How many times are you allowed to file child support modification papers? I agreed to more then 17% for my daughter and now I want to change my mind. One thing for the readers. when your child turns 21 you must go to court to make this change. If you don't and you think you are done paying, think again. Since I stop payment on my own she can go to court and get more money. Everything has to be done in court. I will be owning 40 weeks back child support even that my son is over 21. thanks Zucc