What a 401(k) Contribution Actually Costs You Per Paycheck
Putting $6,000 a year into a traditional 401(k) does not reduce your take-home pay by $6,000. It reduces it by less, because that money never enters your taxable income — so part of what you contributed would have gone to the government anyway.
How much less depends entirely on your marginal bracket and your state. The gap is the single most under-appreciated number in retirement saving.
What it actually costs
| Scenario | Gross | Take-home drop | Tax avoided | Effectively free |
|---|---|---|---|---|
| $25/hr — Texas (no income tax) | $52,000 | $4,821 | $1,179 | 20% |
| $25/hr — California | $52,000 | $4,484 | $1,516 | 25% |
| $50/hr — Texas (no income tax) | $104,000 | $4,221 | $1,779 | 30% |
| $50/hr — California | $104,000 | $3,663 | $2,337 | 39% |
| $75/hr — New York | $156,000 | $3,747 | $2,253 | 38% |
Read the California row at $50/hr. Contributing $6,000 costs $3,663 of take-home pay. The remaining $2,337 is tax you did not pay. The money still left your paycheck — but it went into an account with your name on it rather than to the IRS and the Franchise Tax Board.
Why the saving is bigger in high-tax states
A 401(k) deduction reduces both your federal and your state taxable income. In a state with no income tax, only the federal saving applies. In California or New York, you avoid both — so the same contribution costs noticeably less out of pocket.
This is one of the few places where living in a high-tax state works in your favour: the more heavily your marginal dollar is taxed, the more a pre-tax contribution is worth.
FICA is the exception
Traditional 401(k) contributions reduce income tax but not Social Security and Medicare. You pay FICA on your full salary regardless of what you defer. That is why the tax avoided in the table above is smaller than your marginal rate alone would suggest.
HSA contributions made through an employer plan are different — they typically escape FICA as well as income tax, which makes them the most tax-efficient dollar available to most workers.
The employer match is separate, and larger
Everything above concerns the tax treatment. If your employer matches contributions, that match dwarfs the tax saving. A 50% match on the first 6% of salary is an immediate 50% return on those dollars — nothing in the tax code comes close.
The practical order for most people: contribute enough to capture the full match first, then weigh additional pre-tax contributions against other goals.
Traditional vs Roth in one line
Traditional defers tax to retirement; Roth pays it now and withdraws tax-free later. The arithmetic turns on whether your marginal rate in retirement will be higher or lower than today. Everything in this guide describes traditional contributions — Roth contributions are made after tax and will not reduce your take-home pay calculation at all.
Run your own
The calculator has a 401(k) field under Advanced Options. Enter your annual contribution and watch the take-home figure move by less than the amount you entered — the difference is the tax you avoided. Start with $50/hr in California, or read where the rest of your paycheck goes.