cert-count.rb

class User
  has_one :plan
  has_many :certificates

  def remaining_certificates
    plan.available - certificates.current_month.count
  end

end

class Certificate
  belongs_to :user

  scope :current_month, -> {  where(:created_at => [Time.zone.now.beggining_of_moth, Time.zone.now.end_of_moth]) }

end

class Plan < User
  belongs_to :user


end