In California, whether at OSC or Trial, child support is calculated by using a sophisticated computer software that is available to all members of the legal community and used by all family law judges. While there are a number of factors, the primary factors are fathers' gross income, mothers' gross income, and the percentage of time that each child spends with each parent. Other factors include mandatory deductions for health insurance, union dues and retirement. At trial, most judges also factor in monthly mortgage interest and property taxes for a primary residence.