To do set your company's appraisal frequency, go to the Reminders tab of your Company Settings. Scroll down the page until you come to 'Appraisals' and enter your appraisal frequency in months.

Once the first appraisal has been set for a staff member, the system will set their next appraisal due date, which will prompt a reminder to managers and admins closer to the time.

NB: This is a company-wide rule and you cannot set different appraisal frequencies.