Unless otherwise agreed to in your marital settlement agreement, child support should end when the child attains the age of 18 or graduates from high school, whichever occurs later. You can be compelled to pay through college if you agreed to that in your settlement documents.
Child support can be modified whenever the party’s income changes so that the calculation for support goes up or down by a significant amount. Usually 15% is considered sufficient for a change. But the change is set from the date of the new supplemental petition to modify support. She cannot go back multiple years.
The child support amount can be changed if there is a change in income, but it would not be retroactive, it would be as of the date of the latest motion for modification.
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.