First of all it depends on the state you live in, and then how much he makes. For example here in New York State it's 17% of the man's income for the first child. My former husband used to work hard and make good money during the Spring, Summer, and Fall, but when Winter came around he would be laid off for the season. He and his ex came to a mutual agreement that when he was laid off the amount would be dropped until he went back to work full time in the Spring and he would make up the difference at that point. I would suggest he try to work out an arrangement with her first. If they can't come to a compromise then it needs to be handled through an attorney, just make sure that child isn't the one getting the short end by either mom or dad. Because in the end that's what this is really about, the child's welfare.