Pre-Tax vs Post-Tax Paycheck Deductions
Are health insurance premiums pre-tax? Through a cafeteria plan they skip income tax and FICA. A 401(k) skips only income tax. A 2026 example shows the gap.
Are health insurance premiums pre-tax? If your employer takes them out through a Section 125 cafeteria plan, which is how most employer health plans collect them, yes. They come out before federal income tax and before Social Security and Medicare. A traditional 401(k) works differently. It skips federal income tax, but you still pay Social Security and Medicare on every dollar you put in.
So two deductions of the same size can cost you different amounts. A dollar of health premium saves you more tax than a dollar of 401(k) deferral, and a Roth 401(k) dollar saves you nothing this year.
Three groups of paycheck deductions
Every line on your pay stub falls into one of three groups.
Before income tax and FICA. Your employer subtracts these before it works out federal income tax withholding, Social Security (6.2%) and Medicare (1.45%). Section 125 health, dental and vision premiums, HSA contributions made through payroll and health FSA contributions sit here.
Before income tax only. Traditional 401(k) and 403(b) deferrals lower the wages your federal income tax is figured on. Social Security and Medicare still apply to the full amount. IRS Publication 15 lists elective 401(k) deferrals as generally exempt from income tax withholding and taxable for Social Security and Medicare.
After tax. Roth 401(k) contributions, premiums your employer deducts after tax, union dues, payroll charity gifts and wage garnishments all come out of pay that has already been taxed. They lower your take-home pay without lowering your tax.
Which deductions are pre-tax
| Deduction | Federal income tax | Social Security and Medicare |
|---|---|---|
| Health, dental and vision premiums through a Section 125 cafeteria plan | Excluded | Excluded |
| HSA contributions through a cafeteria plan (2026 limit $4,400 self-only, $8,750 family) | Excluded | Excluded |
| Health FSA contributions (2026 limit $3,400) | Excluded | Excluded |
| Traditional 401(k) and 403(b) deferrals | Excluded | Taxed |
| Roth 401(k) and Roth 403(b) contributions | Taxed | Taxed |
| Premiums your employer deducts after tax | Taxed | Taxed |
| Wage garnishments, union dues, payroll charity gifts | Taxed | Taxed |
The cafeteria plan rules, the HSA treatment and the $3,400 health FSA cap come from IRS Publication 15-B for 2026. The 401(k) treatment comes from IRS Publication 15 for 2026.
One HSA detail catches people out. If you put money into an HSA on your own and claim the deduction on your tax return, you get the income tax break, but the Social Security and Medicare you already paid on that money stays paid. Through payroll, you never pay it. The HSA guide covers the rest of the account's tax treatment.
A 2026 paycheck, worked through
Take a single filer earning $75,000 a year, paid monthly ($6,250 a month). She puts 6% into a traditional 401(k), which is $375 a month or $4,500 a year. Her health premium is $200 a month through a cafeteria plan, $2,400 a year. She lives in Texas, so there is no state income tax.
Federal income tax. Both deductions come off before the standard deduction. Taxable income is $75,000 − $4,500 − $2,400 − $16,100 = $52,000. Using the 2026 single brackets, that is 10% of $12,400 ($1,240), plus 12% of the next $38,000 ($4,560), plus 22% of the last $1,600 ($352). Federal tax is $6,152.
Social Security and Medicare. Only the health premium comes off here. FICA wages are $75,000 − $2,400 = $72,600. Social Security is 6.2% of that, $4,501.20. Medicare is 1.45%, $1,052.70.
Take-home pay. $75,000 − $6,152 − $4,501.20 − $1,052.70 − $4,500 − $2,400 = $56,394.10 a year, or $4,699.51 a month.
Now move both deductions after tax. She switches to a Roth 401(k) at the same 6% and pays the same premium with taxed money. Taxable income rises to $58,900 and federal tax to $7,670. FICA wages go back to the full $75,000, so Social Security is $4,650 and Medicare $1,087.50. After the $6,900 of deductions she takes home $54,692.50, or $4,557.71 a month.
Same deductions, $141.80 less every month. Here is where the $1,701.60 a year comes from:
| Federal income tax saved | Social Security and Medicare saved | Total | |
|---|---|---|---|
| $4,500 traditional 401(k) | $990.00 | $0 | $990.00 |
| $2,400 Section 125 premium | $528.00 | $183.60 | $711.60 |
| Both | $1,518.00 | $183.60 | $1,701.60 |
Each 401(k) dollar saved her 22 cents, her federal bracket. Each premium dollar saved 29.65 cents, because the 7.65% of FICA comes off as well. A Roth still has its own case: you pay the tax now and qualified withdrawals come out tax-free later. The 2026 401(k) limits article compares the two.
You can reproduce these numbers in the take-home paycheck calculator. Enter $6,250 as monthly gross pay, choose Single, put 6 in the 401(k) field, 200 in the pre-tax health insurance field and 0 as the state rate. It shows $4,699.51 as monthly take-home pay, with $6,152 federal tax, $4,501.20 Social Security and $1,052.70 Medicare for the year. Set both deductions to 0 and you get $5,132.71, the starting point for the after-tax version above. The calculator has no separate HSA field. Payroll HSA money gets the same treatment as the health premium, so you can add it to that field.
The calculator estimates a full year of tax. Your employer's actual withholding follows your W-4 and the IRS withholding tables, so a single paycheck can be a few dollars off. The 2026 tax brackets article explains how this year's bracket changes move that number.
Higher earners: the wage base and Additional Medicare Tax
Social Security only applies to the first $184,500 of wages in 2026, according to the Social Security Administration's 2026 fact sheet. If your FICA wages are above that even after your premiums come out, a cafeteria plan premium no longer saves you the 6.2%. It still saves 1.45% Medicare.
At the other end, your employer withholds an extra 0.9% Additional Medicare Tax on wages above $200,000 a year. Section 125 premiums lower those Medicare wages too, so above $200,000 each premium dollar saves 2.35% in Medicare tax instead of 1.45%. The take-home paycheck calculator includes both rules.
How to check your own pay stub
Your W-2 shows the split. Box 1 is wages for federal income tax, after both 401(k) deferrals and Section 125 deductions. Boxes 3 and 5 are Social Security and Medicare wages, which only lose the Section 125 deductions. If Box 1 is lower than Box 5, the gap is mostly your traditional 401(k) or 403(b) money.
On a pay stub, look at how each deduction is labelled. Many payroll systems mark pre-tax deductions with "pre-tax" or "Sec 125". If your health premium sits in the after-tax section, ask HR whether the plan has a cafeteria plan document. Without one, the premium can't come out pre-tax.
State income tax doesn't always follow
Most states with an income tax start from federal wages, so the same deductions usually lower your state tax as well. Some states make their own rules. Two well-documented exceptions:
- Pennsylvania taxes employee contributions to 401(k) and other retirement plans as compensation, according to the Pennsylvania Department of Revenue. Your 401(k) lowers your federal tax but not your 3.07% state tax.
- California doesn't recognize HSAs, so HSA contributions made through payroll count as taxable income for California, per the Franchise Tax Board's Schedule CA instructions.
The calculator subtracts both pre-tax deductions before applying your state rate. In Pennsylvania that understates state tax by 3.07% of your 401(k) deferral, and in California it understates state tax on any HSA money you add to the health field. Local wage taxes have their own rules again. Check your state's revenue department before relying on any one figure.
This article is general information about how US payroll deductions are taxed. It is not tax advice for your situation, and plan rules vary by employer.