Roth vs Traditional: IRA and 401k Compared

The Roth vs traditional question is the most commonly debated topic in personal finance, and it generates more confusion than it should. The underlying mechanics are simple. The application to your specific situation is where it gets nuanced.

Both the IRA and 401k come in Roth and traditional versions. The rules differ slightly between the two account types, but the core tax question is identical: do you want to pay taxes on this money now, or later? Everything else follows from that. For the question of which accounts to prioritize before getting to the Roth vs traditional decision, see 401k vs IRA vs HSA — which to max first.

The Core Mechanic

Traditional accounts give you a tax deduction today. You contribute pre-tax dollars, the money grows tax-deferred, and you pay ordinary income tax on every dollar you withdraw in retirement. The tax is deferred, not eliminated.

Roth accounts give you no deduction today. You contribute after-tax dollars, the money grows tax-free, and qualified withdrawals in retirement are completely tax-free — principal and earnings both. You pay the tax upfront and never again.

If your tax rate is identical now and in retirement, the two approaches produce mathematically equivalent outcomes. Contributing $1,000 pre-tax to a traditional account and paying 22% tax on withdrawal produces the same after-tax amount as contributing $780 after-tax to a Roth — $780 being $1,000 minus 22% tax paid now. The math is symmetric when rates are equal.

The decision therefore comes down to whether your tax rate will be higher now or in retirement. Pay tax at the lower rate. That is the entire framework.

Why Predicting Your Retirement Tax Rate Is Hard

The challenge is that your retirement tax rate depends on factors that are genuinely difficult to predict 20 or 30 years out.

Your retirement income sources determine your taxable income. A large traditional 401k produces large required minimum distributions starting at 73, which create taxable income whether you need the money or not. Social Security becomes partially taxable above certain income thresholds. A pension adds taxable income on top of all of that. Someone with a large pre-tax portfolio, a pension, and Social Security can find themselves in a surprisingly high bracket in retirement despite having lower overall spending than their working years.

Tax rates themselves can change. Current rates were reduced in 2017 and are scheduled to revert to higher levels after 2025 unless Congress acts. Nobody knows with certainty what the rate schedule will look like in 2045. Hedging between Roth and traditional — holding both — reduces the risk that a future rate change disadvantages your entire retirement portfolio.

State taxes add another layer. Some states exempt retirement income from state income tax. Others tax all income equally. If you plan to retire in a different state than you currently live in, the state tax differential can be significant.

When Traditional Wins

The traditional account is the better choice when your current marginal tax rate is meaningfully higher than what you expect to pay in retirement.

High earners in their peak years are the clearest case. Someone in the 32% or 37% bracket today who expects a much lower income in retirement — where the 22% or even 12% bracket applies — saves 10 to 25 percentage points of tax by deferring. The deduction today is worth more than the tax-free treatment later because the rates are so different.

People with modest expected retirement income also favor traditional. If your Social Security plus small pension adds up to $30,000 per year and you plan to live simply, your retirement taxable income may be low enough that traditional withdrawals face minimal tax. The deduction you got during your working years at 22% or higher was worth more than the 10% or 12% you will pay on moderate retirement withdrawals.

Short time horizons favor traditional too. The Roth's advantage compounds over decades of tax-free growth. With only 5 or 10 years to retirement, the compounding differential is smaller and the upfront deduction from the traditional account carries more weight.

When Roth Wins

The Roth account is the better choice when your current tax rate is low relative to what you expect in retirement — or when you value the flexibility and control it provides regardless of the rate comparison.

Early career earners are the strongest case for Roth. Someone in their 20s or early 30s in the 12% or 22% bracket who expects their income — and therefore their tax rate — to rise significantly over their career is paying tax at the lowest rate they will likely ever face. Every dollar contributed to a Roth now locks in that low rate on all future growth.

People building large pre-tax portfolios should consider Roth as a diversifier. If you have been maxing a traditional 401k for 20 years, you have substantial pre-tax assets that will generate taxable RMDs at 73 whether you want them or not. Adding Roth contributions diversifies your tax exposure and gives you flexibility to manage your taxable income in retirement.

Early retirees favor Roth for the access flexibility. Roth contributions can be withdrawn penalty-free at any age. For FIRE practitioners bridging the gap before 59½, Roth contribution balances are immediately accessible without penalty. Traditional accounts are locked until 59½ without penalty except through specific workarounds. For the next question after maxing Roth — where to put additional taxable savings — see the comparison of brokerage vs Roth IRA after maxing your accounts.

The Roth also has no required minimum distributions during the owner's lifetime. For people who do not need their retirement savings to live on — who plan to pass assets to heirs — the Roth's absence of RMDs allows the account to compound untouched indefinitely. Heirs inherit Roth IRAs income-tax-free, though they must take distributions over 10 years under current law.

The IRA-Specific Rules

The Roth IRA has income limits that the Roth 401k does not. In 2026, direct Roth IRA contributions phase out for single filers between $150,000 and $165,000 MAGI, and for married filers between $236,000 and $246,000. Above those limits, direct contributions are not allowed.

The traditional IRA deduction also phases out at higher incomes when you have access to a workplace retirement plan. Single filers covered by a workplace plan lose the deduction between $79,000 and $89,000 MAGI. Married filers lose it between $126,000 and $146,000. Above those thresholds, traditional IRA contributions are still allowed but are non-deductible — you contribute after-tax dollars and get no current deduction, which removes most of the traditional IRA's advantage.

Non-deductible traditional IRA contributions are the foundation of the backdoor Roth IRA strategy: contribute to a traditional IRA without deducting it, then immediately convert to Roth. The conversion is taxable only on any earnings between contribution and conversion — typically near zero if done quickly. This allows high earners above the Roth income limit to effectively make Roth IRA contributions.

The pro-rata rule complicates backdoor Roth conversions for people who have existing pre-tax IRA balances. If you have $100,000 in a traditional IRA and make a $7,000 non-deductible contribution, only about 6.5% of any conversion is tax-free — the rest is taxable in proportion to the pre-tax balance. People with large traditional IRA balances who want to use the backdoor Roth may need to first roll the traditional IRA into a 401k to clear the pro-rata calculation.

The 401k-Specific Rules

Roth 401k contributions have no income limits — anyone can make Roth 401k contributions regardless of income, unlike the Roth IRA. This makes the Roth 401k available to high earners who are phased out of the Roth IRA.

Until recently, Roth 401ks had required minimum distributions at 73, same as traditional 401ks. SECURE 2.0, passed in 2022, eliminated RMDs for Roth 401k accounts starting in 2024. Roth 401k balances can now be left to compound without forced distributions, matching the Roth IRA's behavior.

Employer match contributions always go into a traditional pre-tax account regardless of whether you contribute Roth or traditional. If you make Roth 401k contributions, the employer match is still pre-tax. You will end up with both Roth and traditional balances in your 401k even if you elect 100% Roth contributions.

The Practical Answer for Most People

For someone in the 22% bracket in their 30s or early 40s with a long career ahead, the Roth is usually the better choice — the rate is moderate, the time horizon for tax-free growth is long, and the flexibility has real value. The traditional starts making more sense as income rises into the 32% bracket and above, or as retirement approaches and the compounding advantage shrinks.

For most people, the best answer is both. Max the employer match in the 401k regardless of type. Use the Roth IRA up to the contribution limit if eligible. Split 401k contributions between Roth and traditional if your plan allows it. Tax diversification across account types reduces the risk that any single rate outcome — rates going up, rates going down, large RMDs in retirement — damages your plan significantly.

At NumberToRetire.com, the IRA section accepts a contribution amount and projects it forward as part of your total retirement balance. You can run the projection twice — once treating the IRA balance as Roth (tax-free in retirement) and once as traditional (taxable on withdrawal) — and compare the after-tax retirement income. The difference is your Roth vs traditional decision in your specific numbers, not in the abstract.