Required Minimum Distributions (RMDs) generally are minimum amounts that a retirement plan account owner must withdraw annually starting with the year that he or she reaches 72. The annual deadline for taking your RMDs is December 31. However, it's possible to delay taking your first RMD until April 1 of the following year you turn 72.
Generally, an RMD is calculated for each account by dividing the prior December 31 balance of that IRA or retirement plan account by a life expectancy factor that the IRS publishes in Tables in Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs). Choose the life expectancy table to use based on your situation.