How Compliance percentage is calculated?

Here is the calculation of Compliance percentage:

Numerator: (Y+Z)
Denominator: (X+Y+Z)

Where:
X: total number of activities assigned to the user with status overdue (irrespective of the assignment or due date)
Y: total number of activities assigned to the user with status pending (irrespective of the assignment or due date)
Z: total number of activities completed by the user in the last 18 months (irrespective of when they were assigned but they were completed in last 18 months)

Status definition:-
Overdue
Pending
Completed