How can I add a calculation to the configuration widget?

I believe you are pertaining to the Configurable List widget, is that correct?

I'm not sure how would you like to have the calculation to the Configurable List widget.

If you're trying to create a condition within the widget, from what I know, it is not possible.

The widget, however, can be affected by the conditions outside it. 

Can you help us understand your concern by giving us more details of what you would like to happen so we may check if there are any workarounds? We will wait for your response. Thank you. 

Thank you so much for the response. I would like the line cost= quantity*unit price
Sent on the new Sprint Network
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It is not possible to do a calculation within the Configurable List widget, you could work it in separate Text Box fields, and work along with the Form Calculation widget: http://widgets.jotform.com/widget/calculationv

https://www.jotform.com/help/259-How-to-perform-calculation-in-the-form

Another possible option would be working with the Spreadsheet widget: http://widgets.jotform.com/widget/spreadsheet

Let us know if you need more help, we will be glad to assist you.