The factors used in determined the monthly basic support obligation are the parties incomes including spousal support, , number and age of children, and health insurance cost coverage. The payment goes to the party who has the children living with them the majority of the time. Figuring out the worksheet can be tricky if a party has overtime or a bonus structure that is not regular. Further the income of other adults in the home can sometimes, but not usually be used.
Lately there has been a surge of requested Downward Deviations based on the obligated party having the children close to 50% of the time. WA is a progressive state at the moment and often awards shared parenting plans. The obligated party argues they should be ordered to pay less than the standard amount for having the children more. This is discretionary to the court and must be agreed upon or a decision maker needs to be convinced. So, it can be an expensive battle.