You can make any text field in a form a calculated field. A calculated field will perform any of the following mathematical functions against other fields in your form (+,-, (),/,*).

To add an automatic calculation to a field, click on the field properties and enter a formula in the formula value. Basic math operations can be entered using form field IDs. You can also click once in the formula field value then click other fields on the form to automatically populate their form field ID in the formula value. The field will then turn orange to indicate it is a calculated field.

The following example demonstrates a formula for a total amount based on the values of the other form fields.

 For more tips on editing Form Fields go to Editing Form Fields.