A 61-year-old GS-15 earning $180,000 can funnel over $34,000 of her own pay into the TSP in a single calendar year — and her agency adds another $9,000 on top. At a 7% return over four more working years, that final push alone grows to roughly $190,000 before she takes her first required distribution. The TSP is not a side benefit.

For most FERS employees, it is the largest pool of liquid retirement wealth they will ever accumulate, and the rules governing how much goes in, how it grows, and when it must come out changed substantially under SECURE 2.0. Getting the contribution limits, fund mechanics, and RMD age wrong costs real money — and costs exam points.

The TSP operates like a 401(k) in structure: the employee elects a percentage of each paycheck to defer into the plan, picks from a menu of investment funds, and the money grows tax-deferred (or tax-free in a Roth TSP) until withdrawal.