Child support is designed to be dynamic. That is, it's supposed to go up and down as Mom's and Dad's incomes increase and decrease, as well as when there's a change in the cost of health insurance or child care. Here's what Rule 32(3)(b) says about changing child support:
(b) There shall be a rebuttable presumption that child support should be modified when the difference between the existing child support award and the amount determined by application of these guidelines varies more than ten percent (10%), unless the variation is due to the fact that the existing child support award resulted from a rebuttal of the guidelines and there has been no change in the circumstances that resulted in the rebuttal of the guidelines.