Hi @sdnazdi
I hope you are doing well.
This isn’t possible out of the box, a suggestion is to replicate the form with the calculation and use the HTML field for that: https://wpmudev.com/docs/wpmu-dev-plugins/forminator/#html-field then you can use the macro {calculation-1} + hide the submit button using a visibility rule that will never match example calculation is 99999999, in case it is a “read only”
But, if you want to have a specific entry value from form ID 123 then you will need to code a custom it using the Forminator API get_entry and get_entries https://wpmudev.com/docs/api-plugin-development/forminator-api-docs/#method-get_entry
Best Regards
Patrick Freitas