In determining whether or not to order child support and, if ordered, the amount of child support, the court must refer to the Statewide Uniform Child Support Guideline. There are various programs that will calculate the amount of child support, if any. The courts use "dissomaster". Their are other such calculation programs, but you need to make sure that they have been certified by the judiciary in order to use it in court. Your local law library will also have the program, and it is available online as well at www.childsup.ca.gov. Understand that both parents have a responsibility to support the child(ren). Some of the factors that the guidelines take into account are: (1) that a parent's first and principal obligtation is to support his/her minor children according to the parent's circumstances and station in life (Fam.C. section 4053(a)), (2) both parents are mutually responsible for the support of their children (Fam.C. Sec. 4053(b)), (3) each parents actual income and level of responsibility for the children (Fam.C. Sec 4053(c)), (4) each parent should pay for the support of the child(ren) according to his/her ability (Fam.C. Sec. 4053(d), (5) the interests of the children as the state's top priority (Fam.C. Sec. 4053(e)). There are more, but you get the gist. You can have two parents with equal custody time and one parent paying to the other child support. The idea is that the support is for the children. The state doesn't want the children to live like kings with one parent and like paupers with the other. That doesn't mean that it doesn't happen. The goal is to provide for the children. The reality is that the receiving parent, by virtue of have custody of the children during that time will also benefit. Try to think in terms of what you want for your children versus what you don't want for your ex. If your concern is that the children are not benefiting from the support, you may want to consider trying an out-of-court resolution through mediation or collaboration. The judge's hands are tied when it comes to child support. You and your ex, however, can create an agreement that meets the needs of the children to your satisfaction. Just remember, whatever agreement you reach, either or both of you can get "guideline" support at any time.
If the parents cannot reach an agreement about child support the Court will calculate Child support mostly based on THREE facts:the custodial time-share (who has the child(ren) how much of the time), and EACH PARENT'S income.
Even if the time-share is EXACTLY 50/50, a parent who earns substantially more than the other parent will probably be ordered to pay some amount of child support. If there is enough difference between the parents' incomes, the high-earner parent will even be ordered to pay child support to the other parent even though the high earner has the child(ren) more than 50% of the time.
There are online California state child support calculators available; for the best answer, however, you should review ALL of the facts of your situation with an experienced family law attorney.