Roth vs Traditional 401k Calculator (With Employer Match)
Roth or traditional 401(k) comes down to two numbers: your marginal tax rate today and the tax rate you will pay on withdrawals in retirement. For the same cost to your paycheck, traditional ends with more to spend when the retirement rate is lower than today’s rate, Roth ends with more when it is higher, and at equal rates they tie to the cent. An employer match does not change that comparison, because the match goes into the pre-tax side of the plan whichever you choose. In the illustrative example below - 24% today, 18% in retirement - traditional comes out $56,676.47 ahead after 30 years.
The formula
Compare the two at the same take-home cost, because that is what you actually give up:
- Traditional, after tax = contribution x growth factor x (1 - retirement tax rate)
- Roth = contribution x (1 - today’s tax rate) x growth factor
- Growth factor = ((1 + return)^years - 1) / return, for a deposit at the end of each year
The growth factor is the same on both sides, so it cancels out of the decision. What is left is (1 - retirement rate) against (1 - today’s rate). If the retirement rate is the lower one, traditional wins; if today’s rate is lower, Roth wins. The return, the number of years and the size of the contribution change how big the gap is, never which side it favors.
In a spreadsheet, with today’s rate in B1, the retirement rate in B2, the
contribution in B3 and the growth factor in B4: traditional is
=B3*B4*(1-B2) and Roth is =B3*(1-B1)*B4.
Worked example: same take-home cost
These tax rates and returns are illustrative, not brackets and not a forecast. Every tax rate in this calculation is yours to enter; nothing here works out your bracket.
A $10,000 traditional contribution at a 24% combined marginal rate costs $7,600 of take-home pay, because the $2,400 of income tax on it is deferred. So the fair Roth comparison is $7,600 a year. Both grow at 7% for 30 years (a growth factor of 94.46):
| Traditional | Roth | |
|---|---|---|
| Take-home pay given up each year | $7,600 | $7,600 |
| Goes into the account each year | $10,000 | $7,600 |
| Balance after 30 years at 7% | $944,607.86 | $717,901.98 |
| Tax on withdrawal at 18% | $170,029.42 | none |
| Yours to spend | $774,578.45 | $717,901.98 |
Traditional is ahead by $56,676.47, and the reason is entirely the two rates: $10,000 x 94.46 x (24% - 18%) gives the same $56,676.47.
Now hold everything else and change only the retirement rate:
| Tax rate in retirement | Traditional, after tax | Roth | Ahead |
|---|---|---|---|
| 12% | $831,254.92 | $717,901.98 | Traditional |
| 18% | $774,578.45 | $717,901.98 | Traditional |
| 24% | $717,901.98 | $717,901.98 | Tie |
| 30% | $661,225.50 | $717,901.98 | Roth |
The Roth column does not move. The traditional column crosses it exactly at 24% - today’s rate. That is the whole decision in one table.
With an employer match
The question behind a Roth vs traditional 401k calculator with employer match is whether the match changes the answer. It does not, and the reason is written into the rules. The IRS page “Retirement topics - Designated Roth account” says: “Matching contributions and profit-sharing contributions may not be made directly to the designated Roth account.” So the match lands in the pre-tax side of the plan and is taxed when you withdraw it, whichever way you send your own money.
Illustrative example: a salary of $80,000, 6% contributed, and an employer that matches 50% of contributions up to 6% of salary - a $2,400-a-year match on your $4,800. Same rates as above.
| After tax, at retirement | Choose traditional | Choose Roth |
|---|---|---|
| Your $4,800 a year | $371,797.65 | $453,411.77 |
| Employer’s $2,400 a year (pre-tax either way) | $185,898.83 | $185,898.83 |
| Total | $557,696.48 | $639,310.60 |
| Take-home pay given up each year | $3,648 | $4,800 |
The match row is identical in both columns: $185,898.83 after tax either way. Choosing Roth ends $639,310.60 against $557,696.48, but it costs $1,152 more take-home pay a year, so the totals are not a fair comparison on their own.
To compare at the same take-home cost, the traditional saver would put in $6,315.79 a year (7.89% of salary) to give up the same $4,800 as the Roth saver. That is still above the 6% the match is capped at, so the match stays $2,400. Traditional then ends at $675,106.27, ahead of Roth by $35,795.67 - and that gap is exactly $6,315.79 x 94.46 x (24% - 18%), the same formula as without a match. The match drops out.
What the match does decide is how much to contribute: enough to collect the whole match, under either choice. Two caveats. The SECURE 2.0 Act lets a plan offer Roth treatment of employer contributions; if your plan offers it and you elect it, the match is taxed now instead, which this comparison does not model. And vesting rules can mean the match is not yours until you have worked there long enough.
The insight: it is a bet on one number
Everything above turns on your retirement tax rate, which cannot be looked up today. It depends on future tax law, where you live then, and what else you will have coming in. Three ways the comparison shifts once you look closer:
- If you contribute the same dollars either way. At the full $24,500 limit (before any catch-up), the same-take-home comparison is not available: a Roth $24,500 costs $24,500 of take-home, a traditional $24,500 costs $18,620 at a 24% rate, and you cannot put $32,237 into a traditional account to match. If the traditional saver invests the $2,400 a year of tax saved on a $10,000 contribution in a taxable account, with gains taxed at 15% at the end, traditional totals $978,078.45 against the Roth’s $944,607.86, and the break-even retirement rate falls from 24% to 21.54%. That only counts if the saving is actually invested.
- The limit is shared. Per the same IRS page, “Total contributions to the pre-tax elective deferral and Roth accounts cannot exceed the annual contribution limit.” For 2026 that limit is $24,500, plus catch-up contributions of $8,000 at age 50 and over, or $11,250 at ages 60 to 63 (IRS release IR-2025-111). Splitting does not raise it.
- Not knowing is a reason to split. Putting part of the money in each account narrows the range of outcomes when you cannot pin the retirement rate down. It never wins outright; it hedges.
How these were calculated
Each contribution is made at the end of the year and grows at the same yearly return in either account; the growth factor is ((1 + return)^years - 1) / return, checked against a year-by-year loop. The traditional balance is taxed once, at the single retirement rate entered; the Roth balance is taken as tax-free. The match is modeled as pre-tax, per the IRS designated Roth account page. In the invested-saving case, gains in the taxable account are taxed once at the end; yearly tax on dividends is ignored, which flatters traditional slightly. The 2026 limits ($24,500, $8,000, $11,250) are from IRS newsroom release IR-2025-111.
Every figure on this page was computed twice - once by the code behind the calculator pack below, once by a separate implementation written from the formulas - and the two agree to the cent. The salary, contribution, match terms, return, years and every tax rate are illustrative, not forecasts, brackets or figures for anyone in particular. None of this is financial, legal or tax advice; your plan documents, a tax professional and the IRS are the authorities for your own situation.
If you want to run this on your own rates and your own plan - same paycheck cost, the break-even retirement rate, the match, investing the tax saving, what it takes to reach the limit, the paycheck difference and a split - the pack below does it in linked spreadsheets with every formula visible.