The two main factors for child support are income and timeshare. For income, the Court will look at the current gross monthly income of both parents. For timeshare, the Court will look at how much time each parent spends with the child. Other factors, such as deductions from pay (i.e. health insurance premiums, union dues, required retirement contributions), mortgage interest, property taxes and child support paid for a child from a different relationship, are also factored into the amount.
The Court looks at the current circumstances. However, if certain factors change in the future, child support can be modified. For example, if you obtain more time with your child or your income changes, child support will likely change as well. However, most importantly, child support does not automatically change. If your income changes, you must file a Request for Order immediately. This will allow the Court to make the order retroactive to the date you filed the Request for Order. The Court cannot go back any further.
For an estimate of child support, visit https://www.cse.ca.gov/ChildSupport/cse/guidelineCalculator.