Ohio Revised Code Title LIII. Real Property § 5322.05

(A) Subject to division (B) of this section, a reasonable late fee may be imposed and collected by an owner for each service period that an occupant does not pay rent when due under a rental agreement, provided that the due date for the rental payment is not earlier than the day before the first day of the service period to which the rental payment applies. However, no late fee shall be imposed or collected if the occupant makes a rental payment in full by the third day after the due date under the rental agreement.

(B) No late fee may be collected pursuant to division (A) of this section unless the amount of that fee and the conditions for imposing that fee are stated in the rental agreement or an addendum to that agreement.

(C) For purposes of division (A) of this section, a late fee of twenty dollars for each late rental payment, or twenty per cent of the amount of each late rental payment, whichever is greater, is deemed reasonable and does not constitute a penalty. However, the contract may provide for a late fee in a greater amount if that amount is reasonable. The owner has the burden of proof that the late fee in the greater amount is reasonable.

(D) Any reasonable expense incurred in rent collection or lien enforcement by an owner may be charged to the occupant in addition to the late fees permitted by this section.