The court cannot use the income of a spouse or significant other in the calculation of child support (Family Code 4057.5). The income of the new spouse is used in the calculation of the parent’s net income for tax purposes only.
The bottom line is the fact the Ex remarried will have little to no effect on child support calculation.
The answer by Mr. Montgomery is excellent. The only point I would add is that the income of his new spouse will work to the benefit of your ex, not you. It is completely counter-intuitive, but here is the math (and the logic behind it). Although the new spouse income will not be considered directly, it can be considered because the income of his new spouse might put him into a higher tax bracket. If this is the case, the calculator will assume he has less money available for support, and it will reduce support accordingly. The more money his new spouse makes, the more of an effect it will have. Most experienced family law attorneys have been in the courtroom when someone in your position becomes insistent that the new spouse income be included, and it causes them to cringe. I just want you to know that it may not be in your best interest to spend any energy on that particular point.
A free online guideline calculator can be found by clicking on the following link: http://www.childsup.ca.gov/Resources/CalculateChildSupport/tabid/114/Default.aspx. My advice is to play with the numbers. Put in theoretical numbers for the new spouse income and see that this advice is accurate, as is that of Mr. Montgomery who points out that the effect will likely be very small, if any at all.Ask a similar question