Average between two colums containing dates

[AMonot]

Ahoy ! 

I am trying to create a KPI which would display a single number. 

This number should be the average time that passes between two main steps, from the "Booked Date" to "Initialization Date" (in days).

Basically I have two colums, each containing a date for each row. What I need is: 

• Calculate the difference between the "Initialisation Date" and the "Booked Date" for each row (in days)
• Calculate the average of all the results

The tricky part is that sometimes, I do not have an "Initialisation Date", and in this case, I want my formula to disregard this row. 

I would like to present it in a KPI indicator, but I cannot seem to find the correct formula to put in.

I am so sorry for my medium English level, hope I am understandable though... 

Thanks in advance ! 

A.M.

[Taoufiq_Zarra]

@AMonot  can you share a sample and the expected output ?

[AMonot]

Hey Taoufiq, 

Thank you for your answer. 

The output expected is a KPI, a single number displayed with a title. 

Here is an example of what I want on Excel : 

The "AVERAGE" number in orange (D10) is what I want displayed in my KPI on QlikSense. 

As you can see, there is two dates for each customer: one "Booked Date" and one "Initialization Date". I simply want to calculate the difference between those two and have the average of all the results. But I also want the formula to disregard the customers where the Initialization date is empty (like Zineya in C5) and only calculate the average on rows where there are all the data.