At a glance
Quick answer
A traditional 401(k) contribution can defer current federal income tax because the contributed amount generally is not included in federal taxable wages. It normally remains subject to Social Security and Medicare tax, so this comparison leaves payroll tax unchanged. Enter annual wages before the tested traditional contribution, not Form W-2 box 1 wages after the deferral, and enter the contribution separately. The result is a current year tax difference, not the value of the retirement account and not a promise of permanent savings. Your employer's plan document, payroll records, age, other elective deferrals, and the annual IRS limit determine what may actually be contributed. This page does not decide participation, contribution, matching, or distribution eligibility.
How the calculation works
Income tax changes while payroll tax stays on the same wages
The comparison first calculates federal income tax using the entered wages before the tested contribution. It then excludes the traditional 401(k) amount from federal taxable income and recalculates the return. Form W-2 box 1 generally already reflects a traditional deferral, so entering box 1 and then entering the same contribution would subtract it twice. Employee Social Security and Medicare tax continue to use the original wages in both columns. That distinction matters because a $10,000 traditional deferral does not produce an extra 7.65% payroll tax saving in this comparison. The income tax change depends on the brackets crossed by those $10,000 of deductions. If all affected dollars sit in the 24% bracket, the modeled current income tax reduction is $2,400.
The contribution limit is separate from the tax comparison
For 2025, the basic employee elective deferral limit for a 401(k) is $23,500. A participant age 50 or older may have a $7,500 catch up limit, while the higher catch up limit for ages 60 through 63 is $11,250. For 2026 planning, the basic limit is $24,500, the general age 50 catch up is $8,000, and the age 60 through 63 amount is $11,250. The calculator rejects only amounts above the highest possible age based total, $34,750 for 2025 or $35,750 for 2026. It does not determine whether a person qualifies for any catch up. Plan rules, compensation, other deferrals, and payroll timing can require a lower amount.
Current deferral is not lifetime tax savings
Traditional contributions generally postpone income tax until distributions are included in income. This page shows only the current federal comparison. It does not project investment returns, future tax brackets, required minimum distributions, early distribution tax, loans, hardship withdrawals, Roth treatment, employer matching, or vesting. A result called savings is therefore the difference between two current year estimates. It is not the account balance and does not subtract the contribution from take home cash. State rules can also differ from the federal treatment. Review the contribution shown on payroll records and the plan's year end reporting before relying on the estimate.
2025 and 2026 values
Tax year 2025
2025 final limits and federal values
The 2025 final view uses a $23,500 basic employee deferral limit, a $7,500 general catch up for age 50 or older, and an $11,250 catch up for ages 60 through 63. It applies the final 2025 standard deductions and ordinary brackets, including the $15,750 single standard deduction and the 24% single bracket from $103,350 to $197,300 of taxable income.
Tax year 2026
2026 planning limits and federal values
The labeled 2026 planning view uses a $24,500 basic employee deferral limit, an $8,000 general age 50 catch up, and the $11,250 amount for ages 60 through 63. It combines those limits with planning tax values, including a $16,100 single standard deduction and a 24% single bracket from $105,700 to $201,775.
Recalculate it yourself
Worked example
$10,000 traditional deferral at $200,000 of wages
A single filer enters $200,000 of annual wages before a tested $10,000 traditional 401(k) contribution for 2025.
- Taxable income before the contribution = $200,000 wages − $15,750 standard deduction = $184,250.
- Adjusted wages for the income tax comparison = $200,000 − $10,000 contribution = $190,000, so taxable income after the contribution = $190,000 − $15,750 = $174,250.
- Both taxable income amounts remain in the 24% layer. Current federal income tax savings = $10,000 × 24% = $2,400.
- Employee payroll tax uses $200,000 of wages in both calculations, so payroll tax savings = $0 and modeled total current federal savings = $2,400 + $0 = $2,400.
Result
The final 2025 comparison shows federal income tax falling from $37,067 to $34,667, a $2,400 difference. It makes no finding about whether the employee may contribute $10,000 or whether another contribution changes the annual limit.
What is included
- Federal income tax before and after the entered traditional contribution, using the selected year and filing status.
- Employee Social Security and Medicare tax on unchanged payroll wages, so payroll treatment remains visible.
- The entered contribution and the resulting current federal tax difference.
What is not included
- Plan participation, annual limit coordination, catch up qualification, employer matching, vesting, and excess deferral correction.
- Roth contributions, future distributions, investment growth, required minimum distributions, penalties, and state or local tax.
- A recommendation to contribute and any claim that the entered amount is allowed under a particular workplace plan.
Common mistakes
Subtracting the deferral from payroll wages
Traditional 401(k) deferrals generally remain wages for Social Security and Medicare. Treating the contribution as exempt from both income and payroll tax overstates the current result. The comparison intentionally holds payroll wages constant.
Reading the IRS maximum as a personal allowance
The published ceiling is not an eligibility determination. Age, plan terms, compensation, other elective deferrals, and payroll processing all matter. Confirm the available amount with the plan administrator and payroll records.
Calling tax deferral permanent savings
The $2,400 example measures current federal income tax only. Traditional distributions can be taxable later. A lifetime comparison would need future withdrawals, rates, returns, fees, and timing that are not entered here.
Frequently asked questions
What does the 401(k) tax savings calculator compare?
It compares supported federal income tax before and after a traditional 401(k) contribution while holding payroll wages constant.
Do traditional 401(k) contributions reduce FICA tax?
Generally no. Traditional employee deferrals can reduce federal taxable income but usually remain subject to Social Security and Medicare tax.
Does this calculator determine my contribution limit?
No. Plan terms, age, compensation, employer contributions, and federal annual limits can affect the amount permitted. Enter a contribution you have separately validated.
Primary sources
- IRS Publication 15 (Circular E), Employer's Tax Guide for 2025, opens in a new tab
Reviewed 2026-07-25
- 2025 Instructions for Form 1040, opens in a new tab
Reviewed 2026-07-25
- IRS Revenue Procedure 2025-32, opens in a new tab
Reviewed 2026-07-25
- IRS Notice 2024-80, opens in a new tab
Reviewed 2026-07-25
- IRS Notice 2025-67, opens in a new tab
Reviewed 2026-07-25