Effective January 1, 2011 the method for calculating child support changes for parents who have their children 20% to 39% of the overnights each year. The old law reduced child support for parents with 146 overnights or more per year.  Now parents with only 73 overnights can get a break. Although not yet tested in the courts , the change in the law alone may be reason enough for a parent to have his or her child support recalculated.