A: Prorated rent is the cost of rent per day. It's used to determine the amount of rent due from tenants who will not be occupying a property for a full month. Regardless of the number of days in the month, to calculate prorated rent, always divide the month's rent by 30.Then multiple this amount by the number of days a tenant is responsible for the rent.t's used to determine the amount of rent due from tenants who will not be occupying a property for a full month. Regardless of the number of days in the month, to calculate prorated rent, always divide the month's rent by 30.