Parents who have their children living with them after separation can apply for child support at any time. Usually they apply right after they separate or as part of their divorce application. They often apply for custody and child support at the same time. It is usually best to deal with these matters as early as possible.
Sometimes parents with custody do not want or need child support at first, but later their situation changes. They can apply for child support when the need occurs, even after a divorce and all other matters arising from the separation have been settled.
But if a step-parent is asked to pay support, the more time that has passed since the step-parent had an ongoing relationship with the child, the less likely it is that the court will order support payments. This is especially true if the step-parent’s social and emotional relationship with the child has ended.
A parent can apply for custody and support even while living separately under the same roof after their relationship with the other parent is over. But usually the court will not make any order for custody and support until one parent has actually moved out.