Tennessee Code Title 36. Domestic Relations § 36-6-410

(a) Solely for the purpose of all other state and federal statutes and any applicable policies of insurance that require a designation or determination of custody, a parenting plan must designate the parent with whom the child is scheduled to reside a majority of the time as the primary residential parent of the child; provided, that this designation shall not affect either parent's rights and responsibilities under the parenting plan. In the absence of such a designation, the parent with whom the child is scheduled to reside a majority of the time is deemed to be the primary residential parent for the purposes of such federal and state statutes.

(b) Notwithstanding any law to the contrary, when the child is scheduled to reside an equal amount of time with both parents, the parents may agree to a designation as joint primary residential parents or to waive the designation of a primary residential parent. In the absence of an agreement between the parties, a single primary residential parent must be designated; provided, that this designation shall not affect either parent's rights and responsibilities under the parenting plan.