Pre-tax deductions (401k, HSA) and your paycheck

Some of the most valuable money on a US paycheck is the money you never get taxed on. Pre-tax deductions — chiefly the 401(k), the HSA and the FSA — come out of your pay before income tax is calculated, lowering your taxable income and your tax bill in the same move. This guide explains how each one works and which also dodge FICA.

The traditional 401(k)

A traditional 401(k) is the workhorse. Contributions are deducted from your gross pay before federal (and usually state) income tax, so a dollar contributed costs you less than a dollar of take-home. For 2025 you can contribute up to $23,500 (with an extra catch-up amount if you are 50 or older). The trade-off is that you pay income tax when you withdraw in retirement — the deferral, not avoidance, is the point. Note that 401(k) contributions reduce income tax but not FICA: Social Security and Medicare are still charged on the full amount.

The HSA: the triple tax advantage

If you are on a qualifying high-deductible health plan, a Health Savings Account is arguably the most tax-efficient account in the US system. Contributions are pre-tax, the money grows tax-free, and qualified medical withdrawals are tax-free too — the so-called triple tax advantage. For 2025 the limits are $4,300 (self-only) and $8,550 (family). And when contributed through your employer’s payroll, HSA money usually escapes FICA as well, which a 401(k) does not.

FSAs and other pre-tax items

A Flexible Spending Account (FSA) also uses pre-tax dollars for medical or dependent-care costs, but it is mostly “use it or lose it” within the plan year, so you fund it to your expected spend rather than as long-term savings. Employer-sponsored health, dental and vision premiums are commonly pre-tax too, as are commuter benefits in some plans.

Why this matters for take-home

Because these deductions shrink your taxable income, they can quietly move you into a lower federal bracket and reduce the tax on every remaining dollar. The headline effect feels backwards at first: contributing more to your 401(k) lowers this month’s take-home, but by less than the amount contributed — the government effectively funds part of your savings. Try adding a pre-tax contribution on the US take-home pay calculator to see the real cash-flow effect for your salary.

The takeaways

Pre-tax accounts are the main legal lever over US take-home pay: the 401(k) defers income tax, the HSA avoids it entirely (and usually FICA too), and FSAs cover near-term costs tax-free. For the taxes these deductions reduce, read US payroll taxes explained. Limits and eligibility are individual and change annually — confirm the current figures before you set your contributions.