Is the calculation widget available on starter package?

Yes, the Form Calculation widget is available under the Free plan. Please check this helpful guide: https://www.jotform.com/help/259-How-to-Perform-Form-Calculation-Using-a-Widget.

Actually, the only difference between the plans are the usage limits. It means that the Form Builder, Form Designer, Conditions, Apps and Widgets are available to all plans. Please check the pricing page for more details.

Hope that helps. If you have any questions, please let us know. Thank you.