There is an online child support calculator at www.flcourts.org under FORMS. The children that you and he have together and live with do not give him any credit.
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The court will likely impute minimum wage to him if he is able to work. Your income will not be taken into account because you are not the mother of the child for whom support is being requested. He needs to make a really good effort to find a job if he isn't already.
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Previous-born children can sometimes qualify the payor for a slight decrease in the obligation to a later-born child. Make sure to bring the previous children's expenses to the judge's attention, as a downward deviation is, to a certain extent, a matter of judicial discretion.