The Thrift Savings Plan (TSP) is a defined contribution plan for United States civil service employees and retirees as well as for members of the uniformed services. As of December 31, 2021, TSP has approximately 6.5million participants (of which approximately 3.9million are actively participating through payroll deductions), and more than $827.2billion in assets under management; it is the largest defined contribution plan in the world. The TSP is administered by the Federal Retirement Thrift Investment Board, an independent agency. The TSP is one of three components of the Federal Employees Retirement System (FERS; the others being the FERS annuity and Social Security) and is designed to closely resemble the dynamics of private sector 401(k) and Roth 401k plans (TSP implemented a Roth option in May 2012). It is also open to employees covered under the older Civil Service Retirement System (CSRS) but with far fewer benefits (mainly the lack of matching contributions). Eligibility Civil Service Retirement System (CSRS) employees may join at any time, but are not automatically enrolled. Service members in the Blended Retirement System (BRS) are automatically enrolled in the TSP at 5% of their base pay. Members of the military in the Legacy Retirement System may enroll in the TSP anytime but are not automatically enrolled. Federal Employees Retirement System (FERS) employees hired on or after October 1, 2020 are automatically enrolled upon hire, and 5% of base pay is automatically withheld unless the employee elects not to participate. Those hired between August 1, 2010 and September 30, 2020 (inclusive) were automatically enrolled upon hire with 3% of base pay withheld; employees hired on or before July 31, 2010 were not automatically enrolled and had to opt-in (initially after a waiting period of six months, this requirement was later dropped). Contributing and vesting An employee or uniformed service member may change, stop, or restart contributions, at any time, with very few exceptions noted below. Employee contributions As of October 1, 2020, new civilian employees and service members in the BRS are automatically enrolled in the TSP with a 5% deduction from their gross pay being deposited into the age-appropriate Lifecycle (L) Fund, unless they make another choice or choose not to participate. Employees hired before then either contribute automatically at 3% or do not have any automatic contributions and had/have to opt-in to TSP; their contribution levels did not change when the newer rules were implemented. All