What is the maximum number of form fields before upgrade is required?

I am assuming by "form fields" limit you meant form submissions as we do not have limits to the number of fields you can have in a form. The maximum number of form submissions for free accounts is 500 submissions. Once you have exceeded the form submissions limit you will be required to upgrade to either Bronze, Silver or Gold

https://www.jotform.com/pricing

Hope this information was helpful. Thank you