The 60-second rule
At equal tax rates, the duel is a perfect tie — and that tie is the whole lesson. $15,000/yr out of pocket for 35 years at 7%, with a 27% combined rate now and in retirement: the Roth side grows to $2,073,553.18, tax-free. The Traditional side invests $20,547.95/yr pre-tax (the same $15,000 grossed up by the 27% deduction), grows to $2,840,483.80 before tax, and pays 27% at withdrawal — landing at $2,073,553.18. Identical to the dollar. The deduction you get today and the tax you pay later cancel exactly when the rates match.
The worked example, line by line
Setup: age 30 to 65 = 35 years; $15,000/yr out of pocket; 7% growth; 22% federal + 5% state now (27% combined); 22% federal + 5% state in retirement (27% combined); no employer match.
Line 1 — the annuity factor. FV factor = (1.0735 − 1) ÷ 0.07 = 138.2369. Every contributed dollar multiplies by this over 35 years — it is identical on both sides, so it sizes the prize but never picks the winner.
Line 2 — the Roth leg. $15,000 × 138.2369 = $2,073,553.18, and the Roth balance is tax-free at withdrawal. Done: $2,073,553.18 spendable.
Line 3 — the Traditional leg. Same $15,000 out of pocket buys $15,000 ÷ (1 − 0.27) = $20,547.95 of pre-tax contributions. Pre-tax future value = $20,547.95 × 138.2369 = $2,840,483.80. Withdrawal tax = 27%: $2,840,483.80 × 0.73 = $2,073,553.18.
Line 4 — the verdict. $2,073,553.18 − $2,073,553.18 = $0.00 — a tie. In the algebra the (1 − 0.27) you divide by going in and the (1 − 0.27) you multiply by coming out are the same number; they cancel. Equal rates → equal outcome, always, regardless of growth or horizon.
Branch — the high earner (32% now → 12% in retirement): now 37% combined, retirement 17%. Traditional: $15,000 ÷ 0.63 = $23,809.52/yr pre-tax → $3,291,354.25 before tax → × 0.83 = $2,731,824.02 after tax. Roth stays at $2,073,553.18. Traditional wins by $658,270.85 — deducting at 37% and withdrawing at 17% is the best trade on this page.
Branch — early career (12% now → 24% in retirement): now 17%, retirement 29%. Traditional: $15,000 ÷ 0.83 = $18,072.29/yr → $2,498,256.84 → × 0.71 = $1,773,762.35. Roth: $2,073,553.18. Roth wins by $299,790.82 — paying 17% now beats paying 29% later.
Branch — the $4,500 employer match: match future value = $4,500 × 138.2369 = $622,065.95 before tax → × 0.73 = $454,108.15 after tax. It lands on both sides equally — the verdict stays a tie. The match is always pre-tax, so it is verdict-neutral by construction.
Branch — no state tax: 22% federal both ends, states 0%. Traditional: $15,000 ÷ 0.78 → after-tax $2,073,553.18 — still a tie. The tie survives a lower rate level: what matters is the gap between now and retirement, not the absolute level.
Output · formula · meaning
| Output | Formula | What it means |
|---|
| Roth after-tax future value | out-of-pocket × annuity factor | $2,073,553.18 at the defaults — what you can actually spend. Roth withdrawals of contributions and qualified earnings are tax-free. |
| Traditional after-tax future value | (out-of-pocket ÷ (1 − ratenow)) × annuity factor × (1 − rateret) | $2,073,553.18 at the defaults — the pre-tax balance after the retirement tax bill. Identical to Roth when the two rates match. |
| Traditional pre-tax contribution | out-of-pocket ÷ (1 − ratenow) | $20,547.95/yr at the defaults — the apples-to-apples step most comparisons skip. $15,000 after-tax buys $20,547.95 before tax at a 27% rate. |
| Winner’s margin | |Roth − Traditional| after tax | $0.00 at the defaults — the dollar value of the rate gap. $658,270.85 in the 32%-now branch, $299,790.82 in the 12%-now branch. |
| Employer match, after tax | match × annuity factor × (1 − rateret) | $454,108.15 for the $4,500 preset — added to both sides, since matches are always pre-tax. Verdict-neutral. |
Who uses this
- The mid-career optimizer in the 32% bracket: runs the high-earner branch and sees Traditional winning by $658,270.85 — then checks whether she’ll really drop to 12% federal in retirement before going all-in.
- The 26-year-old in the 12% bracket: runs the early-career branch and learns Roth wins by $299,790.82 — the cheapest tax rate of her life is now, so she pays it.
- The 58-year-old in peak earnings: deducts at 37% combined today, withdraws at a lower rate after retiring — the page’s math says Traditional by a landslide, and the RMD section of the companion guide is her next read.
- The split-the-difference saver: hedges by contributing to both — Traditional up to the match, Roth beyond — because the one variable that decides everything (future tax rates) is unknowable.
Accuracy & limitations
The algebra is exact: the annuity factor is the standard future-value-of-an-annuity formula, and the tie at equal rates is a mathematical identity, not a rounding artifact. The model assumes constant tax rates and constant annual contributions and growth — real careers have raises, job changes, and bracket drift. Fees, fund expenses, and inflation are not modeled; the figures are nominal dollars. The employer match is always treated as pre-tax (that is how plans work). State-tax treatment of withdrawals varies — some states exempt retirement income, which would widen the retirement-rate gap in Traditional’s favor. The calculator does not model RMDs, Roth conversion ladders, estate planning, or Social Security taxation — see the companion guide for the RMD angle. This is a comparison calculator, not tax advice.
Cite this calculatorBright Side Kit. “Roth vs Traditional 401(k): 2026 Full After-Tax Verdict | Bright Side Kit.”
brightoolbox.com, 2026.
Bright Side Kit. "Roth vs Traditional 401(k): 2026 Full After-Tax Verdict | Bright Side Kit." https://brightoolbox.com/roth-vs-traditional-401k/ Accessed October 24, 2026.Data sources- IRS Notice 2025-67 — 2026 elective deferral limit $24,500 (under 50); catch-up $8,000 (50+); super catch-up $11,250 (ages 60–63).
- SECURE 2.0 Act of 2022 — RMD age 73 (born 1951–1959), 75 (born 1960 or later); Roth 401(k) balances exempt from RMDs starting in 2024.
- Future value of an annuity — PMT × ((1+r)n − 1) ÷ r, the standard compounding formula behind every figure on this page.
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Frequently asked questions
Can I split my contributions between Roth and Traditional 401(k)?
Yes — and it’s often the smartest hedge. The $24,500 2026 under-50 limit is one shared cap across both: put $10,000 in Roth and $14,500 in Traditional, or any mix. Many savers do Traditional up to the employer match, then Roth beyond it — since the one variable that decides the duel (your future tax rate) is unknowable, diversification across tax treatments is rational.
What is the 401(k) contribution limit for 2026?
$24,500 if you’re under 50 — split however you like between Roth and Traditional. At 50+ add the $8,000 catch-up for $32,500; ages 60–63 get the $11,250 super catch-up for $35,750, if your plan allows it. The page’s $15,000 default sits comfortably under the cap.
Does my employer match go into Roth or Traditional?
Pre-tax — always. Employer matches land in the Traditional (pre-tax) side of your account even if every dollar you contribute is Roth, and they’re taxed at withdrawal. That’s why the calculator’s $454,108.15 match value lands on both sides equally: it’s verdict-neutral by the rules of the plan, not by choice.
Do Roth 401(k)s have required minimum distributions?
Not anymore. The SECURE 2.0 Act eliminated RMDs on Roth 401(k) balances starting in 2024 — before that, they had them and people rolled to Roth IRAs to escape them. Traditional 401(k)s still face RMDs at 73 (born 1951–1959) or 75 (born 1960+). If you plan to leave money untouched deep into retirement, that asymmetry is worth real money beyond this page’s math.
What is a backdoor Roth, and does it change this comparison?
It’s a different door into the same room. The backdoor Roth is an IRA maneuver — contribute after-tax to a Traditional IRA, convert to Roth — for high earners blocked from direct Roth IRA contributions. It doesn’t change the 401(k) duel on this page; it’s an extra Roth bucket on top of it. (Watch the pro-rata rule if you hold pre-tax IRA money.)
If tax rates are equal, is it really a perfect tie?
In this model, yes — it’s an identity, not an estimate. The (1 − rate) you divide by going in and the (1 − rate) you multiply by coming out are the same number, so they cancel for any growth rate and any horizon. In real life the differentiators are RMDs, estate treatment, withdrawal flexibility, and the fact that nobody’s rate stays flat for 35 years — that’s what the branches are for.
What if I retire to a state with no income tax?
That’s a retirement-rate cut — Traditional’s favorite move. Dropping a 5% state rate in retirement is the same math as the page’s early-career branch in reverse: every point shaved off the retirement rate hands the Traditional side more of its $2,840,483.80 pre-tax balance. Enter 0% in the retirement state field to price your own move.