Paycheck Deductions in the US: Pre-Tax vs Post-Tax Explained
Open your pay stub and you'll probably find a handful of lines you don't recall choosing. Some are required by law. Others are benefits you signed up for during onboarding, and you may not have thought about them since. Understanding them is worth the effort, because a few of these lines can lower your tax bill while others can't.
Three kinds of deductions
It helps to sort every line into one of three groups: required taxes, pre-tax deductions and post-tax deductions. The order matters. Pre-tax items come out first and shrink the pay that gets taxed. Post-tax items come out later and don't change your tax at all.
Required taxes
Federal income tax, Social Security and Medicare apply to nearly everyone, and most states add a state tax. Some cities and states also take small amounts for disability or paid family leave. We cover these in how paycheck taxes work.
Pre-tax deductions
These are the most valuable kind. Common ones include:
- Traditional 401(k) or 403(b): the 2026 employee limit is $24,500 according to the IRS. Workers 50 and older can add a catch-up of $8,000, and those aged 60 to 63 can add up to $11,250 if their plan allows it. It lowers income tax, though not Social Security or Medicare tax.
- Health, dental and vision premiums paid through the employer's plan. These usually reduce both income tax and payroll tax.
- Health Savings Account (HSA): for 2026 the IRS limits are $4,400 for self-only coverage and $8,750 for family coverage, with an extra $1,000 for people 55 and older, if you have a qualifying high-deductible plan. Employer contributions count toward the same limit.
- Flexible Spending Accounts (FSA): the health care FSA limit for 2026 is $3,400, with a maximum carryover of $680 if your plan allows it, and commuter benefits cover transit and parking costs.
These limits change almost every year, so recheck them each autumn when the IRS announces the new ones.
Post-tax deductions
These come from money that's already been taxed. Examples are Roth 401(k) contributions, union dues, charitable giving through payroll, wage garnishments (court-ordered withholding for debts such as child support), and some supplemental insurance. The benefit of a Roth is later, because qualified withdrawals in retirement are tax-free.
What a pre-tax deduction is really worth
Say you put $5,000 into a traditional 401(k). If your top federal bracket is 22%, you save $1,100 in income tax, so the actual cost to your yearly take-home is about $3,900. In the 12% bracket the same contribution saves $600, a cost of $4,400. The higher the bracket, the greater the saving. What is taxable income shows the full calculation.
An HSA funded through payroll can be even better, since it avoids income tax and payroll tax. A $4,400 contribution in the 22% bracket saves around $4,400 × 29.65% = $1,305, and withdrawals for medical costs are tax-free. People call it a triple tax advantage for that reason.
Employer contributions
Some lines on your stub aren't deducted from you at all. A 401(k) match and the employer's share of insurance may appear for information. That's extra compensation. If your employer matches 3% and you don't contribute enough to earn it, you're leaving free money on the table. See how to compare offers to value it properly.
Traditional or Roth?
Traditional means a tax break now and taxes later. Roth means taxes now and tax-free growth later. If you expect to be in a higher bracket in retirement, Roth may win. If your bracket will drop, traditional often does. Many people split between the two.
Wage garnishments
If a court or agency orders garnishment, the employer must follow it. Federal law generally limits how much of your disposable earnings can be taken for ordinary debts, commonly up to 25%, and other rules apply for child support or taxes. If you receive a garnishment notice, read it carefully and seek advice.
A real paycheck with deductions
Here's what the deductions look like on a $60,000 salary paid biweekly, with a 6% traditional 401(k) contribution ($138.46 per check) and $92.31 a check for pre-tax health insurance. The example uses 2026 rules for a single filer in a state with no income tax.
| Line | Per paycheck |
|---|---|
| Gross pay | $2,307.69 |
| 401(k), pre-tax | −$138.46 |
| Health insurance, pre-tax | −$92.31 |
| Federal income tax (estimate) | −$165.38 |
| Social Security and Medicare | −$169.48 |
| Net pay | $1,742.06 |
Compare that with the version without deductions in how to read a pay stub, where net pay was $1,938.07. Take-home is about $196 lower, but $138 of it went into the worker's own retirement account and $92 paid for health coverage. Also notice that federal tax fell from $193 to $165 and payroll tax fell because the insurance isn't subject to it.
Catch-up contributions and the new Roth rule
If you're 50 or older, you can put in extra beyond the standard limit. One change to know about: starting in 2026, if your pay from your employer in the previous year was above $150,000, your catch-up contributions must generally go into a Roth account, meaning they're taxed now instead of deducted. Lower earners keep the choice. Ask your plan administrator how your plan handles it.
Using your FSA wisely
A health FSA lets you set aside pre-tax money for medical costs, but the money is generally "use it or lose it," apart from limited carryover or grace-period rules your employer may offer. Estimate your costs conservatively: prescriptions, glasses, dental work and copays. Don't fund it based on a hopeful guess.
How to review your deductions
- Match each stub line to a benefit you chose.
- Check amounts are consistent from pay period to pay period.
- Ask HR about anything you don't recognize.
- At open enrollment, compare the total yearly cost of each plan, including deductibles, not only premiums.
- Revisit your 401(k) contribution after a raise.
Common questions
Do deductions reduce my gross pay? No. Gross pay stays the same. They reduce taxable pay and net pay.
Why is my net pay lower after open enrollment? Premium changes usually show up in the first check of the new year.
Where do I see them? How to read a pay stub shows where each type appears, and the US paycheck calculator lets you enter pre-tax deductions.
Written by Muhammad Tabish. 2026 limits verified in October 2026 against the IRS: 401(k) and IRA limits and Rev. Proc. 2025-19 for HSAs. The $3,400 health FSA limit and $680 carryover figure come from the same IRS 2026 inflation adjustments announcement. Not tax advice.