
If you have capital gains income that varies significantly from year to year, use a two-year average to produce a stable and accurate income figure. Single-year capital gains spikes can distort the result significantly.
After You Get Your Estimate
Washington courts follow the RCW 26.19 guidelines in all standard cases. Deviation is allowed when the guideline amount would be unjust or inappropriate based on written findings. Courts consider both parents' financial resources, the child's specific needs, the residential schedule, and any special circumstances.
Modification in Washington requires a substantial change in circumstances. A 25 percent or more change in the calculated obligation is Washington's statutory threshold for presumptive modification eligibility. Income changes, shifts in residential time past the 25-percent credit threshold, and changes in healthcare or childcare costs are the most common grounds.
A licensed Washington family law attorney can review your calculation and advise on residential time credits or modifications. Many offer a free initial consultation.