I believe the guidelines for child support in California are pretty cut and dried, they use a set formula. There are calculators online but I don't know how reliable they are. A better, more reliable approach might be to go to an attorney and see if they'll run the numbers through the computer program recognized by the courts (called Disso-master). That will spit out a number, and I believe in almost every case the court will simply use the number it spits out--so you can avoid a lot of additional angst and expense by just agreeing to the number.
Neither your remarriage or your ex's additional kids should impact child support. The stepfather isn't responsible for your daughter, her father is. And the court would look at his having additional kids as a responsibility he took on voluntarily, which doesn't impact his responsibility to his existing kid. So the only real considerations in the calculation are your individual disposable income and your ex's.
If you use a family law attorney as a consultant (working for both of you, not representing either of you individually) you should get accurate answers without a lot of argument. The attorney could give your husband a good idea of what would happen if you took the matter to court. And shouldn't cost more than a couple of attorney hours of work to get a resolution.
Your county may also have Family Law Facilitators available who could help you with this for free--check your county family law court website.
Edited by TJMH (08/09/16 11:04 PM)