Create Custom Entity Field that Displays the Difference Between Credit Limit and Balance

 
1. Navigate to Customization > Lists, Records, & Fields > Entity Fields > New.
2. Enter the name of the field on Label = Ex. Remaining Credit Limit
3. Set the Type = Currency
4. Set Store Value = F (not checked)
5. Under Applies To tab: Customer = T
6. Under Display tab, select Financial from the Subtab dropdown list
7. Under Validation & Defaulting tab, check Formula box then set this formula as Default Value:   ({creditlimit} - {balance})
8. Click Save or Save & Apply to Forms