Possible to Calculate Date 30 Days from Previously Submitted Date in Another Box?

[Nader Zargarpour]

Is that even possible, or would I have to have the user fill the 2nd box and put the "current date" (not necessarily "today") with the script then adding 30 days to that submitted date?

I was hoping I could use a prior box entry to calculate so as not to confuse the form user.