Humanised keeps track of joined dates and resigned dates of all employees for a number of different reasons including pro rata calculations. When you create a payrun for a certain pay cycle (month) Humanised will look for any employees who have joined or left in the middle of the pay cycle.
Depending on whether you consider the number of days in the calendar month, a fixed number of days or variable number of days, it will calculate the number of days the employee has worked and prorate the salary accordingly.
However, we realize that prorated salaries are not that straightforward. For this reason, you can further adjust your no.of days worked for the month. This will recalculate the pay categories you have selected in company settings in real time.