Traditional 401(k) deferrals reduce federal taxable wages today in exchange for retirement savings tomorrow. Each dollar deferred typically costs less than a dollar of net pay because you skip federal and often state income tax on that slice — but FICA still applies to traditional deferrals. Understanding that gap helps you increase savings without guessing how much your checking account will shrink.
This guide compares pre-tax vs. Roth paycheck impact, walks a $500/month deferral example, explains 2026 IRS limits, and shows how to ramp deferrals sustainably. Model changes in PaycheckScope's salary-after-tax calculator after each adjustment.
Pre-Tax vs. Roth: Paycheck Difference
Traditional deferrals lower current taxable wages; you pay tax on qualified withdrawals later. Roth deferrals use after-tax dollars — same gross, lower net today, but qualified withdrawals are tax-free in retirement. The better choice depends on whether your marginal rate is higher now or later, not on gut feeling.
Employer match is usually pre-tax regardless of your Roth election on employee deferrals. Match formulas are described in your Summary Plan Description.
$500/Month Traditional 401(k) Example
$72,000 salary, single filer, ~22% federal marginal, ~5.5% state illustrative, FICA still on full gross:
- Without deferral: net ≈ $4,650/month
- With $500/month traditional deferral: federal/state savings ≈ $135/month combined
- Net ≈ $4,515/month — deferral "costs" ~$365 net, not $500
At higher marginal rates, the net cost per deferred dollar falls further. Near zero marginal rate years, Roth may dominate.
Employer Match: Free Money Math
50% match on first 6% of salary = 3% of compensation if you contribute 6%. On $72,000, contributing 6% ($4,320) captures $2,160/year employer money. Skipping match to keep net pay is usually leaving a guaranteed return on the table — prioritize match before extra deferrals beyond the match threshold.
Vesting schedules matter: immediate vesting beats higher match that cliffs at three years if you might leave. Discount unvested match in offer comparisons.
Contribution Limits in 2026
IRS elective deferral limit: $24,500 for employees under 50. Catch-up contribution: $8,000 for age 50+. Enhanced catch-up for ages 60–63: $11,250 under current law. Hitting the max early stops deferrals mid-year and can raise net pay temporarily — plan cash flow if you front-load.
Total annual additions (employee + employer) face a separate section 415(c) limit — high earners with mega backdoor strategies should confirm with plan administrator.
Finding Your Sustainable Deferral Rate
- Secure employer match at minimum.
- Increase deferral 1% per quarter until net pay hits your monthly floor.
- Re-run calculator after each raise — lifestyle creep competes with deferrals.
- Pair with emergency fund so you do not pause deferrals after one surprise bill.
Tax Diversification: Roth, Traditional, and Taxable
Splitting deferrals between traditional and Roth accounts spreads risk across future tax rates. Early-career workers in lower brackets sometimes favor Roth; peak earners often favor traditional to reduce current marginal tax. There is no universal answer — model your marginal rate today vs. expected rate at withdrawal.
Employer match is almost always pre-tax; heavy Roth employee deferrals still leave a tax-deferred match bucket in retirement.
After-Tax Paycheck Math at $100,000 Gross
Single filer, no deferrals: net might land near $74,000 after federal, FICA, and a 5% illustrative state. Adding $12,000 traditional deferral ($1,000/month) reduces taxable wages — federal and state savings might total ~$2,400/year while FICA stays on full gross. Net might fall only ~$9,600 annually (~$800/month) while retirement savings rise $12,000. That 67% "discount" on deferral is why maxing tax-advantaged accounts is often cheaper than it appears on the first calculator pass.
Loans, Hardship Withdrawals, and Auto-Escalation
401(k) loans repay with after-tax dollars through payroll — interest returns to your account, but you lose market growth on borrowed amounts. Hardship withdrawals (where permitted) trigger income tax and often a 10% early withdrawal penalty under age 59½ unless an exception applies. Model net pay before cutting deferrals to cover emergencies — sometimes a smaller deferral beats a taxable withdrawal.
Auto-escalation (increase deferral 1% each year) pairs well with raise season: net pay may stay flat while savings climb. Pause escalation if you expect a mortgage or childcare spike the same year.
After reaching the annual deferral limit mid-year, net pay jumps — redirect that temporary surplus to Roth IRA or taxable brokerage if your plan allows, rather than lifestyle inflation that is hard to reverse when deferrals restart January 1.
Frequently Asked Questions
Does 401(k) reduce FICA?
Traditional deferrals reduce federal income tax withholding but not employee FICA on those dollars. Some cafeteria plans treat HSA differently.
Can I change deferral mid-year?
Most plans allow per-paycheck changes; payroll cutoffs vary.
Roth or traditional at 22% marginal?
Depends on expected retirement marginal rate and time horizon — not just current bracket.
What if I over-defer and hit the limit in October?
Payroll stops deferrals; net pay rises. Ensure you did not exceed catch-up eligibility incorrectly.
Where do I see net impact before enrolling?
Use the salary-after-tax calculator with and without planned deferral dollars.
Disclaimer: This article is for educational purposes only and is not tax, legal, or financial advice. Tax rules change by year, state, and individual circumstances. Confirm figures with official IRS and state revenue publications or a qualified tax professional before making withholding, relocation, or investment decisions.