The Thrift Savings Plan (TSP) is a Federal Government-sponsored retirement savings and investment plan. It offers the same type of savings and tax benefits that many private corporations offer their employees under "401(k)" plans.

Blended Retirement System (BRS) Members of the Uniformed Services
If you are a member of the uniformed services who began serving on or after January 1, 2018, your service automatically enrolled you in the TSP (or will) once you had served 60 days and 3% of your basic pay is deducted from your paycheck each pay period and deposited in the traditional balance of your TSP account, unless you have made an election to change or stop your contributions. You can make an election by following the instructions in Starting, Changing, and Stopping Your Contributions.

Non-BRS Members of the Uniformed Services
If you are a member of the uniformed services who is not covered by the Blended Retirement System (BRS), your account is established by your service after you make a contribution election using your service's automated system, if it has one. For example, most members of the uniformed services use myPay. If your service does not use an electronic system, you can complete Form TSP-U-1, Election Form and return it to your service.

Reentering Members of the Uniformed Services

If you were already in the BRS plan before you left the service—whether as a new member of the uniformed services or an opt-in—you will be automatically reenrolled when you reenter. If you were not in BRS but had fewer than 12 years of service when you left, your service may give you the opportunity to opt in when you reenter. In either case, assuming you had served 60 days before leaving, your enrollment will begin with the first pay period after reentering. If neither situation applies to you, you can still start a TSP account or resume contributing to your existing account as a non-BRS member. Follow the instructions in Starting, Changing, and Stopping Your Contributions.