Custom forms enable you to gather information from users that standard Outlook forms don't include, and they allow you to reorganize the standard form fields in ways that make more sense to your users. For example, you might use a custom form in a public folder to receive support requests from users.
Outlook provides a relatively rich set of tools for creating forms and for adding special fields to the forms. For example, to add formula fields to a form to calculate tax or other information, follow these steps:
In addition to using custom fields in a form, you can also use the default form fields—including text fields—as applicable in a formula field. Outlook provides several functions you can use in the formula for math, date and time, and other types of calculations.