Quick Summary
A guide to comparing traditional and Roth 401(k) contributions - the tax tradeoffs, how to estimate which is better, and why splitting between both can make sense.
Do you want to pay taxes now or later? That is the entire 401(k) vs. Roth 401(k) question, stripped of jargon. The answer depends on one thing you can estimate but never know for certain: whether your tax rate will be higher or lower in retirement than it is today.
The 401(k) vs. Roth 401(k) Calculator compares both options using your specific numbers. No signup required.
A Decision Tree
Before diving into the math, here is a quick framework:
If your tax rate is clearly higher now than it will be in retirement - traditional likely wins. You avoid taxes at a high rate now and pay at a lower rate later.
If your tax rate is clearly lower now than it will be in retirement - Roth likely wins. You pay taxes at today’s low rate and withdraw tax-free later.
If you genuinely do not know - splitting between both is a reasonable hedge.
Most of this article is about figuring out which scenario applies to you. The calculator handles the math once you have a guess.
Why the Math Is Symmetric
When tax rates stay the same, both options produce identical after-tax income. This surprises people, but the math is straightforward.
Traditional path: $10,000 pre-tax contribution in the 22% bracket. Grows to $40,000 over 25 years at 7%. Withdraw and pay 22% tax: $31,200 after tax.
Roth path: Same $10,000 income. Pay 22% tax first, leaving $7,800 to contribute. Grows to $31,200 over 25 years at 7%. Withdraw tax-free: $31,200.
Identical. The order of operations - taxing before or after growth - does not change the result when the rate is the same. This means the entire decision hinges on the difference between your current and future rate.
Scenarios Where Traditional Wins
High earner approaching retirement. Someone in the 32% bracket with 5-10 years left before retiring at a lower spending level gets an immediate tax break at a high rate and pays at a lower rate. The spread is wide and the time horizon is short, which limits Roth’s growth advantage.
Large income drop expected in retirement. A household spending $150,000 during working years but planning to live on $60,000 in retirement will likely drop several tax brackets. Traditional contributions saved at 32% and withdrawn at 12% or 22% create significant tax savings.
Moving from a high-tax state to a no-tax state. Contributing in California (up to 13.3% state tax) and withdrawing in Texas or Florida (0%) adds state tax savings on top of any federal advantage.
Scenarios Where Roth Wins
Early career in a low bracket. Someone earning $45,000 in the 12% bracket who expects income growth over the next twenty years is locking in a low tax rate. If they eventually reach the 24% or 32% bracket, paying 12% now looks like a bargain in hindsight.
Concern about future tax rates. If you believe rates will rise generally - given long-term government debt trends - paying today’s known rate removes that uncertainty. Nobody knows what rates will look like in 2050, but current rates are historically moderate.
Large traditional balances already. Required minimum distributions from big traditional accounts can push retirees into higher brackets unexpectedly. Roth money has no RMDs and does not count as taxable income, which keeps other tax-sensitive calculations (Social Security taxation, Medicare premiums) lower.
Running the Comparison
Here is a concrete example for someone trying to decide:
Profile: Age 35, $90,000 salary, 24% marginal federal rate, plans to retire at 65, expects a 22% rate in retirement.
Contributing $9,000/year (10% of salary) at 7% return for 30 years:
Traditional path: Tax savings of $2,160/year now. Balance at 65: ~$849,000. After 22% tax on withdrawals: ~$662,000 in spending power.
Roth path: No tax break now, costing $2,160 more annually. Balance at 65: ~$849,000. All tax-free: $849,000 in spending power.
The Roth produces $187,000 more in after-tax dollars. But to make this comparison fair, you have to ask: what happens with the $2,160/year the traditional path freed up? If invested at 5.5% after-tax return for 30 years, it grows to about $162,000.
Net Roth advantage: roughly $25,000 in this scenario. The gap is modest because the rate difference (24% now vs. 22% later) is small. If the future rate were 15%, traditional wins. If 32%, Roth wins by a much larger margin.
The Case for Doing Both
Here is a detail that simplifies the decision: you can split.
Many plans allow directing some percentage to traditional and some to Roth. The combined total still cannot exceed $23,500 in 2025 ($31,000 with catch-up at 50+). This provides:
Tax diversification. In retirement, you can pull from whichever account makes that year’s tax situation more favorable. Low-income year? Draw from the traditional side at a low rate. High-income year? Use Roth.
Protection against uncertainty. Nobody knows what tax policy will look like in twenty or thirty years. Having both account types means you benefit either way.
RMD management. Smaller traditional balances mean smaller required minimum distributions, keeping taxable income more controllable in later years.
A common approach: contribute enough to the traditional side to reduce AGI below key thresholds (for deductions or credits), and put the rest in Roth.
One Thing People Forget
Regardless of whether you choose traditional or Roth for your own contributions, the employer match always goes into the traditional (pre-tax) side. Even someone contributing 100% Roth will end up with both account types.
This means most people will have a mix anyway. The question is just the ratio, and the ratio can change year to year as income and circumstances shift.
The Retirement Financial Planning Template helps model different contribution strategies alongside broader retirement projections.
Roth & 401(k) Deep Dives
- Roth Conversion Calculator: When Converting Makes Sense - When a Roth conversion is advantageous and how to find the optimal conversion amount
- Roth IRA Growth Calculator: See Your Tax-Free Future - How tax-free compounding works and why starting early matters
- 401(k) Calculator: How Contributions Grow Over a Career - Modeling 401(k) growth with employer matching over a full career