Hi @signalwarrant
If you need to save the total in the database, then I believe you can use the acf_form() function. Please check these pages to learn how to use it: https://www.advancedcustomfields.com/resources/create-a-front-end-form/, https://www.advancedcustomfields.com/resources/using-acf_form-to-create-a-new-post/.
You can also do the calculation in the acf/save_post action hook and use the update_field() function if you want to save it in a custom field.
I hope this helps 🙂
