JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
Are you referring to this form - http://www.jotformpro.com/form/43575646960971?
I made a clone of that form and tested the calculation. It seems to be working properly.
If you are referring to another form, can you please give us the link so we can investigate it further?