The quick answer
Maxing a pretax 401(k) at $24,500 reduces your federal taxable income by $24,500. The actual tax savings is $24,500 × your top marginal rate. Not your effective rate — the top bracket your last dollar falls into.
By 2026 bracket (single filer)
| Bracket | Income where it starts | Tax saved on $24,500 |
|---|---|---|
| 10% | $0 | $2,450 |
| 12% | $11,925 | $2,940 |
| 22% | $48,475 | $5,390 |
| 24% | $103,350 | $5,880 |
| 32% | $197,300 | $7,840 |
| 35% | $250,525 | $8,575 |
| 37% | $626,350 | $9,065 |
That table assumes your entire $24,500 contribution comes out of income above the bracket boundary. For most workers in the middle brackets, part of the contribution would span two brackets; the savings are slightly lower than the table suggests.
The effective rate gotcha
If your household effective rate is 13% but you're still in the 22% marginal bracket, the contribution saves you 22% today. It does not save you 13%. The deduction is carved off the top, not smeared across the average. This is the single most misunderstood point about 401(k) math.
State tax on top
Most states mirror the federal treatment, meaning your $24,500 also escapes state tax. In California at 9.3%, that's another $2,280 saved. In Texas or Florida, it's $0. Factor your state in before deciding between Roth and pretax.
Don't forget FICA
Pretax 401(k) contributions still pay Social Security and Medicare tax. So the *gross* tax savings is only federal (and state) income tax, not payroll tax. HSA contributions through payroll are the exception — they escape FICA too, which is why the HSA is the most tax-advantaged account in America.
Want to run your own number? Use our calculator above and plug in your exact salary and bracket.