Dana spent eleven years at a software company before taking a federal job at 41. She left behind a 401(k) worth about $142,000 and had a rollover IRA of $38,000 from an even earlier job. Two years into her federal career, she opened a statement from the old plan and noticed the fund fees: 0.85% on her main holding. On $180,000 combined, that is roughly $1,530 a year. Her TSP index funds, by comparison, charge a few hundredths of a percent.

She asked a simple question: can I just move all of this into the TSP?

Often, yes. Whether you should is a more interesting question.

What the TSP will and won't accept

The TSP takes transfers from several kinds of accounts, but not all of them.

Accepted:

  • Traditional IRAs
  • Eligible employer plans, including 401(k), 403(b), and governmental 457(b) plans
  • SEP and SIMPLE IRAs (SIMPLE IRAs only after the two-year participation period)
  • Roth balances from eligible employer plans (a Roth 401(k), for example), which land in your Roth TSP balance

Not accepted:

  • Roth IRAs
  • After-tax (non-Roth) money, including nondeductible IRA contributions

That last point trips people up. If your traditional IRA holds a mix of pre-tax and after-tax dollars, the TSP will only take the pre-tax portion, and the rules for splitting it are not always intuitive. The IRS Form 8606 tracks your basis, so have that in front of you before you start.

You also need an existing TSP account. Both current and separated participants can transfer money in, but the rules and forms occasionally change, so confirm the details at tsp.gov before you start.

Why moving money into the TSP can make sense

Lower costs

Fees compound quietly. Say you move $180,000 from funds charging 0.85% into TSP funds charging around 0.05%. That is a savings near $1,440 a year, and the gap grows as the balance does. Expense ratios shift every year, so check the current figures at tsp.gov rather than trusting any number printed in an article, including this one.

The pro-rata rule goes away

This is the sleeper benefit for higher earners. If you want to do a backdoor Roth IRA contribution, the IRS looks at all of your pre-tax IRA money when you convert, not just the dollars you put in that year. A $90,000 pre-tax IRA balance can make a clean backdoor conversion mostly taxable.

Move that pre-tax IRA into the TSP and it is no longer counted as IRA money. Your backdoor Roth can go back to being simple. Employer plan balances are not part of the pro-rata calculation, which is the whole point.

Penalty-free access in your mid-50s

If you separate from federal service in or after the year you turn 55, TSP withdrawals avoid the 10% early withdrawal penalty. (Special categories like certain public safety employees have different ages.) Regular IRAs do not get this treatment. Money you move into the TSP generally takes on the TSP's rules, though you should verify the specifics for your situation.

For someone planning to retire at 56, this can matter more than any fee comparison. You pay ordinary income tax on traditional withdrawals, but not the extra 10%.

Simplicity and creditor protection

One account is easier to manage than four. TSP balances also carry strong federal protections, though the details differ from state to state for IRAs, and an attorney can tell you more if this is a concern.

When it may be the wrong move

The TSP is a tidy, low-cost menu, not an all-purpose investment platform. You get the G, F, C, S, I, and L Funds. That is it.

Think twice if:

  • You want choices the TSP does not offer. Individual stocks, real estate funds, bond ladders, annuity products, or small-cap value tilts are all out of reach inside the TSP.
  • You rely on flexible withdrawals. The TSP has improved its withdrawal options in recent years, but IRAs still let you take money out in whatever amounts and on whatever schedule you like, with fewer account-level restrictions. If you are planning a staged Roth conversion strategy in retirement, check what the TSP currently allows in terms of in-plan conversions. That area has been changing.
  • You expect to need the money before 55. Rolling a traditional IRA into the TSP does not create penalty-free access earlier than the TSP's own rules. Your IRA could, in some cases, offer exceptions like substantially equal periodic payments that you would want to keep available.
  • You are not sure you will stay in the system. A transfer from the TSP back out to an IRA is possible after you separate, but it adds steps.

How the transfer actually works

You will use the TSP's transfer-in form (currently Form TSP-60, but check tsp.gov for the current version). The process looks like this:

  1. Get the details from your old plan or IRA custodian. You need the account number, the custodian's address, and instructions for a direct transfer.
  2. Complete the TSP form. You will specify the amount and whether it is traditional or Roth money.
  3. Have the old custodian sign or process their portion, depending on the institution.
  4. The custodian sends a check payable to the TSP, or in some cases a wire.
  5. The money is invested according to your current contribution allocation unless you change it.

That last step matters. If you are 100% in the C Fund for new contributions, a $180,000 transfer goes into the C Fund too. If that is not what you intended, rebalance with an interfund transfer after the money lands.

Ask for a direct rollover, meaning a check payable to the TSP, not to you. If a check is made out to you personally, you generally have 60 days to deposit it, and a 401(k) distribution paid to you may have 20% withheld for taxes. You would then have to replace that withheld amount from other funds to roll over the full balance. It is a hassle you can skip.

A quick example with real numbers

Marcus is 47 and earns $165,000 as a federal contractor turned employee. He has a $70,000 traditional IRA and wants to make a backdoor Roth contribution of $7,000 each year (limits change annually, so check irs.gov).

With $70,000 pre-tax in the IRA, nearly all of any conversion is taxable under the pro-rata rule. Roughly 91% of a $7,000 conversion ($70,000 divided by $77,000 total) would be taxable, even though he only just contributed after-tax dollars.

If he moves the $70,000 into the TSP first, his IRA balance drops to zero by year-end. The conversion becomes basically tax-free. And his TSP fees drop on the $70,000 too.

Timing matters here. The pro-rata calculation uses your IRA balances as of December 31 of the conversion year, so get the transfer completed before then.

The decision in plain terms

Move the money if you want lower costs, simplicity, a cleaner backdoor Roth path, or access under the age-55 separation rule. Keep it where it is if you value investment variety or have a specific plan that depends on IRA features.

Many people do both: they move the pre-tax IRA into the TSP and leave a Roth IRA alone, since the TSP cannot accept it anyway.

Before you submit anything, confirm current rules at tsp.gov, pull your latest Form 8606 if you have after-tax IRA money, and talk with a tax professional if your situation involves a mix of Roth, pre-tax, and after-tax balances. A rollover is easy to start and fussy to undo.