How does that work?

The value of each day of holiday is then fixed for the holiday year (1 April to 31 March). So the cost of buying or selling holiday will not change if your salary changes during the holiday year. For example, if you start working part-time after buying or selling holiday as a full-time employee, the number of days and the monthly cost will not be adjusted. At the next annual enrolment, the value of each hour/day of holiday will be recalculated based on your new salary.