How to prepopulate date field in form to show current date + 30 days?

Is it possible to have a date field prepopulate showing the current date plus 30 days? 

Yes it is possible to achieve your requirement and here are the steps you need to follow:

#1. Add a "Date Picker" field in form and set it to display current day as default date. If you want you can hide this date field.

#2. Add another "Date Picker" field in form which you want to display to users.

#3. Add condition in form to check if the first date field is filled, insert +30 in the second date field. Please check the screenshot below:

Please check the following demo form I created for you and see if it works as expected:   https://form.jotform.com/80845335783970 

Feel free to clone this form for a closer look. The following guide should help you in form cloning:  https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL

Hope this helps.

Do get back to us if you have any questions.