Speak to local council but in interim this link may help. http://www.childsup.ca.gov/Resources/CalculateChildSupport.aspx
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There is the California "Guideliner" program - available as indicated at the www.ca.gov website. You can also look for "XSpouse", which has a demonstration version to give you an indication on what you should pay. California's child support guideline formula is a bit more complicated than comparative gross incomes & timeshare, since it's based upon how much after-tax money (net disposable income) you have available for support. If there's no court order then there's no enforceable obligation to pay support. California limits the retroactivity of child support to the date when the request is first served upon the obligated party (likely, you). As a suggestion, pay what the program(s) estimate is and you can avoid going to court on the issue.