Before completing the necessary forms to purchase your annuity, you should read the TSP booklet Withdrawing Your TSP Account After Leaving Federal Service.
If you have determined that an annuity is appropriate for your needs, you should complete Form TSP-70, Request for Full Withdrawal. Be sure to read the form and instructions carefully as they outline specific requirements that must be met in order to avoid any unnecessary delays in processing. Keep in mind that there is a $3,500 minimum amount required to purchase an annuity. If you are using only a portion of your account for an annuity, the percentage of your account that you choose when requesting it must equal $3,500 or more of your vested account balance.
After the TSP receives all of the information and documentation necessary to purchase your annuity, it may take up to several weeks to process your request and disburse your funds.
Your annuity will be purchased from the TSP annuity provider. The annuity provider is competitively chosen by the Federal Retirement Thrift Investment Board, the agency that administers the TSP.
Once the money has left your account, you should direct all communications concerning your annuity to the annuity provider. The provider will send you a package of information and an annuity contract. Your monthly annuity payments will begin approximately one month after the annuity is purchased.