When the Court determines child support, they utilize the computer program Dissomaster or ExSpouse, generally in California. There are various systems available online which can assist you in calculating what your child support will be, but you won't really know for sure what the sum will be, because the Judge has discretion on certain factors. As a general rule, however, there are very few factors which will cause your support to go up and down. They are: You and your ex's wages (wages are entered as monthly gross or pre-tax or pre-deduction wages); the timeshare each party has with the child(ren); who claims the child(ren) as deductions for tax purposes; deductible mortgage interest; union dues; health insurance payments; mandatory retirement payments; and new spouse income. The court may also grant a hardship deduction to a party for any other children which are supported and who are not from the relationship at issue.
Many parties are confused about the new spouse income and believe that any monies their new spouse earns will be counted as part of their income. This is not the case in California. Caselaw has established that counting the new spouse income as part of that parties income and therefore raising (or lowering) that parties spousal support to their detriment, was having the effect of discouraging marriage in California, so the law was changed. Courts no longer count new spouse income as part of your income, now it is only used to determine your tax filing bracket, if you are filing taxes with your new spouse. The effect, generally is, that the more your new spouse earns, the less you have to pay (or the more you will recieve) in child support, because it pushes you into a higher tax bracket (if you file taxes with your new spouse), and thus you have less disposable income to pay for your children's needs because you pay more in taxes. The theory behind this appropriate change in the law is that it is not your new spouse's financial responsibility to support the children you have with a former partner.