Ohio Rev. Code § 3119.71: Modification of order relates back.

Except as otherwise provided in section 3119.772 of the Revised Code:

(A) If the obligor or obligee does not request a court hearing on the revised child support amount determined by the child support enforcement agency and filed with the court pursuant to section 3119.63 of the Revised Code and the court modifies the order to include the revised amount pursuant to section 3119.65 of the Revised Code, the modification shall relate back to the first day of the month following the date certain on which the review of the court child support order began pursuant to division (A) of section 3119.60 of the Revised Code.

(B) If the obligor or obligee requests a court hearing on the revised child support amount and the court, after conducting a hearing, modifies the court child support amount under the order, the modification shall relate back to the first day of the month following the date on which the review of the court child support order began pursuant to division (A) of section 3119.60 of the Revised Code.