CAL. FAM. CODE § 4059 : California Code - Section 4059

The annual net disposable income of each parent shall be computed by deducting from his or her annual gross income the actual amounts attributable to the following items or other items permitted under this article:

(a) The state and federal income tax liability resulting from the parties' taxable income. Federal and state income tax deductions shall bear an accurate relationship to the tax status of the parties (that is, single, married, married filing separately, or head of household) and number of dependents. State and federal income taxes shall be those actually payable (not necessarily current withholding) after considering appropriate filing status, all available exclusions, deductions, and credits. Unless the parties stipulate otherwise, the tax effects of spousal support shall not be considered in determining the net disposable income of the parties for determining child support, but shall be considered in determining spousal support consistent with Chapter 3 (commencing with Section 4330) of Part 3.

(b) Deductions attributed to the employee's contribution or the self-employed worker's contribution pursuant to the Federal Insurance Contributions Act (FICA), or an amount not to exceed that allowed under FICA for persons not subject to FICA, provided that the deducted amount is used to secure retirement or disability benefits for the parent.

(c) Deductions for mandatory union dues and retirement benefits, provided that they are required as a condition of employment.

(d) Deductions for health insurance or health plan premiums for the parent and for any children the parent has an obligation to support and deductions for state disability insurance premiums.

(e) Any child or spousal support actually being paid by the parent pursuant to a court order, to or for the benefit of any person who is not a subject of the order to be established by the court. In the absence of a court order, any child support actually being paid, not to exceed the amount established by the guideline, for natural or adopted children of the parent not residing in that parent's home, who are not the subject of the order to be established by the court, and of whom the parent has a duty of support. Unless the parent proves payment of the support, no deduction shall be allowed under this subdivision.

(f) Job-related expenses, if allowed by the court after consideration of whether the expenses are necessary, the benefit to the employee, and any other relevant facts.

(g) A deduction for hardship, as defined by Sections 4070 to 4073, inclusive, and applicable published appellate court decisions. The amount of the hardship shall not be deducted from the amount of child support, but shall be deducted from the income of the party to whom it applies. In applying any hardship under paragraph (2) of subdivision (a) of Section 4071, the court shall seek to provide equity between competing child support orders. The Judicial Council shall develop a formula for calculating the maximum hardship deduction and shall submit it to the Legislature for its consideration on or before July 1, 1995.