function calculate_age(birth_month,birth_day,birth_year) {
  today_date = new Date();
  today_year = today_date.getFullYear();
  today_month = today_date.getMonth();
  today_day = today_date.getDate();
  age = today_year - birth_year;

  if (today_month < (birth_month - 1))
    age--;
  if (((birth_month - 1) == today_month) && (today_day < birth_day))
    age--;
    
  return age;
}