Washington State Child Support Calculation Guide for 2026

Disclaimer: This guide explains Washington State's 2026 child support calculation methodology for educational purposes. It is not legal advice.

Ask most people how child support is calculated and you'll get a shrug or a vague answer about "following a formula." The truth is, there's a very specific, legally-mandated process that Washington courts follow, and once you understand it, a lot of the confusion and anxiety around child support goes away.

This guide walks through the entire calculation from beginning to end, with a real worked example so you can follow along with your own numbers. By the end, you'll understand exactly where every dollar of a support order comes from, and what you can and can't change about it.

The Foundation: Washington's Income Shares Model

Washington operates on the Income Shares Model, which is used by the majority of U.S. States. The philosophical core of this model is that children should receive the same percentage of parental income they would have received if their parents had stayed together.

In practical terms, this means Washington doesn't just look at what the non-custodial parent earns. It looks at both parents' incomes, combines them, determines what percentage each parent contributes, and then makes each parent responsible for that same percentage of the children's total costs.

Official rules are published by the Washington Administrative Office of the Courts and codified in RCW 26.19.

Step 1: Determine Each Parent's Gross Monthly Income

Washington defines gross income broadly. It includes virtually everything you receive:

• Wages, salaries, commissions, and tips
• Overtime (but averaged over a 12-month period, not just a banner month)
• Self-employment income (gross revenue minus legitimate business expenses)
• Rental income (after maintenance costs)
• Unemployment compensation
• Disability and workers' compensation benefits
• Social Security or pension benefits paid on behalf of the children are credited against the obligation

What's not included: income of a new spouse or domestic partner, public assistance benefits like TANF or food stamps, and certain means-tested Social Security payments.

Step 2: Calculate Monthly Net Income

From gross income, you subtract only the legally-permitted deductions under RCW 26.19.071:

• Federal income taxes based on actual filing status
• State income taxes (Washington has none, but other state withholding may apply)
• FICA taxes (Social Security 6.2% + Medicare 1.45%)
• Medicare surcharge if applicable
• Mandatory pension or retirement contributions required by the employer as a condition of employment (not voluntary 401k contributions)
• Union dues actually paid
• State industrial insurance (L&I) premiums
• Health and dental insurance premiums paid for the children
• Actual payments on court-ordered child support or maintenance for other children

Not deductible: credit cards, car loans, student loans, voluntary retirement contributions, personal health insurance (only the children's portion), or any debt not listed above. Courts hear arguments about debt obligations regularly and rarely grant credit for them.

Step 3: Look Up the Basic Support Obligation

Once you have both parents' monthly net incomes, add them together, that's your combined monthly net income. Then look up the corresponding amount in the 2026 Washington Child Support Economic Table based on the number of children.

For example, at a combined income of $7,000/month for two children, the 2026 table shows a basic obligation of approximately $1,440/month. This is the total amount, not what either parent pays individually. That comes next.

Use our calculator to look this up instantly for your specific income and child count.

Step 4: Calculate Each Parent's Proportional Share

Now divide. If Parent A earns $4,500 net and Parent B earns $2,500 net, combined is $7,000. Parent A's share: $4,500 ÷ $7,000 = 64.3%. Parent B's share: 35.7%.

Each parent is responsible for their percentage of the basic obligation. Parent A owes 64.3% × $1,440 = $926/month. Parent B owes 35.7% × $1,440 = $514/month.

The parent with fewer residential days typically pays their share as a transfer payment to the other parent. If Parent A has the children 70% of the time, Parent B makes the monthly transfer payment of $514.

Step 5: Add Extraordinary Expenses

The basic obligation covers only food, ordinary clothing, and shelter. Everything else is calculated separately:

Work-Related Childcare

Say daycare costs $1,600/month. That cost is split according to the same 64.3/35.7 proportional split: Parent A owes $1,029, Parent B owes $571. These amounts go through the same payment system as the base support amount, they're not optional and don't disappear if a parent thinks childcare is "too expensive."

Health Insurance Premiums

The cost of the children's health insurance is added to the worksheet and split proportionally. Whoever pays the premium gets credited for it; the other parent's share is factored into their transfer obligation.

Uninsured Medical Expenses

Copays, prescription costs, orthodontics, these are split proportionally and typically paid within 30 days of the expense being incurred.

Step 6: Apply the SSR and 45% Cap Checks

Before the order is finalized, the court performs two safety checks:

• SSR Check: Will the paying parent retain at least approximately $2,394/month after this payment? If not, the obligation must be reduced.
• 45% Cap Check: Does the total obligation (base + extraordinary expenses) exceed 45% of the paying parent's net income? If yes, there needs to be a "good cause" finding for the court to approve it.

A Complete Worked Example

Let's pull this all together. Parent A nets $5,000/month. Parent B nets $3,000/month. Two children. Monthly daycare is $1,800.

1. Combined income: $8,000
2. Basic obligation at $8,000 / 2 children (from 2026 table): ~$1,560
3. Parent A's share (62.5%): $975
4. Parent B's share (37.5%): $585
5. Parent A pays daycare: 62.5% × $1,800 = $1,125
6. Parent B pays daycare: 37.5% × $1,800 = $675
7. SSR check: $5,000 - $975 transfer = $4,025 remaining. Passes.
8. 45% check: $975 = 19.5% of $5,000. Passes.

If Parent B (the lower earner) has the children less often and is making the transfer payment: $585 base + credit for their $675 daycare share = complex math best handled by our Worksheet Wizard, which automatically handles these calculations.

Related Articles

• SSR: The approximately $2,394 Floor Explained
• How Courts Decide Your Final Order
• 2026 Guidelines: The Complete Handbook

Conclusion

The calculation process is actually quite logical once you see it laid out step by step. Knowing the math before you go to court is one of the most practical advantages you can have, it tells you exactly what to fight for and what to accept. Run your specific numbers through our quick calculator now, then use the Professional Wizard to generate the complete worksheet.

For official state resources and documentation, please visit the Washington DSHS or the Washington Courts homepage.