What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
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.
Inside of this guide you can find how to pass field value to another field:
If you want to have hidden field on your form you can use Hidden Box widget.
Or you can use Text box field and set Hide field option to ON, inside of field Properties > Advanced tab.
You can also use Form calculation widget. With this field you can perform calculation and you can also hide it.
Hope this will help. Let us know if you need further assonance.