more than one instance of xenforo on the same domain

[DRE]

If i had xenforo on the root and xenforo on a subdomain, how much is that extra?

 

[Chris D]

One whole new license.

...single instance of the Software ("License") through a single installation. Each License may run one instance of the Software, accessible via one URL

 

[petertdavis]

I think it would also depend on why you're doing it. For example, if you had one license open to the public on your root, and another one that is just for testing on a password protected subdomain, I think you'd only need one license. If you're opening both up to the public, then I think Yorick is correct. For more complex situations I'd suggest opening a ticket with support and ask for clarification.