What is a reasonable review period when setting targets for an employee who is underperforming?

There is no statutory time frame for improvements for underperformance. Timescales for an employee's improvement must be reasonable and will depend on the circumstances, including the employee's role and position with the employer and their length of service and past performance. In some cases, a review period of a few weeks may be sufficient. In others, a review period of several months may be more appropriate. Where an employer agrees to provide an employee with additional training or support, this will need to take place before the employee's performance can sensibly be measured again. The employer should ensure that it monitors the employee's performance during the relevant review period. The period should be long enough to enable the employer to assess whether or not the employee has made and sustained the necessary improvements.