If you have a traditional balance in your Thrift Savings Plan and want it sitting on the Roth side instead, the first thing to know is that the TSP will not do it for you. There is no button in your account that turns traditional dollars into Roth dollars. Many 401(k) plans offer an in-plan Roth conversion; the TSP does not.
That single fact reshapes the whole question. Converting your TSP to Roth means moving money out of the plan first, and the move triggers a tax bill in the year you make it. This article walks through what you actually can and cannot do, the one route that works, what it costs, and when the timing favors it.
The phrase gets used for two separate actions, and keeping them apart avoids most of the confusion.
The first is redirecting future contributions to the Roth TSP. The TSP has offered a Roth option since 2012, and you can change your contribution election so that new payroll money goes into the Roth balance instead of the traditional one. That is a contribution choice, not a conversion. It does nothing to the balance you have already built, and it is covered by the same logic as any Roth versus traditional decision: you are betting that your tax rate later will be higher than it is today.
The second is converting the traditional balance you already hold into Roth. That is what most people are after, and it is the one the TSP cannot do internally. You cannot convert traditional TSP to Roth TSP. You can only get the money to Roth by sending it somewhere the conversion is allowed, which means an outside Roth IRA.
An in-plan Roth conversion is a feature a plan has to choose to offer, and the TSP has not adopted it. So the traditional and Roth sides of your TSP stay in their own lanes for as long as the money is in the plan.
One related point catches federal employees off guard. Agency or service automatic and matching contributions always land in your traditional balance, even if every dollar you elect goes to the Roth TSP. The match is made with pre-tax money. So a committed Roth saver in the federal system still accumulates a traditional balance automatically, and that traditional money carries a future tax bill with it.
The core constraint: The TSP has no in-plan conversion. To move an existing traditional TSP balance to Roth, you roll it to a traditional IRA, then convert that IRA to a Roth IRA and pay the tax.
Getting traditional TSP money to Roth is a two-step sequence, and each step has its own rules.
Step one is a rollover. You move the traditional TSP balance into a traditional IRA. Done as a direct rollover, trustee to trustee, this is not a taxable event and nothing is withheld. The money simply changes custodians while keeping its pre-tax character. Avoid taking the money as a check to yourself, because an indirect rollover forces the TSP to withhold 20% and starts a 60-day clock to redeposit the full amount.
Step two is the conversion. Once the money is in a traditional IRA, you convert some or all of it to a Roth IRA. This step is taxable. The pre-tax amount you convert is added to your ordinary income for that year and taxed at your marginal rate.
The catch is eligibility for step one. You generally cannot move money out of the TSP while you are still working in covered federal service and under age 59½. The two common openings are separation from federal service, after which the whole balance is available to roll over, and reaching age 59½, at which point the TSP allows in-service withdrawals you can roll to an IRA. Until one of those doors opens, the traditional balance stays put.
The tax is the entire decision, so it is worth seeing the math on real numbers rather than in the abstract. A conversion does not cost a penalty (the 10% early-withdrawal penalty does not apply to a conversion), but it does add fully to your taxable income.
Take employee A, who separated from federal service at 58 with $400,000 in traditional TSP, now rolled into a traditional IRA. Suppose this year their other taxable income is low, and they have room in the 12% and 22% brackets before reaching the top of the 24% bracket. They convert $80,000. That $80,000 stacks on top of their other income and is taxed as ordinary income. If it all falls in the 22% bracket, the conversion costs about $17,600 in federal tax, plus any state tax. After paying, that $80,000 is Roth money: it grows tax-free and comes out tax-free in retirement.
One rule matters more than any other here. Pay the conversion tax from money outside the retirement account, such as a taxable brokerage account or cash. If you instead have tax withheld from the converted amount itself, that withheld portion never reaches the Roth, and if you are under 59½ it counts as an early withdrawal subject to the 10% penalty. A conversion works best when every converted dollar lands in the Roth and the tax is covered separately.
Because the cost is locked to your tax rate in the year you convert, the goal is to convert in years when that rate is low. For many federal retirees, the lowest-rate years are the stretch between leaving service and the start of a FERS pension in full, Social Security, and required minimum distributions. Income dips, the brackets have room, and converting then fills the low brackets with money you control.
Converting the whole balance in one year usually backfires, since a large conversion pushes the later dollars into higher brackets and can raise the share of any Social Security that gets taxed. Spreading the conversion across several low-income years keeps each year's converted amount inside the brackets you are willing to pay. The same low-bracket window is the one our guide on how Social Security is taxed describes, and conversions interact with it directly, so the two decisions are best made together.
There is also a longer-term reason to move traditional money to Roth: required minimum distributions. A traditional TSP, and a traditional IRA, force taxable withdrawals starting at age 73 whether you need the money or not. A Roth IRA has no required distributions during your lifetime. Converting earlier, in low-income years, shrinks the future balance that would otherwise generate forced taxable income later.
Each Roth conversion starts its own five-year clock. If you are under 59½, the converted amount has to stay in the Roth IRA for five years before you can withdraw that converted principal without a 10% penalty. Past 59½, the penalty side falls away, though a separate five-year rule still governs whether the account's earnings come out tax-free. For someone converting in their late 50s or 60s and planning to leave the money invested for years, neither clock is usually a problem, but it is a reason not to convert money you expect to spend within five years.
If your aim is simply to have more Roth money going forward and you are still working, the simplest path is to change your contribution election to the Roth TSP. No tax event, no rollover, and your money keeps the TSP's low costs. The table below sorts the options by what you are actually trying to do.
| Your goal | What to do | Tax now? |
|---|---|---|
| Put future contributions in Roth | Change your election to Roth TSP | No (contributions are after-tax) |
| Move an existing traditional balance to Roth | Roll to a traditional IRA, then convert to a Roth IRA | Yes, on the converted amount |
| Move an existing Roth TSP balance out | Roll directly to a Roth IRA | No (already Roth) |
Rolling the Roth TSP itself to a Roth IRA is worth a mention, because it is not a conversion at all and carries no tax. It can still be useful: a Roth IRA has no lifetime required distributions and a wider investment menu than the TSP's funds, while the TSP keeps costs very low. That trade is about features and fees, not about a tax bet.
You cannot flip a traditional TSP balance to Roth inside the plan, and no contribution election changes the money you have already saved. The one route that moves an existing balance to Roth is a direct rollover to a traditional IRA followed by a Roth conversion, and the tax on the converted amount is the whole cost of the decision. Convert in low-income years, in amounts that stay inside brackets you accept, and pay the tax from outside funds.
Whether a given conversion schedule leaves you better off depends on your future tax rates, your other income, and how long the money keeps growing, which is more than a single year's math can show. Enter your balances, your retirement age, and your spending, and run the simulation to see how shifting traditional dollars to Roth, year by year, changes how long the money lasts and what you owe along the way.
Enter your traditional and Roth balances, your retirement age, and your spending, then run a Monte Carlo simulation to see how a conversion strategy plays out under a tax-aware drawdown.
Run the Calculator →