Time of renewal license are summed or duplicate?

Hi, my client wants buy renewal license, and have a question. His license is still valid. When he buy renewal, and enter the license file to the program, the time of license are summed or duplicate?
e.g 30-10.2015 - this is time of original license
when he buy renewal today (27-09-2015), his license are valid to :
30-10-2016 or 27-09-2016?

It depends…
If you renew an existing license (within the renewal period) the remaining time should get added.
Else it’s handled as a new separate license.