401k to Roth IRA Tax Implications

Previously untaxed 401(k) money that is rolled into a Roth IRA is generally included in gross income in the year of the rollover. That commonly includes pre-tax employee deferrals, employer contributions, and tax-deferred earnings. The receiving Roth IRA does not create a deduction that offsets this income. [1] [2]

A plan may also contain designated Roth contributions, valid after-tax non-Roth employee contributions, or several money sources at once. Valid after-tax contribution principal generally should not be taxed a second time, although associated earnings are generally pre-tax. Designated Roth money has its own qualified-distribution and rollover rules. The plan’s records—not the account’s total market value alone—are needed to identify the taxable portion. [2] [3]

Need to identify which 401(k) transactions may be available first? Read Can I Transfer My 401(k) to a Roth IRA? before modeling the downstream tax implications.

Federal income-tax brackets are marginal. Added taxable conversion income fills the next available layers of taxable income; entering a higher bracket does not cause every earlier dollar to be taxed at that higher rate. The relevant starting point is projected taxable income before the rollover—not salary, adjusted gross income, or the 401(k) balance by itself. [4]

For 2026, the 22% bracket for married couples filing jointly ends at $211,400 of taxable income, and the 24% bracket begins above that amount. For single filers, the 24% bracket begins above $105,700. Those figures are taxable-income thresholds after applicable deductions, not gross-income cutoffs. [4]

This marginal-bracket illustration assumes the full $60,000 is pre-tax and excludes state tax, credits, deductions, Social Security, Medicare, Marketplace coverage, and other return items. A complete return may differ.

When a plan sends an eligible distribution directly to a Roth IRA, the direct rollover generally is not subject to mandatory withholding. That may help keep the full intended amount inside the retirement system, but it also means no federal tax may have been prepaid for the taxable income created by the transaction. [1]

When a taxable eligible rollover distribution is paid to the participant instead, the plan generally must withhold 20% for federal income tax. To roll over the entire distribution within the applicable period, the participant generally needs to replace the withheld amount with other funds. Any amount not rolled over may be taxable and may also face an additional tax depending on the facts. [1]

A properly completed rollover can be taxable without being subject to the separate 10% additional tax. IRS Publication 575 states that the 10% additional tax does not apply to the amount rolled over, even when untaxed qualified-plan money is rolled into a Roth IRA and included in gross income. [2]

That distinction can be lost when people use “tax” and “penalty” interchangeably. An amount paid to the participant and not rolled over may receive different treatment. Later Roth IRA withdrawals also follow separate ordering, five-year, age, and exception rules. The validity of the rollover and the treatment of a later withdrawal are different events.

For the narrower additional-tax question, see 401(k) to Roth IRA Without Penalty: 2026 Rules.

State treatment does not always mirror the federal result. A state may tax the conversion, exclude some retirement income, use a different definition of taxable income, or provide age-based deductions or credits. Local income tax can also matter in some places.

Residence, part-year residency, an anticipated move, and state conformity rules may affect the comparison. Review the state return and residency facts instead of treating the federal illustration as the full cost.

For households receiving Social Security, additional conversion income can increase the portion of benefits included in taxable income. The federal calculation generally uses one-half of Social Security benefits plus other income and tax-exempt interest. Depending on the starting point, added rollover income may cause more of the benefit to become taxable. [5]

“Up to 85% of benefits may be taxable” does not mean Social Security is taxed at an 85% rate. It means up to 85% of benefits may be included in taxable income, which is then subject to the household’s applicable marginal rates. A simplified bracket-only estimate can miss this interaction.

See the dedicated guide to Roth conversions and Social Security taxation for the combined-income framework.

Medicare may add income-related monthly adjustment amounts—IRMAA—to Part B and Part D premiums when modified adjusted gross income exceeds applicable thresholds. Social Security generally uses tax-return information from two years earlier, so a 2026 conversion may affect a later premium year rather than the month in which the rollover occurs. [6] [7]

IRMAA works through threshold bands. Crossing a threshold can change monthly premiums for the covered person, and married households may have two Medicare enrollees. The actual effect depends on filing status, the tax year used, later premium-year rules, and whether a qualifying life-changing event supports a new determination.

Review the current framework in Can a Roth Conversion Increase Medicare Premiums? and use the educational tax-bracket and IRMAA calculator for a first-pass comparison.

For people not yet on Medicare who buy coverage through the Health Insurance Marketplace, premium assistance is generally based on expected household modified adjusted gross income for the coverage year. Taxable rollover income may increase that income and change the Premium Tax Credit. The credit is reconciled on the federal return using actual annual information. [8] [9]

Marketplace assistance generally looks at the current coverage year, while Medicare usually looks back two tax years. A household approaching Medicare may need to model both timelines.

The separate guide on Roth conversions and the ACA Premium Tax Credit explains this same-year interaction in more detail.

The transaction is generally included on the return for the calendar year in which the rollover occurs. But the tax system is pay-as-you-go. Depending on withholding, estimated payments, other income, and prior-year tax, waiting until the filing deadline to make every payment could create an underpayment penalty even when the return itself is filed on time. IRS Publication 505 explains withholding and estimated-tax rules. [10]

For payment dates, withholding choices, and safe-harbor context, read When Are Taxes Due on a Roth Conversion?.

The distributing plan generally reports the transaction on Form 1099-R. IRS instructions describe reporting the gross distribution in box 1, the taxable amount in box 2a when determinable, and employee contributions or designated Roth basis in box 5 where applicable. The receiving Roth IRA generally reports rollover contributions on Form 5498. [3]

Forms can arrive at different times. Retain the plan statement, rollover confirmation, Forms 1099-R and 5498, basis records, and tax return together.

1. Does the plan currently permit a distribution or direct rollover?
2. How much of the eligible balance is pre-tax, designated Roth, after-tax contribution basis, and earnings?
3. What is projected taxable income before the rollover?
4. Which marginal federal brackets would different rollover amounts enter?
5. How might state and local income taxes change the estimate?
6. Could the added income increase taxable Social Security benefits?
7. Could it cross a Medicare IRMAA threshold two years later?
8. Could it affect a current-year Marketplace Premium Tax Credit?
9. Would capital gains, credits, deductions, or net investment income create other interactions?
10. How would the household make timely tax payments if a direct rollover has no withholding?
11. Could an amount not rolled over face the 10% additional tax?
12. Do the plan administrator and receiving custodian have matching instructions?
13. Which records will establish the amount received and any basis?
14. How do the current tax cost and future retirement-income assumptions compare?

• Previously untaxed 401(k) money moved to a Roth IRA is generally included in gross income.
• A valid rollover may avoid the 10% additional tax without avoiding ordinary income tax.
• A direct rollover generally avoids mandatory 20% withholding, which can leave a separate tax-payment need.
• Federal brackets are marginal, and the complete return determines the incremental tax.
• Social Security taxation, Medicare IRMAA, Marketplace credits, and state tax may change the result.
• Forms 1099-R, 5498, plan records, and receiving-account records should be reconciled.
• Comparing several educational scenarios can clarify which assumptions deserve professional review.