Ordinarily, Missouri child support is subject to revision when financial circumstances change such that the child support amount by 20% or more. However, there must be an actual material change in financial circumstances since the time of the last order. This situation commonly occurs when the parties agree to a lower child support amount than the ordinary calculations, then later one party decides to return to court to lower or raise the child support amount. According to the Missouri Court of Appeals, a party who seeks to modify custody this way, once they have agreed to a different amount, bears the burden of showing the that parties' financial circumstances have actually changed sufficiently since the time of the last order. For such a case, see: http://www.courts.mo.gov/file.jsp?id=25121