Why a $50,000 401(k) Roth Conversion Avoids Withholding, While the Same Move From an IRA Can Trigger a Tax Trap

Quick Read

• A 401(k) in-plan Roth conversion does not allow federal tax withholding, so the full $50,000 moves into the Roth and the tax bill shows up at filing time.

• An IRA conversion typically defaults to 10% withholding, which leaves only $45,000 in the Roth on a $50,000 conversion and can also create a $500 early-withdrawal penalty for anyone under 59½.

• Choosing zero withholding on Form W-4R and covering the tax with outside cash can help IRA owners avoid that problem and keep more money in the Roth.

When retirement savers move pre-tax money into a Roth, the big question is withholding. The answer depends on whether the money comes from a 401(k) or an IRA. The tax due on the conversion is the same either way, but the amount withheld in advance can make the April tax bill look very different.

Federal rules treat a transfer from a pre-tax account to a Roth IRA as income to the extent it would be taxable outside a qualified rollover. The 10% early distribution tax under section 72(t) does not apply to the converted amount. What differs is how the tax is collected and when it gets paid.

Where the Convertible Money Sits by Age

Federal Reserve Distributional Financial Accounts data show that these balances are concentrated among people nearing retirement. In the latest quarter, families ages 55 to 69 held about $8.5 trillion in defined contribution benefits. That represented 49.5% of families' total, while families ages 40 to 54 held another 33.1%.

Older households have also increased their share of these assets over time. People age 70 and older held 2.3% of these assets in 1989 Q3, and that figure rose to 9.4% in the latest quarter. The Fed data tracks defined contribution benefits by age, and the biggest pre-tax balances remain with families ages 55 to 69.

Why a 401(k) Conversion Comes With No Withholding

Inside an employer plan, the move from traditional to Roth is known as an in-plan Roth rollover. The IRS says there is no federal income tax withholding required on an in-plan Roth direct rollover, and it also says participants cannot elect voluntary withholding on these rollovers. If you convert $50,000 this way, the full amount goes into the designated Roth account.

The tax is then settled on the return. For the latest tax brackets discussed in the article, the 22% rate applies to single filers above $50,400, and the 24% rate begins above $105,700.

If the whole conversion falls into the 22% bracket, the federal tax would be $11,000. If it falls into the 24% bracket, the tax would be $12,000.

IRS Publication 575 says that if a rollover creates taxable income, taxpayers may need to raise withholding elsewhere or make estimated payments. In practice, that usually means using paychecks, outside cash, or quarterly estimated taxes to cover the bill.

How IRA Withholding Changes the Result

An IRA conversion is treated as a nonperiodic distribution. Federal law says the payer must withhold 10% unless the owner opts out. That election is made separately for each distribution, typically on Form W-4R. If no election is made on a $50,000 conversion, $5,000 is sent to the IRS and $45,000 lands in the Roth IRA.

That default withholding still does not cover the full tax. At a 22% rate, the liability would be $11,000, leaving $6,000 still due when the return is filed.

Side-by-Side Look at the Two Paths

What to Check Before Converting

IRA owners can avoid withholding by setting the withholding election to zero, which allows the full amount to convert while the tax is paid from cash outside the account. Anyone already past 59½ avoids the extra tax on withheld amounts, but any dollars withheld still permanently leave the Roth. Timing also matters, since the years between the last paycheck and the first required withdrawal can be a lower-tax window for a conversion.

Processing rules may still change. In Notice 2026-49, the Treasury Department and the IRS said they are considering guidance to standardize rollover procedures. One idea under review is a safe harbor allowing the distributing trustee to reasonably conclude that no withholding is needed on the rollover contribution. That discussion concerns rollovers between plans, while the 10% default for IRA-to-Roth conversions remains in the law.