Tex. Family Code § 154.131

(a) The child support guidelines are intended to guide the court in determining the amount of retroactive child support, if any, to be ordered.

(b) In ordering retroactive child support, the court shall consider the net resources of the obligor during the relevant time period and whether:

(1) the mother of the child had made any previous attempts to notify the obligor of his paternity or probable paternity;

(2) the obligor had knowledge of his paternity or probable paternity;

(3) the order of retroactive child support will impose an undue financial hardship on the obligor or the obligor's family; and

(4) the obligor has provided actual support or other necessaries before the filing of the action.

(c) It is presumed that a court order limiting the amount of retroactive child support to an amount that does not exceed the total amount of support that would have been due for the four years preceding the date the petition seeking support was filed is reasonable and in the best interest of the child.

(d) The presumption created under this section may be rebutted by evidence that the obligor:

(1) knew or should have known that the obligor was the father of the child for whom support is sought; and

(2) sought to avoid the establishment of a support obligation to the child.

(e) An order under this section limiting the amount of retroactive support does not constitute a variance from the guidelines requiring the court to make specific findings under Section 154.130.

(f) Notwithstanding any other provision of this subtitle, the court retains jurisdiction to render an order for retroactive child support in a suit if a petition requesting retroactive child support is filed not later than the fourth anniversary of the date of the child's 18th birthday.