Materially and substantially changed is a phrase commonly used in the context of support determinations in domestic relations law, as well as various other contexts. There is no precise definition of this subjective term, but it is generally interpreted as a change which is significant and has a noticeable impact on the current situation. It is a change which is important in terms of value, degree, amount, or extent.
In the context of child support payments, a material and substantial change in circumstances may justify a request for payment modification. For example, a parent's loss of job or significant salary increase may be considered a material and substantial change. In another example, a child's enrollment in summer camp may be considered a material and substantial change. The interpretation of a material and substantial change varies and depends on the views of the person ulimately reponsible for making the determination, such as a judge.