Your required minimum distributions (RMD's) begin in the year you turn 70 1/2, but that first RMD is not required to be satisfied in full until April 1 of the following year.  Make sure to complete that distribution by April 1, 2017.  Your future distributions are due at year end. 

Your IRA custodian or employer 401k plan can help you calculate that distribution.  You'll use the balance of your IRA or employer plan at December 31, 2015.