LTS ubuntu

Ubuntu 12.04 LTS 2012/?---------------------------------------------------------------2017/?
Ubuntu 10.04 LTS                                         2015/?

Ref>
https://wiki.ubuntu.com/LTS?action=AttachFile&do=get&target=ubuntu-release-cycle-2.png

A new LTS version is released every 2 years. In previous releases, a Long Term Support (LTS) version had 3 years support on Ubuntu (Desktop) and 5 years on Ubuntu Server. Starting with Ubuntu 12.04 LTS, both versions will receive 5 years support. There is no extra fee for the LTS version; we make our very best work available to everyone on the same free terms. Upgrades to new versions of Ubuntu are and always will be free of charge.