Rolling over a traditional 401(k) to a Roth IRA gives you tax-free withdrawals in retirement, eliminates required minimum distributions during your lifetime, and can reduce the tax burden your heirs face when they inherit the account. The tradeoff is straightforward: you pay income tax on the converted amount now in exchange for never paying tax on that money again. Whether that tradeoff works in your favor depends on your current income, your expected tax rate in retirement, and how long the money has to grow.
Tax-Free Withdrawals in Retirement
A traditional 401(k) is funded with pretax dollars, so every dollar you withdraw in retirement gets taxed as ordinary income. A Roth IRA flips that arrangement. You pay tax on the money going in (or in this case, on the amount you convert), and then withdrawals in retirement come out completely tax-free, including all the investment growth.
This matters most if you expect your tax rate to be higher in retirement than it is today. That can happen for several reasons: future tax legislation could push rates up, your retirement income from Social Security, pensions, or other accounts could land you in a higher bracket, or you might simply have decades of growth sitting in a tax-deferred account that forces large taxable distributions later. Converting now locks in today’s tax rate on that money and shields all future gains from taxation.
No Required Minimum Distributions
Traditional 401(k) accounts and traditional IRAs require you to start taking withdrawals once you reach age 73, regardless of whether you need the money. These required minimum distributions (RMDs) are calculated based on your account balance and life expectancy, and they count as taxable income each year. If your balance has grown substantially, RMDs can push you into a higher tax bracket and increase the amount of Social Security benefits subject to tax.
Roth IRAs have no required minimum distributions while you’re alive. You can leave the entire balance invested and growing tax-free for as long as you want. This gives you far more control over your retirement income. You withdraw when you choose, in the amounts you choose, and none of it adds to your taxable income. That flexibility can be especially valuable in years when you want to keep your adjusted gross income low, whether to qualify for certain tax credits, reduce Medicare premiums, or simply minimize your tax bill.
How the Conversion Is Taxed
When you roll over a traditional 401(k) to a Roth IRA, the pretax portion of the converted amount is added to your taxable income for that year. If your 401(k) balance is entirely pretax contributions and earnings (which is the case for most people), the full conversion amount gets taxed as ordinary income.
If your 401(k) contains both pretax and after-tax contributions, any distribution includes a proportional share of both. You cannot cherry-pick only the after-tax money. However, if you take a full distribution, you can direct the pretax amounts into a traditional IRA and the after-tax amounts into a Roth IRA, avoiding tax on the after-tax portion. Earnings on after-tax contributions are treated as pretax money and would go to the traditional IRA side.
There’s no income limit on conversions, which is one reason high earners use this strategy. Roth IRA contribution limits phase out above $165,000 for single filers and $246,000 for married couples filing jointly in 2025, but conversions bypass those limits entirely.
Timing the Conversion to Save on Taxes
The goal is to convert when your taxable income is lower than it will be in future years. Common windows include a year between jobs, a year when business income dips, early retirement before Social Security and RMDs begin, or any year with unusually large deductions.
You can also convert strategically by filling up your current tax bracket without spilling into the next one. For example, a single filer earning $150,000 in 2025 is in the 22% federal bracket. The 24% bracket begins at $197,300, so converting up to $47,300 would keep all the converted dollars taxed at the current rate. Waiting until late in the year to convert gives you a clearer picture of your total income before you decide how much to move.
You don’t have to convert everything at once. Spreading the conversion across multiple years lets you control how much taxable income you add each year. This is often called a “Roth conversion ladder,” and it’s particularly useful for people with large 401(k) balances who would jump several tax brackets with a single conversion.
The Five-Year Rule on Converted Funds
Roth IRA contributions can be withdrawn at any time without tax or penalty, but converted funds follow a separate rule. To withdraw the converted amount without a 10% early withdrawal penalty, you must wait at least five years from January 1 of the year you made the conversion. Each conversion starts its own five-year clock.
This rule primarily affects people under 59½. Once you reach 59½ and have had any Roth IRA open for at least five years, all withdrawals, including earnings, come out tax-free and penalty-free. If you’re already past that age, the five-year rule on conversions is less of a concern in practice, though it still technically applies to the earnings portion if the Roth account itself is less than five years old.
Benefits for Your Heirs
A Roth IRA can be significantly more valuable to your beneficiaries than a traditional 401(k). When someone inherits a traditional 401(k) or traditional IRA, every dollar they withdraw is taxed as ordinary income. Depending on the beneficiary’s own earnings, those inherited distributions could push them into a higher bracket.
Inherited Roth IRAs work differently. Withdrawals of contributions and converted amounts are tax-free. Withdrawals of earnings are also tax-free as long as the Roth account was open for at least five years before the original owner’s death. Most non-spouse beneficiaries must still empty the account within 10 years under current rules, but those 10 years of distributions generate no additional tax liability. That’s a meaningful difference for a beneficiary who is in their peak earning years and would otherwise owe income tax on every inherited dollar.
Because Roth IRAs have no RMDs during your lifetime, you can also leave the account untouched and let it compound for decades. A 401(k), by contrast, forces you to draw it down starting at 73, reducing what’s left for heirs.
When the Conversion May Not Make Sense
Paying tax now only saves money if your future tax rate on withdrawals would be higher. If you expect your income (and tax rate) to drop significantly in retirement, keeping the money in a pretax account and withdrawing it at that lower rate could leave you better off. This is especially true if a large conversion would push you into a much higher bracket today.
You should also consider where the money to pay the conversion tax comes from. Ideally, you pay the tax bill from non-retirement funds. If you have to use part of the converted amount to cover the taxes, you lose the benefit of that money compounding tax-free. For someone converting $100,000 at a 24% rate, that’s $24,000 that needs to come from somewhere, and pulling it from the conversion itself significantly reduces the long-term advantage.
Age and time horizon matter too. If you’re already in your 70s and plan to spend down the account quickly, the years of tax-free growth may not be enough to offset the upfront tax hit. The conversion tends to pay off most clearly when you have at least 10 to 15 years for the Roth balance to grow before you start withdrawing.