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How pre-tax payroll deductions work
A pre-tax deduction is an amount withheld from an employee's gross wages before payroll taxes are calculated, which lowers their taxable income and reduces what both of you owe. Which taxes it reduces depends on the benefit. Health insurance under a Section 125 plan comes out before income tax and FICA. A traditional 401(k) comes out before income tax but still owes Social Security and Medicare.
That second point is where most of the confusion lives, and getting it backwards means either over-withholding from your employees or underpaying the IRS.
Key Takeaways from this Article
- Pre-tax deductions come out of gross wages before taxes. Post-tax deductions come out after.
- Not all pre-tax deductions reduce the same taxes, and the difference matters on every paycheck.
- Retirement contributions reduce income tax but not Social Security and Medicare.
- Health and dependent care benefits only escape FICA if you have a Section 125 plan in place.
- Garnishments, union dues, and most voluntary repayments are post-tax, and they can't take an employee below minimum wage.
What is a Pre-Tax Deduction?
A pre-tax deduction is money withheld from an employee's pay before taxes are figured. The employee's taxable wages drop by that amount, so they pay less tax, and depending on the benefit, you pay less employer tax too.
Say someone earns $1,000 a pay period and puts $100 toward health insurance through a Section 125 plan. Taxes get calculated on $900, not $1,000. The employee keeps more of their pay than they would have by buying the same coverage on their own, and your share of FICA drops as well.
What is the Difference Between Pre-Tax and Post-Tax Deductions?
Timing, and what it costs.
| Pre-tax | Post-tax | |
|---|---|---|
| Taken from | Gross wages, before tax | Net wages, after tax |
| Reduces taxable income | Yes | No |
| Employer saves payroll tax | Sometimes | No |
| Employee chooses | Usually, during enrollment | Sometimes, or court ordered |
| Typical examples | Health premiums, 401(k), FSA | Roth 401(k), garnishments, union dues |
Run the same $1,000 paycheck through both. Pre-tax: $100 for health insurance comes out first, taxes apply to $900. Post-tax: taxes apply to the full $1,000, then $50 goes to a charitable donation from what's left.
Post-tax deductions aren't worse, they're just for things that don't qualify. A Roth 401(k) is post-tax on purpose, because the tax break comes later instead of now.
Which Taxes Do Pre-Tax Deductions Reduce?
This is the part that trips people up, because "pre-tax" doesn't mean exempt from everything. Each benefit has its own treatment.
| Deduction | Federal income tax | Social Security and Medicare | FUTA |
|---|---|---|---|
| Health, dental, vision premiums (Section 125) | Exempt | Exempt | Exempt |
| HSA contributions (Section 125) | Exempt | Exempt | Exempt |
| FSA contributions (Section 125) | Exempt | Exempt | Exempt |
| Dependent care assistance | Exempt | Exempt | Exempt |
| Commuter and parking benefits | Exempt | Exempt | Exempt |
| Traditional 401(k) or 403(b) | Exempt | Subject | Subject |
| Roth 401(k) | Subject | Subject | Subject |
The retirement row is the one to remember. Your employee's 401(k) contribution lowers their income tax withholding but not their Social Security and Medicare, and it doesn't lower your employer match on those either. People assume a pre-tax retirement contribution saves FICA. It doesn't.
The other thing worth flagging: those health and dependent care exemptions depend on having a Section 125 cafeteria plan in place, with a proper written plan document. Deducting health premiums pre-tax without one is a fairly common mistake, and it means the FICA savings you thought you were getting aren't real.
State treatment generally follows the federal pattern but not always, so check your own state's rules if you operate outside Maine. The IRS covers every category in Publication 15-B.
What Are Examples of Pre-Tax Deductions?
The common ones, in rough order of how often they show up on a small business payroll:
- Health, dental, and vision premiums, through a Section 125 plan
- Traditional 401(k) and 403(b) contributions
- Health Savings Account contributions, paired with a high deductible plan
- Flexible Spending Account contributions for healthcare or dependent care
- Dependent care assistance
- Commuter benefits for transit and parking, up to the monthly IRS limit
- Group term life insurance premiums, for coverage up to $50,000
Group term life deserves a footnote. Coverage up to $50,000 is fine, but anything above that becomes taxable income to the employee, calculated from an IRS age-based table rather than what the policy actually costs.
What Deductions Are Not Pre-Tax?
Plenty of what comes out of a paycheck doesn't qualify. Wage garnishments, child support orders, union dues, uniform costs, tool repayments, employee cash advances, and charitable contributions all come out after tax.
Two rules apply to most of these. They generally need the employee's written authorization, and they can't reduce someone's pay below minimum wage for the hours they worked. Court-ordered garnishments are the exception to the first rule but have their own limits on how much can be taken.
FAQs: Pre-Tax Payroll Deductions
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A pre-tax deduction is an amount taken from an employee's gross wages before payroll taxes are calculated. It lowers their taxable income, so they owe less tax, and for many benefits it lowers the employer's payroll tax as well. Health insurance premiums, 401(k) contributions, and FSA contributions are the most common examples.
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Pre-tax deductions come out of gross wages before taxes are figured, which reduces taxable income. Post-tax deductions come out of what's left after taxes, so they don't affect the tax calculation at all. A traditional 401(k) is pre-tax and a Roth 401(k) is post-tax, which is the clearest illustration of the difference: same account type, opposite tax timing.
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Some are, some aren't. Health, dental, and vision premiums, HSA and FSA contributions, dependent care assistance, and commuter benefits are exempt from Social Security and Medicare, provided you have a Section 125 plan in place. Traditional 401(k) and 403(b) contributions are not. Those reduce income tax withholding only, and FICA still applies to the full amount.
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Traditional 401(k) and 403(b) contributions are pre-tax for income tax purposes but still subject to Social Security and Medicare. Roth contributions are post-tax throughout. If you're looking at a pension or a plan you're unsure about, check whether contributions are designated Roth, since that's what decides it.
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No. Garnishments are post-tax, withheld from wages after all taxes have been calculated. That applies to child support, tax levies, and creditor garnishments alike. Federal and state rules cap how much of someone's disposable earnings can be taken, and those caps are calculated from pay after taxes rather than gross.
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Health, dental, and vision premiums through a Section 125 plan, traditional 401(k) and 403(b) contributions, HSA and FSA contributions, dependent care assistance, commuter and parking benefits up to the IRS monthly limit, and group term life insurance premiums for coverage up to $50,000.
Getting the Setup Right
Most pre-tax problems trace back to setup rather than processing. A deduction coded to the wrong tax treatment doesn't announce itself. It just quietly produces slightly wrong withholding on every check until someone reconciles a W-2 in January and can't make the numbers work.
The two we see most often are health premiums running pre-tax without a Section 125 document behind them, and 401(k) contributions coded to skip FICA. Both are easy to fix going forward and tedious to fix backward.
We handle deduction setup as part of payroll and tax, and if you want to see what the deductions are doing to an actual paycheck, our breakdown of gross pay versus net pay walks through the whole calculation.
Updated: September 2026
Written by: Jon Portanova
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