How to calculate a totals field in a form with 20 currency input fields?

If you have a form generated by Wappler that has, say, 50 fields and 20 of those are currency input fields that are auto populated depending on selections made by the user, what is the best way to calculate a total and put it in a Totals field ready for inserting into a DB?

I know it is a fairly generic question but was wondering before I build a page.