The Internal Revenue Code (IRC) requires that you begin receiving annual distributions from your beneficiary participant account according to its required minimum distribution rules. These rules require you to receive a certain portion of your account each year based on your life expectancy.
The required minimum distribution rules apply to your TSP account as a whole. The calculation of your RMD takes into account both traditional and Roth balances.
The date on which you must begin receiving required minimum distributions (RMDs) depends on whether the deceased participant died before or on/after his or her "required beginning date." The required beginning date is defined as April 1 of the year following the year a participant reaches age 70½, or separates from government service, whichever is later.
For example, if a separated participant was born on June 1, 1945, he or she would turn age 70½ on December 1, 2015; and his or her required beginning date would be April 1, 2016.
Because the rules are complex, more specific information about the IRS required minimum distribution rules can be found in the TSP tax notice "Tax Information About TSP Withdrawals and Required Minimum Distributions for Beneficiary Participants."
You may not request a payment of your RMD because that is not one of the statutory TSP withdrawal options. However, if you chose monthly payments based on life expectancy, the total dollar amount of your annual payment will approximate your RMD.