private function calcFpl($personIncome, $persons, $period){
      $baseIncome   = 7820;
      $addPerPerson = 4320;
      $fplYearlyIncome = $baseIncome + ($persons * $addPerPerson);

      $weeksInYear   = 52;
      $biweeksInYear = 26;
      $monthsInYear  = 12;

      switch ($period){
        case "week":
          $personIncome = $personIncome * $weeksInYear;
          break;

        case "biweek":
          $personIncome = $personIncome * $biweeksInYear;
          break;

        case "month":
          $personIncome = $personIncome * $monthsInYear;
          break;
      }

      $fplPercent = ($personIncome / $fplYearlyIncome) * 100;
      return round($fplPercent, 2);
    }