Difference between 2 dates in days

[Tehmina Aslam]

I have 2 fields Due date and Modified Due date. I want to get the difference between these two dates in days. 

I tried the following formula: 

{{[issue.Due date.diff(issue.Modified Due date).days}}

Then I tried even the Field ID:

{{[issue.Due date.diff(issue.customfield_10837).days}}

But that still does not work, The rule runs successfully but the field Lag time is never updated with value. 

[Vishal Biyani]

@Tehmina Aslam 

Can you copy the calculation in smart variable and then use that smart variable to update the issue? i think it should help resolve the issue.

Also there looks to be an extra [ bracket before Issue. That is not needed

Share your audit log as well

[Tehmina Aslam]

Thanks man, there was an extra bracket :D 

{{issue.Due date.diff(issue.modifiedDueDate).days}}