A proportional share is each parent's percentage of the combined net income. This percentage determines each parent's share of the basic obligation and all extraordinary expenses including healthcare and daycare.
RCW 26.19.080(1): The basic child support obligation shall be allocated between the parents based on each parent's share of the combined monthly net income. Line 6 of the WSCSS worksheet records each parent's proportional share.
Formula: Parent share % = Parent net income ÷ Combined net income
Example: P1 net: $7,000 / P2 net: $3,000, Combined: $10,000
P1 share: $7,000 ÷ $10,000 = 70%, P2 share: $3,000 ÷ $10,000 = 30%
Both percentages must always add up to 100%.
Your proportional share percentage determines your obligation for both basic support and all extraordinary expenses. It is recalculated every time either parent's net income changes. A modification that changes income will change the proportional share percentages for both parents simultaneously.
Yes. Any substantial income change of 15% or more can trigger a modification that recalculates both parents' proportional shares and adjusts the transfer payment.
Yes. The same Line 6 percentages apply to all extraordinary expenses including healthcare premiums, daycare, education, and long-distance transportation costs.
Washington uses a monthly average of annual income. Divide annual income by 12 to get the monthly figure used for the proportional share calculation.
Use our 2026 Washington State estimator to see how these legal terms impact your support amount. All calculators are RCW 26.19 compliant.