401(k) Contributions vs. Take-Home Pay: The Real Tradeoff

Increasing your 401(k) contribution feels like it should cost you dollar-for-dollar on your paycheck — but because traditional 401(k) contributions are pre-tax, the real hit to your take-home pay is smaller than the percentage you chose. Here's the actual math.

Why a 401(k) contribution doesn't cost you the full amount

Traditional 401(k) contributions come out of your paycheck before federal income tax is calculated. That means every dollar you contribute lowers your taxable income by a dollar — so you're not just saving for retirement, you're also paying less tax right now.

The result: increasing your contribution by, say, $100 doesn't reduce your take-home pay by $100. It reduces it by less, because part of that $100 would have gone to federal tax anyway.

Worked example: $70,000 salary, increasing 401(k) from 5% to 10%

Single filer, biweekly pay, in the 12% federal bracket:

At 5% contribution:

  • Gross pay per paycheck: $2,692.31
  • 401(k) contribution: $134.62
  • Taxable pay: $2,557.69

At 10% contribution:

  • Gross pay per paycheck: $2,692.31
  • 401(k) contribution: $269.23
  • Taxable pay: $2,423.08

The extra $134.62 in contribution reduced taxable pay by $134.62 — but at a 12% marginal federal tax rate, about $16.15 of that would have gone to federal tax anyway. So the real hit to your take-home pay is closer to $118.47 per paycheck, not the full $134.62 — plus, FICA (Social Security and Medicare) still applies to the full gross pay either way, since 401(k) contributions don't reduce FICA wages.

The higher your tax bracket, the smaller the real cost

This tradeoff gets more favorable the higher your marginal tax bracket is. In the 22% bracket, that same $134.62 contribution only costs about $105 in real take-home pay. In the 32% bracket, it costs closer to $91.50. The tax savings scale with your bracket, which is part of why maximizing pre-tax retirement contributions is often recommended for higher earners.

Employer match: the part that's not a tradeoff at all

If your employer offers a match (commonly 50% or 100% up to a certain percentage of your salary), contributing at least enough to get the full match is close to a guaranteed return — money added to your retirement account that costs you nothing beyond your own contribution. Leaving match money on the table by contributing too little is effectively turning down part of your compensation.

Roth 401(k): the opposite tradeoff

A Roth 401(k) contribution is post-tax — it doesn't reduce your taxable income today, so it does cost you the full amount on your current paycheck. The tradeoff is that Roth withdrawals in retirement are tax-free, versus traditional 401(k) withdrawals being taxed as income later. Which is better depends on whether you expect to be in a higher or lower tax bracket in retirement.

See your exact numbers

The real take-home cost of a 401(k) contribution depends on your income, filing status, and current bracket. Use the PayGauge paycheck calculator to see exactly how adjusting your contribution percentage changes your actual paycheck.

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