Custom Field: Get the Difference of Two Date Fields Using an SQL Expression

1. Navigate to Customization > Lists, Records, & Fields > Entity Fields > New

2. Create the Custom Fields

• Custom Field 1. 
  Label = Date Created
  ID = _datecreated
  Type = Date
  Store Value = T
  Applies To = Customer
  Display > Subtab = Main
• Custom Field 2.
  Label = Date Closed 
  ID = _dateclosed
  Type = Date
  Store Value = T
  Applies To = Customer
  Display > Subtab = Main
• Custom Field 3.
  Label = Days Open
  Type = Date
  Store Value = F
  Applies To = Customer
  Display > Subtab = Main
  Validation and Defaulting > Formula = T ; Formula field = ({custentity_dateclosed}-{custentity_datecreated})

3 . Pull up any Customer record > Fill out the custom fields. For example:

Date Created = 9/1/2012  
Date Closed = 9/3/2012 

4. Click Save.

5. Days Open field should show the value of 2.