The California legislature adopted an algebraic formula to calculate child support on July 1, 1992. The child support resulting from the use of the formula is presumed by the Court to be correct. To ensure accuracy, child support is usually calculated by a computer. The formula is as follows:

CS is the amount of child support;

K is a factor of both parent's income allocated for child support. This varies depending upon the number of children to be supported;

HN is the high earner's net monthly disposable income;

H% is the high-earner's approximate time of physical responsibility for the child (children);

TN is the parties' combined total monthly net disposable income.

Several deductions are allowed in computing net monthly income. Deductions include, state and federal income taxes, FICA contributions, union dues, retirement benefits, disability and health insurance premiums, and job related expenses. Child or spousal support actually paid under a court order to someone who is not a subject of the award being calculated may be deducted. In absence of a court order, child support paid in guideline amount for children not residing with the parent and are not the subject of the award being calculated may also be deducted. A "hardship," as defined by the Family Code, is not deducted from child support but is deducted from the income of the party with the hardship.

Although the presumption exists that the amount of child support determined by the formula is correct, the presumption may be rebutted by the factors as set forth in Family Code, Section 4057 (b) as follows:

1. The parties have stipulated to a different amount of child support (an agreement that the needs of the children are being adequately met along with other conditions) under Section 4065 (s).

2. The sale of the family residence is deferred and the rental value for the family residence in which the children reside exceeds the combined total of the mortgage payments, homeowner's insurance and property taxes. The amount of any adjustment pursuant to this paragraph shall not be greater than the excess amount.

3. The parent ordered to pay child support has an extraordinarily high income, and the amount determined under the formula would exceed the needs of the children.

4. A party is not contributing to the needs of the children at a level commensurate with the party's custodial time.

5. Application of the formula would be unjust or inappropriate, due to a special circumstance in a particular case. Special circumstances include, but are not limited to, the following:

• Cases in which the parents have different time-sharing arrangements for different children;
• Cases in which both parents have substantially equal time-sharing of the children, and one parent has a much lower or higher percentage of income used for housing that the other parent;
• Cases in which the children have special medical or other needs that could require child support to be greater than the formula amount.

It should be noted that, in addition to the amount of child support determined under the formula, additional child support may be ordered pursuant to Family Code, Section 4062. For instance, the court is mandated to order as additional child support child care costs related to employment or necessary education or training, and the reasonable uninsured health care costs for the children. The court may also order as additional child support costs related to education or special needs of the children and travel expenses for visitation. The manner in which theses expenses are computed and apportioned between the parties is governed by Family Code, Section 4061.

The Family Code also provides for a low-income adjustment. Generally, a payor whose net monthly disposable income is less than $1,000 may be ordered to pay less than the amount determined pursuant to the Family Code, Section 4055 formula.