Roth vs Traditional: Which One?

Everyone Has an Opinion. Most of Them Are Wrong.

“Just do Roth, it’s always better.” You’ve heard this at some point, from a coworker, a subreddit, a finance influencer who clearly hasn’t looked at a tax bracket since 2019. It’s well-intentioned advice that happens to be wrong for a significant slice of the people receiving it.

Roth is not always better. Traditional is not always better. The answer is a math problem, and the key input is one you can actually estimate: your marginal tax rate now versus your marginal tax rate in retirement. If you know that, everything else falls into place.

Let’s do the math.

How Each One Works (30-Second Version)

Traditional 401k / Traditional IRA: You contribute pre-tax dollars. Your taxable income drops by the contribution amount this year. The money grows tax-deferred. You pay income tax on every dollar you withdraw in retirement.

Roth 401k / Roth IRA: You contribute post-tax dollars. No deduction this year, you pay taxes now. The money grows tax-free. Withdrawals in retirement are completely tax-free.

The 2026 limits:

• 401k (either flavor): $24,500 employee contribution limit
• IRA (either flavor): $7,500 limit (Roth IRA income phases out at $153k$168k single, $242k$252k married)

The choice of Roth vs Traditional on your 401k doesn’t affect how much you can contribute. You’re just deciding when the IRS gets its cut.

The Break-Even Logic

Here’s the clean version: if your tax rate is the same now and in retirement, Roth and Traditional are mathematically identical.

Let’s prove it. You’re in the 24% bracket and you have $10,000 pre-tax to invest.

Traditional path:

• Contribute $10,000 pre-tax
• Grows to $50,000 over 25 years (5x for easy math)
• Withdraw $50,000, pay 24% tax: keep $38,000

Roth path:

• Pay 24% tax now: invest $7,600 after-tax
• Grows to $38,000 over 25 years (same 5x)
• Withdraw $38,000 tax-free: keep $38,000

Same outcome. The math only diverges when the tax rates differ. So the entire game is predicting the spread between your rate today and your rate when you’re pulling money out.

Roth wins if: your retirement tax rate > your current rate Traditional wins if: your retirement tax rate < your current rate Coin flip if: they’re roughly equal

The Case for Traditional (Peak-Earner Years)

If you’re an engineer earning $180,000 in 2026, you’re in the 22% or 24% federal bracket depending on filing status. Add your state tax if you’re in California or New York, and your marginal rate could be 30 to 37% on the next dollar you earn.

That’s probably not what your retirement spending looks like. A lot of FIRE-minded tech workers plan to spend $80,000$120,000 in retirement, which, even in 2026 dollars, sits at 12 to 22% federal brackets. If you live in a no-income-tax state in retirement, the math gets even more favorable.

The worked example:

Jamie is a software engineer, $180,000 salary, single filer, 24% federal bracket, lives in a state with 5% income tax. Effective marginal rate: ~29%.

Jamie maxes the 401k: $24,500 in traditional contributions.

Tax savings this year: $24,500 × 0.29 = $7,105 back in Jamie’s pocket (or more accurately, not taken from Jamie’s paycheck).

In retirement, Jamie plans to withdraw $90,000/year. Federal tax on that (standard deduction reduces taxable income): roughly 15 to 18% effective rate. If Jamie moves to Florida or Nevada, add zero state tax.

The spread between 29% now and ~17% in retirement is 12 percentage points. On $24,500 per year, over a 25-year career, that spread compounds into a substantial advantage for Traditional.

The Case for Roth (Early Career and Tax Diversification)

The Traditional argument assumes your income goes down in retirement. That’s usually true. But three things can flip the math:

1. You’re early career. If you’re 23 and earning $85,000, you might be in the 12% or 22% bracket right now. That might be the lowest tax rate you see for the next 30 years. Paying taxes at 22% now to get tax-free withdrawals later, when you’re presumably earning more, is a good bet.

2. You’ll have other income in retirement. Social Security is taxable (up to 85% of benefits, depending on income). A pension. Rental income. Dividends from a taxable brokerage. The more taxable income sources you stack in retirement, the higher your effective rate. If you’ve built a large Traditional balance and you’re also drawing Social Security, you might be in the 22 to 24% bracket in retirement anyway. The savings rate assumptions don’t always pan out the way you model them at 35.

3. Required Minimum Distributions (RMDs). Traditional accounts force you to start taking taxable withdrawals at age 73, whether you need the money or not. If your Traditional balance is $2M, the RMD in year one is around $75,000. Mandatory. Taxable. Roth accounts (specifically Roth IRAs, the 401k version still has RMDs unless you roll to a Roth IRA) have no RMDs. The money can sit and grow until you actually need it, or pass to heirs tax-free.

The Real Answer: Tax Diversification

Here’s what the Roth-or-Traditional debate misses: you don’t have to pick one.

The optimal strategy for most tech workers isn’t “all Roth” or “all Traditional”, it’s building both buckets so you have flexibility in retirement to control your taxable income year by year.

In a given retirement year, you can:

• Pull from Traditional up to the top of the 12% bracket (2026: $50,400 single)
• Pull remaining income needs from Roth tax-free
• Blend to keep yourself under whatever threshold triggers Medicare premium surcharges (IRMAA starts at $109,000 in 2026)

If all your money is in Traditional, you’re locked into taxable withdrawals whether or not it’s efficient that year. If all your money is Roth, you’ve potentially overpaid taxes during peak earning years. Having both gives you dials to turn.

The practical heuristic:

• Under 30, or in the 12% bracket: lean Roth
• 30s, 40s, 22%+ bracket, high earnings: lean Traditional
• High earner who’s already done the Traditional math: hedge with at least 20 to 30% of new contributions going Roth

One Thing That’s Always Traditional: The Employer Match

This one’s non-negotiable. Your employer match goes into a Traditional (pre-tax) bucket regardless of which type of 401k you’re contributing to. You don’t get to choose. When you withdraw the match and its earnings in retirement, it’s taxable.

This means every 401k participant already has some Traditional exposure built in. If you’re contributing 100% to Roth 401k, your account is still a blend, your contributions are Roth, the match is Traditional.

It also means the “all Roth” strategy isn’t quite as clean as it sounds when you account for what’s actually in the account.

Roth IRA Income Limits, and the Backdoor

One practical wrinkle: if you earn over $168,000 (single) or $252,000 (married) in 2026, you can’t contribute directly to a Roth IRA at all. The income limit phases out between $153k$168k single.

The Traditional IRA has no income limit for contributions, but the deductibility phases out too if you have a workplace plan. Above $91,000 single / $149,000 married, traditional IRA contributions aren’t deductible, you’re contributing after-tax with no upfront benefit. (Phase-out begins at $81,000 single / $129,000 MFJ.)

The solution for high earners who want a Roth IRA: the backdoor Roth. Contribute to a Traditional IRA (non-deductible), then convert it to a Roth IRA. It’s a legal workaround that effectively lets anyone do a $7,500 Roth IRA contribution regardless of income. There’s no limit on conversions. The mechanics aren’t complicated; the main gotcha is the pro-rata rule if you already have traditional IRA balances.

If your income is over the Roth IRA limit, the 401k Roth option has no income restriction, you can contribute Roth 401k regardless of what you earn. The Roth IRA limit and the Roth 401k limit are separate rules.

A Framework That Actually Helps

Stop trying to pick one forever. Think about it in phases:

The pre-retirement Roth conversion window is underrated. If you retire at 55 and don’t touch Social Security until 67, you have a ~12-year window where your taxable income might be very low. That’s the time to systematically convert Traditional to Roth at lower rates, filling up the 12% or 22% bracket each year. It’s essentially buying down future RMDs.

The Bottom Line

Roth is better when your tax rate goes up in retirement. Traditional is better when it goes down. For most tech workers in peak earning years, Traditional wins on the math. For early-career engineers or people who expect high retirement income, Roth looks better.

The right answer for most people is: Traditional 401k during high-earning years, Roth IRA via backdoor every year regardless, and a mental note to revisit the split every time your compensation bracket shifts.

What you should do today:

1. Check your current marginal tax rate: federal + state, not just the bracket
2. Estimate your likely retirement income (include Social Security, don’t guess low)
3. If your marginal rate is 24%+, make sure you’re not leaving the Traditional 401k deduction on the table
4. If you’re under 30 or in the 22% bracket, tilt Roth
5. Max the Roth IRA via backdoor regardless: $7,500 per year is always worth doing

The financial services industry loves Roth because clients love hearing “tax-free.” It’s a clean story. But tax-free growth doesn’t help you if you overpaid to get it. Run your own numbers before you take anyone’s default.