You can use On2Air Formulas to live calculate data on a form.
Airtable Formulas do not live update on a form due to their API limitations, so you will need to add On2Air Formulas to calculate your data.
Here are some common calculations you can use that are similar to Airtable Formulas. They are based on EXCEL formulas.
CONCATENATE
To see the entire list of formulas available - https://formulajs.info/functions/