A pre-tax deduction is money taken from an employee's gross pay before taxes are calculated, which lowers the wages subject to tax. Health insurance premiums through a Section 125 plan, traditional 401(k) deferrals, HSA contributions, and FSA contributions are the most common examples.
Key takeaways
- Pre-tax deductions reduce taxable wages, so employees pay less tax on the same gross pay.
- Not every pre-tax deduction escapes every tax: traditional 401(k) deferrals still owe FICA.
- Employers save too, because their FICA match is lower when Section 125 deductions reduce FICA wages.
- Roth 401(k) contributions and most voluntary insurance are after-tax deductions.
How pre-tax deduction works
Payroll applies deductions in order. Pre-tax deductions come out first, then taxes are calculated on what remains, then after-tax deductions are taken. Which taxes a pre-tax deduction avoids depends on the tax code section behind it (IRS Publication 15-B, Employer's Tax Guide to Fringe Benefits).
| Deduction | Federal income tax | FICA |
|---|---|---|
| Section 125 medical, dental, vision premiums | Exempt | Exempt |
| Health FSA and dependent care FSA | Exempt | Exempt |
| HSA through a cafeteria plan | Exempt | Exempt |
| Traditional 401(k) or 403(b) deferral | Exempt | Taxable |
| Qualified transit and parking | Exempt | Exempt |
State treatment usually follows federal rules, with exceptions. Pennsylvania, for example, taxes 401(k) deferrals for state income tax, and New Jersey taxes them for some state purposes.
Pre-tax deduction example
An employee earning $4,000 a month pays $250 in medical premiums through a cafeteria plan. Without the Section 125 plan, the full $4,000 would be subject to FICA. With it, FICA applies to $3,750. The employee saves $19.13 a month in FICA and, at a 22% federal bracket, $55 in federal income tax. The employer also saves $19.13 a month in its FICA match, or about $230 a year per participating employee.
Multiply that across 200 participants and the employer saves roughly $46,000 a year, which often pays for the plan's administration several times over.
Why pre-tax deduction matters for employers
Pre-tax benefits are one of the few ways to raise take-home pay without raising salary. With average family premium contributions by workers at $6,850 a year in 2025 (KFF 2025 Employer Health Benefits Survey), running premiums pre-tax is worth hundreds of dollars a year to a typical family.
Setup is where errors creep in. A Section 125 premium-only plan needs a written plan document; without one, premiums are technically taxable. Payroll codes must be mapped to the right tax treatment for every tax type. A wrong setting can understate FICA for years before anyone notices, usually when W-2 box 3 doesn't reconcile.
Common pre-tax deduction mistakes to avoid
Running premiums pre-tax without a plan document
A Section 125 cafeteria plan requires a written document. Without one, the exclusion can be challenged.
Exempting 401(k) deferrals from FICA
Traditional deferrals reduce income tax wages only.
Ignoring state differences
A few states don't follow federal treatment for retirement deferrals.
Letting employees change elections anytime
Section 125 elections are generally locked for the plan year unless a qualifying life event occurs.
Pre-tax deduction: questions people also ask
What are examples of pre-tax deductions?
Are pre-tax deductions better than post-tax deductions?
Do pre-tax deductions reduce Social Security benefits?
Is life insurance a pre-tax deduction?
Can an employee change pre-tax elections mid-year?
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HRTally glossary entries are written by people who have run US payroll, benefits, and HR operations, then checked line by line against primary sources such as the IRS, Department of Labor, EEOC, and Bureau of Labor Statistics. Dollar limits and rates are for 2026 unless stated. We review every entry at least twice a year and whenever a rule changes. This page explains general rules and isn't legal or tax advice; state law can differ. Read our editorial standards.
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<blockquote>A pre-tax deduction is money taken from an employee's gross pay before taxes are calculated, which lowers the wages subject to tax. Health insurance premiums through a Section 125 plan, traditional 401(k) deferrals, HSA contributions, and FSA contributions are the most common examples.</blockquote><p>Source: <a href="https://www.hrtally.com/hr-glossary/pre-tax-deduction/">HRTally HR Glossary, Pre-tax deduction</a></p>
Written by the HRTally Research Team
Our guides are written and reviewed by people with hands-on US HR, payroll, and HR technology experience. Legal and tax facts are checked against primary sources, such as the Department of Labor, IRS, EEOC, and USCIS, and linked at the end of each guide. Vendors never review or pay for our editorial content.