Withholding & Planning · 2025
Pre-Tax Contribution Tax Savings Calculator
Enter your income and a 401(k), HSA, Traditional IRA, or SEP-IRA contribution amount to see your exact federal tax savings — including FICA savings for contributions that reduce payroll taxes — and the true net cost of the contribution after all savings are applied.
Your information
Before contributions or deductions
$23,500 (under 50) · $31,000 (50+) · $34,750 (60–63)
Employee elective deferral. Reduces federal and FICA taxable wages.
Informational only — not professional tax advice.
Enter your income and contribution amount to see your exact federal tax savings — and FICA savings if the contribution type reduces payroll taxes.
Methodology
How tax savings are computed
The calculator calls the federal tax computation engine twice — once at your full gross income and once at gross income minus the contribution amount — and takes the difference. That delta is your federal income tax savings. For contribution types that reduce FICA wages (Traditional 401(k)/403(b) and HSA), the same delta approach is applied to Social Security and Medicare taxes. For IRA and SEP-IRA contributions, which are deducted on Form 1040 rather than excluded from FICA wages, only the income tax savings is computed.
Formula
Federal income tax savings: federal_before = computeFederalTax(grossIncome, filingStatus, standardDeduction) federal_after = computeFederalTax(grossIncome − contribution, filingStatus, standardDeduction) federal_savings = federal_before.totalTax − federal_after.totalTax FICA savings (401k and HSA only — not IRA/SEP-IRA): fica_before = SS tax + Medicare tax on grossIncome fica_after = SS tax + Medicare tax on (grossIncome − contribution) fica_savings = fica_before.total − fica_after.total Total savings = federal_savings + fica_savings Net cost = contribution − total_savings Discount rate = total_savings ÷ contribution
2025 contribution limits
| Account | 2025 Limit | Catch-up | Source |
|---|---|---|---|
| Traditional 401(k) / 403(b) | $23,500 | $31,000 (50+) · $34,750 (60–63) | IRS Notice 2024-80 |
| HSA (self-only HDHP) | $4,300 | +$1,000 (age 55+) | IRS Rev. Proc. 2024-25 |
| HSA (family HDHP) | $8,550 | +$1,000 (age 55+) | IRS Rev. Proc. 2024-25 |
| Traditional IRA | $7,000 | $8,000 (50+) | IRS Pub 590-A |
| SEP-IRA | $70,000 max (25% of comp.) | — | IRS Notice 2024-80 |
Stated assumptions and limitations
- Standard deduction assumed. Federal tax savings uses the 2025 standard deduction for your filing status. If you itemize, your actual savings may differ.
- IRA deductibility phase-out not applied. The calculator assumes full Traditional IRA deductibility. For 2025, phase-outs begin at $79,000 MAGI (single, covered by a workplace plan) and $126,000 (MFJ). Above those thresholds, IRA deductibility is reduced or eliminated, and actual savings will be less than shown.
- No state income tax savings. Many states also allow deductions for these contributions. Actual total savings including state income tax will be higher than shown here.
- FICA savings shown are employee share only. Employers also save their matching 7.65% FICA on excluded wages — that saving belongs to your employer, not to you.
Last reviewed: January 2025. Contribution limits are set annually by IRS inflation adjustments published in October/November (Notice 2024-80 for plan year 2025). HSA limits are announced separately in spring (Rev. Proc. 2024-25).
Frequently asked questions
Does a 401(k) contribution reduce my Social Security and Medicare taxes too?
Yes — employee elective deferrals to a Traditional 401(k) or 403(b) reduce your FICA (Social Security and Medicare) taxable wages. Because those contributions are excluded from W-2 Box 3 (Social Security wages) and Box 5 (Medicare wages), your employer withholds less SS and Medicare tax. At a combined employee FICA rate of 7.65% (6.2% SS + 1.45% Medicare), a $10,000 contribution saves an additional $765 in FICA taxes on top of the federal income tax savings. IRA contributions do not reduce FICA — they are a deduction on Form 1040, not an exclusion from FICA wages.
Is the HSA tax savings better than a 401(k)?
An HSA is often the best tax vehicle available when you're eligible. Contributions reduce both federal income tax and FICA wages (same as a 401(k)), the money grows tax-free, and qualified medical withdrawals are never taxed — a triple tax benefit no other account matches. The trade-off is the HDHP enrollment requirement and the annual contribution limit ($4,300 self-only, $8,550 family for 2025). A 401(k) has a much higher contribution limit ($23,500, or $31,000 if 50+) and no HDHP requirement. If you have access to both, maxing the HSA first is often the highest-return move.
Why do IRA contributions save less than 401(k) contributions at the same income?
The key difference: IRA contributions reduce your federal income tax through a Form 1040 deduction but do not reduce your FICA (Social Security and Medicare) taxable wages. 401(k) contributions are excluded from FICA wages before the W-2 is even issued, so they save both income tax and payroll tax. Also, Traditional IRA deductibility phases out for single filers with workplace retirement plan coverage above $79,000 MAGI (2025), and for MFJ filers above $126,000 — if you're in a phase-out range, your IRA savings will be smaller than this tool shows (it assumes full deductibility). Roth IRA contributions are never deductible.
What is the 2025 401(k) catch-up limit for people between ages 60 and 63?
SECURE 2.0, enacted in December 2022, created a new 'super catch-up' contribution limit for employees who are 60, 61, 62, or 63 years old. For 2025, employees in that age range can contribute up to $34,750 to their 401(k) or 403(b) ($23,500 base limit + $11,250 super catch-up). The regular age-50+ catch-up of $7,500 (bringing the limit to $31,000) applies to those 50-59 and 64+. This tool uses the under-50 limit by default; if you're in the catch-up range, enter your actual planned contribution amount to see the correct savings.
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