Should we be inputting an employee's salary 'effective date' as the last time they got an increase, or the date when they are scheduled for the next upcoming increase?

In KC detailed budget, enter the salary effective date as the date of the last effective increase, and not as the date of the next scheduled increase.  
 
As an example, if listing a graduate student in your detailed budget with effective dates 7/1/25-6/30/26, and you know the student's salary from June 2024, enter that amount with salary effective date of 6/1/24.  KC will then appropriately calculate the costs for the period 7/1/25-6/30/26 taking into account the increase that will take effect 6/1/25 for the grad student.
 
For information on when different salaries inflate, please see KC Default Salary Inflation by Month and Category.