Is the TSP a 401(k)? What's the Same, What's Different

Last Updated: August 9, 2026 Reading Time: 7 min

The Legal Difference, in One Paragraph

A 401(k) is a private-employer arrangement under section 401(k) of the tax code. The TSP was created by the Federal Employees' Retirement System Act of 1986 (5 U.S.C. 8351 and 8401-8479), and section 8440 directs that its fund be treated as a 401(a) qualified trust, the same family as pension trusts. That's why the honest answer to "is TSP a 401(k)?" is no, while the honest answer to "will it behave like my old 401(k)?" is almost always yes. ERISA, the law governing private plans, doesn't apply; the Federal Retirement Thrift Investment Board and Title 5 govern instead.

FedTools 2026 comparison, verified against tsp.gov and IRS Notice 2025-67.

Where the TSP Simply Wins

Fees. At roughly 0.036% for the core funds, a $200,000 TSP balance pays about $72 a year in fund expenses. The same balance in an average 401(k) lineup pays over $1,000. Across a career, that difference compounds into tens of thousands of dollars, which is why rolling an old 401(k) into the TSP is often smarter than the reverse. Our TSP fee advantage analysis runs the long-term numbers.

The G Fund. It earns the weighted average yield of all outstanding Treasury notes and bonds with four-plus years to maturity, while its price never drops. Private plans can't offer it because the underlying securities are special-issue federal instruments available only to the TSP. It's the only place a retail investor gets long-term Treasury yields with zero market-price risk.

The match. FERS employees get 1% automatic plus up to 4% matching: a guaranteed 5% of salary for contributing 5%. Plenty of private plans match as well or better, but plenty match nothing at all.

Where a 401(k) Can Beat the TSP

Menu breadth, mostly. A good private plan may offer dozens of funds, brokerage windows with cheap access, and faster plan features. The TSP's answer, the Mutual Fund Window, opens about 4,500-5,000 outside funds but charges $132 a year in flat fees plus $28.75 per trade and requires a $40,000 minimum balance, economics that only make sense for larger balances with a specific need.

Withdrawal mechanics also run more rigid in TSP than in flexible private plans, and FERS spousal-consent rules add a signature requirement most 401(k) participants never encounter.

The Two-Jobs Question

Plenty of feds moonlight, and plenty of new feds arrive mid-year from private jobs. The rule: one elective deferral limit across all plans. Contribute $15,000 to a private 401(k) by June and you have $9,500 of TSP room left for the year, not a fresh $24,500. The $72,000 total-additions cap, which counts employer money, applies separately per unrelated employer, which is why maxing both matches is still worthwhile.

When to Roll In, When to Roll Out

The rollover question comes up at both ends of a federal career, and the answer usually follows the fees.

New feds with an old 401(k): rolling it into the TSP is often the quiet win. The money lands in funds costing ~0.036 percent instead of a private lineup averaging fourteen times that, and it consolidates your retirement picture into one statement. The trade-off is menu: if your old plan held a specific fund you love, the TSP's five core funds won't replicate it. Check one thing first: only pre-tax and Roth employer-plan money rolls in cleanly; Roth IRA balances cannot be rolled into the TSP at all.

Departing feds: the pull toward an IRA is flexibility (any fund, any withdrawal schedule, easier beneficiary handling), and for many people that's worth it. But two TSP features argue for leaving at least some money behind: the G Fund, which you lose forever once the balance leaves, and the age-55 separation exception, which lets someone who separates in or after the year they turn 55 withdraw penalty-free from the TSP years before an IRA would allow it at 59½. A split, part stays for the G Fund and early access, part rolls out for flexibility, is a legitimate answer.

One mistake to avoid in either direction: an indirect rollover, where the check comes to you, triggers 20 percent withholding and a 60-day deadline. Direct trustee-to-trustee transfers avoid both.

Model Your TSP Like the Account It Actually Is

Whatever the legal wrapper, the balance follows the same math as any retirement account. The free TSP Calculator projects your balance to any retirement date, the TSP Loan Calculator prices a loan against lost growth, and our milestone benchmarks by age show whether you're on track.

Frequently Asked Questions

Is the TSP a 401(k)?

No. It's a 401(a) governmental trust created by FERSA. It functions like a 401(k) for contributions, matching, loans, and rollovers.

Do TSP and 401(k) contributions share one limit?

Yes, one combined $24,500 ceiling in 2026 across all your elective deferrals, plus your applicable catch-up.

Can I roll money between TSP and a 401(k)?

Both directions, traditional-to-traditional and Roth-to-Roth. Rolling old 401(k) money into TSP captures the low fees.

What does TSP have that no 401(k) does?

The G Fund and near-zero expense ratios. No private plan can replicate the G Fund's structure.

What are the 2026 limits?

$24,500 elective deferral; $8,000 catch-up (50-59 and 64+); $11,250 super catch-up (60-63); $72,000 total additions.

Is the TSP covered by ERISA?

No, it's a governmental plan under Title 5 with FRTIB oversight.

Related Resources

• TSP vs Private 401(k): The Fee Advantage: What 0.036% vs 0.52% costs over a career
• Roth vs Traditional TSP: Which side of the TSP to fill first
• TSP Milestones by Age: Benchmarks for where your balance should be
• TSP Calculator: Project your balance to retirement

Sources: TSP.gov, IRS Notice 2025-67 (2026 limits), 5 U.S.C. 8351, 8401-8479, 8440, FRTIB.