A Traditional 401(k) and a designated Roth 401(k) can hold the same investments, yet they place federal income tax at different points in time. Traditional employee deferrals generally reduce current taxable income and qualified withdrawals are taxed later. Designated Roth contributions are included in current gross income, while qualified distributions are generally tax-free. The useful comparison is therefore not simply which account shows the larger balance. It is how much spendable retirement money each choice may produce for the same present-day cost.
Use the BriskCalc 401(k) Calculator to test contribution, match and return assumptions. The calculations below are educational estimates, not tax or financial advice. Your plan document, eligibility, state taxes, withdrawal timing and future federal law can change the result.
Traditional and Roth 401(k) tax timing
The IRS describes pre-tax elective deferrals as employee contributions generally made from compensation before federal income tax. Designated Roth contributions are elective deferrals included in current gross income. According to the IRS Roth comparison chart, qualified Roth distributions require the applicable five-year holding period and a qualifying event, such as reaching age 59½, disability or death. A withdrawal that does not meet the applicable requirements needs separate tax review.
| Question | Traditional 401(k) | Designated Roth 401(k) |
|---|---|---|
| Federal income-tax treatment now | Employee elective deferral is generally pre-tax. | Employee elective deferral is included in current gross income. |
| Federal tax treatment later | Withdrawals of contributions and earnings are generally taxable. | Qualified distributions are generally tax-free. |
| Investment menu | Determined by the employer plan. | Usually selected from the same employer-plan menu. |
| Annual employee limit | Traditional and designated Roth elective deferrals share one aggregate employee limit. | |
The IRS retirement contribution guidance lists a 2026 basic elective-deferral limit of $24,500, or 100% of compensation if lower. Eligible participants may also have catch-up contribution options, including rules that can vary by age, compensation and plan terms. Check the current IRS limit and your plan before relying on a maximum because limits and Roth catch-up requirements can change by year and participant circumstances.
Source review: the IRS contributions page used for the 2026 limit was last reviewed or updated January 29, 2026. The IRS Roth comparison chart was last reviewed or updated September 3, 2025 and is used here for tax-treatment and qualified-distribution rules, not for its older contribution-limit table.
Two comparisons that prevent a misleading answer
There are two legitimate ways to compare the accounts, and they answer different questions.
Equal contribution
Enter the same dollar contribution in each account. If both accounts earn the same return, their displayed balances are equal before withdrawal taxes. The Roth balance may provide more spendable money if the distribution is qualified, because the Traditional balance still has an assumed future income-tax cost. This method is easy to understand, but the Roth contribution reduced take-home pay by more during the contribution years.
Equal take-home-pay cost
Hold the current reduction in spendable pay constant. Because a simplified Traditional deferral creates a current federal income-tax saving, a worker may be able to direct more gross salary to Traditional for the same estimated take-home-pay cost. This is the fairer tax-rate comparison, provided the larger contribution remains below the applicable annual limit.
For an end-of-year annual contribution, a simplified future-value formula is:
Future value = contribution × (((1 + return)^years − 1) ÷ return)
For the Traditional estimate, apply the assumed retirement tax rate:
Spendable Traditional value = future value × (1 − retirement tax rate)
For an equal present-day take-home cost, the simplified Traditional contribution is:
Traditional contribution = Roth contribution ÷ (1 − current marginal tax rate)
These formulas deliberately isolate federal income-tax timing. They do not model payroll taxes, state income tax, tax credits, deductions, investment fees, contribution timing within the year or changes in law.
Worked example: $8,000 per year for 30 years
Assume a worker can devote $8,000 of current after-federal-tax spending power each year, earns a 6% annual return, contributes at the end of each year and saves for 30 years. Assume a 22% current marginal federal rate and a 12% federal rate on Traditional withdrawals in retirement. These are illustration inputs, not a forecast.
The 30-year accumulation factor at 6% is approximately 79.058. An $8,000 annual Roth contribution therefore grows to approximately $632,465. If its distributions are qualified, this simplified example treats the full amount as spendable for federal income-tax purposes.
First consider an equal $8,000 Traditional contribution. It reaches the same $632,465 account balance. Applying the assumed 12% retirement rate produces an estimated $556,570 after federal income tax. That result makes Roth appear better, but the worker did not give up the same amount of current take-home pay: the simplified current cost of the Traditional contribution is only $6,240 at a 22% marginal rate.
Now compare equal current cost. An $8,000 Roth contribution has an $8,000 current after-tax cost. At a 22% current marginal rate, the comparable gross Traditional contribution is approximately $10,256: $8,000 ÷ (1 − 0.22). That annual amount grows to approximately $810,853. After applying the assumed 12% retirement rate, the estimated spendable Traditional value is approximately $713,551.
| Scenario | Annual contribution | Balance after 30 years | Estimated spendable value |
|---|---|---|---|
| Roth, $8,000 present-day cost | $8,000 | $632,465 | $632,465 if qualified |
| Traditional, equal nominal contribution | $8,000 | $632,465 | $556,570 at 12% |
| Traditional, equal simplified present-day cost | $10,256 | $810,853 | $713,551 at 12% |
The equal-cost result favors Traditional because the assumed retirement tax rate is lower than the current rate. If the future rate were higher, Roth could become more attractive. If the rates were equal and the current tax saving were fully contributed, the simplified tax result would be broadly equivalent. Real households also need to consider whether they will actually save the tax difference rather than spend it.
How to include an employer match
An employer match is additional plan money, not a reduction of the employee contribution. The IRS notes that a plan may provide matching contributions, such as a stated amount for each employee dollar deferred, and that plan terms control the arrangement. Model the employee contribution and employer contribution separately.
When comparing Traditional and Roth employee deferrals, use the same eligible match in both scenarios unless the plan document says otherwise. Confirm how the plan records and taxes matching contributions instead of assuming that an employee’s Roth election automatically determines the tax treatment of every employer dollar. Also check vesting rules before treating the entire projected match as money the employee will keep.
The calculator’s match result should not be interpreted as permission to exceed an IRS limit. Employee elective deferrals, employer contributions and total annual additions can involve different limits. The 2026 federal tax brackets guide can help identify a current marginal-rate assumption, while the federal income tax calculator provides a broader planning estimate.
Choosing assumptions instead of predicting tax law
No calculator can know a person’s retirement tax rate decades in advance. A useful analysis tests several scenarios rather than selecting one confident forecast.
- Current marginal rate: use the rate that applies to the next dollar of taxable income, not total tax divided by income.
- Retirement withdrawal rate: test a lower, equal and higher rate. Withdrawals can interact with other income and deductions.
- Return: use a range and keep investment fees visible. A higher assumed return magnifies small input differences.
- Time horizon: model the actual years until withdrawals may begin, not a generic retirement age.
- Contribution behavior: decide whether current Traditional tax savings will be contributed, invested elsewhere or spent.
- State taxes: current and retirement residency may change the comparison.
Splitting contributions between Traditional and Roth may provide tax diversification when the future rate is especially uncertain, but it is not automatically optimal. The appropriate allocation depends on plan options, contribution capacity and the user’s broader tax situation.
Common comparison mistakes
- Comparing equal account balances without recognizing that Roth required a larger current after-tax cost.
- Using an average tax rate where a marginal rate is required.
- Counting an employer match in one scenario but not the other.
- Assuming every Roth withdrawal will qualify for tax-free treatment.
- Adding the Traditional and Roth limits as if each account had a separate employee limit.
- Using an old annual contribution limit.
- Ignoring whether the Traditional tax saving will actually be saved.
- Treating a 30-year tax-rate assumption as a promise rather than a scenario.
FAQ
Can someone contribute to both account types?
A plan may allow contributions to both. The IRS comparison chart explains that employee elective deferrals can be split, but the combined amount remains subject to the aggregate limit. The plan must offer a designated Roth feature before an employee can use it.
Does Roth always win for a younger worker?
No. A long horizon increases the importance of tax treatment, but it does not reveal future tax rates. Current marginal rate, future withdrawal rate, contribution behavior, plan fees and qualified-distribution rules still matter.
Does Traditional always win when today’s tax rate is higher?
It may lead in a simplified equal-cost calculation, but only if the current tax saving is preserved and the future assumptions hold. Annual limits, state tax, other retirement income and changes in law can alter the result.
Should the employer match be entered as Roth money?
Do not infer the match’s tax treatment from the employee election. Use the employer’s current plan document and account records. In projections, display employee and employer amounts separately so the assumption can be reviewed.
Bottom line
Traditional versus Roth 401(k) is primarily a tax-timing decision. Compare both equal contributions and equal present-day cost, keep the employer match separate, and test several current and retirement tax rates. Then verify contribution limits and plan-specific rules against current IRS guidance. The result is a planning range, not a personalized recommendation.