Here is the release schedule for Ubuntu 16.04 LTS. Please note that this is a preliminary Schedule.
December 31st Alpha 1 (for opt-in flavors)
January 28th Alpha 2 (for opt-in flavors)
February 25th Beta 1 Freeze (Monday), Beta 1 (for opt-in flavors)
March 24th Final Beta
April 21st FinalRelease Ubuntu Ubuntu 16.04
For the complete release schedule: Xenial Xerus release schedule