How can I send calculation field data from one form to another?

Unfortunately widgets cannot be pre-populated and this is because they work in a different way compared to standard fields (Text Box, Radio Buttons, Check Boxes, etc ).

But there is a workaround for this, you will need to add a field to the first form, the one where you want to capture the data:

Then once the field is added you will need to add a condition, so if the the calculation widget is filled its value will be copied to the field you will add, it is a text box. 

Now you will get the value of the text box you added and this will be passed through the URL, then in the second form, where you will receive the value you will not use conditions, but you will need to add always a text field that will receive the value passed via the URL, and once this is added you will add it to the calculation widget too: 

So with this workaround you will be able to pass the value from a calculation widget to another one. 

Please if you have questions, do let us know, we will be glad to help.