Workflow update a field based on another field

Workflow update a field based on another field

Hi there,

I am trying to set a workflow to cater for the following scenario.
I have 3 fields in one of my form layouts:

Start Date
Active Period
End Date

I want to set a workflow so that on Start Date/Active Period edited, to set the End Date to Start Date + X days, but it seems currently not possible and you can only set a Date field to a specific value or an execution date?