How Does a 401(k) Reduce Your Taxes?
A traditional 401(k) is a pre-tax deduction - it lowers your taxable income before federal and state taxes are calculated. If you earn $70,000 and contribute $7,000, you only pay income tax on $63,000. The 2025 limit is $23,500 (under 50) or $31,000 (age 50+).
Note: 401(k) contributions still have Social Security (6.2%) and Medicare (1.45%) applied. Health insurance premiums paid through a Section 125 plan are exempt from all payroll taxes, making them even more tax-efficient.
2025 US Federal Tax Brackets
10% up to $11,925 - 12% on $11,926-$48,475 - 22% on $48,476-$103,350 - 24% on $103,351-$197,300 - 32% on $197,301-$250,525 - 35% on $250,526-$626,350 - 37% above $626,350. Standard deduction: $15,000 (single), $30,000 (married jointly).
Frequently Asked Questions
How does a 401(k) reduce my taxes? +
Traditional 401(k) contributions reduce your taxable income dollar for dollar. If you earn $60,000 and contribute $6,000, you only pay income tax on $54,000. This lowers your federal and state income tax but not Social Security or Medicare taxes. The 2025 limit is $23,500 under 50.
Which states have no income tax? +
Nine states have no income tax in 2025: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming. Residents keep significantly more of their paycheck compared to high-tax states like California (9.3%) or New Jersey (10.75%).
What is marginal vs effective tax rate? +
Your marginal tax rate is the rate on your last dollar of income (e.g. 22%). Your effective tax rate is total tax divided by gross income - always lower because progressive brackets apply incrementally. This calculator shows both.
How is take-home pay calculated? +
Take-home = Gross salary minus pre-tax deductions (401k, health, HSA) minus federal income tax minus Social Security (6.2%) minus Medicare (1.45%) minus state income tax. Pre-tax deductions reduce taxable income before income tax is applied.
Why does my actual paycheck differ? +
Your paycheck may differ due to local city taxes, additional W-4 withholdings, Roth 401(k) contributions (post-tax), or employer-specific payroll calculations. This calculator provides a reliable baseline estimate based on standard federal and state rates.