using Formula Field for Totaling or ??

I am trying to use a formula field on a form to total up 9 currency fields to generate a total that the user can see and then I can use to initiate a Payment. I can't seem to get it to accept all the fields? Is there a limit on the number of fields the formula filed will accept. Is there an easier way to do this with a currency field? I am new to Zoho and trying this out for the first time, so any help is appreciated. Thnaks