Pre-Tax vs Post-Tax Deductions on a Pay Stub (2026)
Pre-tax deductions shrink taxable wages before withholding is computed. See the correct stub order, a worked example, and which deductions escape FICA.
This article is general information, not legal or tax advice. Limits and rules change, and state law can differ from federal. Check with a qualified professional before setting payroll policy.
Two deductions, same dollar amount, sitting a few lines apart on the same stub. One of them changed the tax figures printed below it. The other one didn’t touch them.
That’s the whole distinction, and it’s why the labels on a stub aren’t cosmetic. A pre-tax line is subtracted from gross before withholding is computed, so it changes the wage base the tax numbers come from. A post-tax line is subtracted after, so it only changes what lands in the bank.
Get the category wrong and the document contradicts itself. Anyone who reads the stub with a calculator (a lender, an auditor, the employee) can catch it by subtracting.
Pre-tax vs post-tax deductions: what actually changes
Pre-tax changes the tax. Post-tax changes the take-home. Everything below is detail.
| Pre-tax deduction | Post-tax deduction | |
|---|---|---|
| Taken out | Before tax withholding is calculated | After the tax lines |
| Reduces | Taxable wages, and therefore the tax | Net pay only |
| Effect on W-2 | Lowers the wage boxes (which ones depends on the item) | No effect on any wage box |
| Typical items | Health, dental, vision premiums; FSA; HSA via payroll; traditional 401(k) | Roth 401(k); union dues; garnishments; after-tax life insurance; loan repayments |
| Employee gets | A smaller tax bill this period | A smaller paycheck this period |
Both types shrink net pay. Only one of them shrinks the number the IRS is looking at.
That’s also the answer to a question that shows up every January: why your year-end gross doesn’t match Box 1 on your W-2. The pre-tax lines came out in between. Our post on what YTD means on a pay stub walks through that gap in more detail.
The order on the stub, top to bottom
This next part matters most if you’re producing the document rather than reading it.
A pay stub has a fixed sequence, and the sequence carries meaning:
- Gross earnings (regular, overtime, bonus, tips, everything)
- Pre-tax deductions → produces the taxable wage base
- Tax withholding (federal income tax, Social Security, Medicare, state and local)
- Post-tax deductions
- Net pay
Step 2 is the load-bearing one, because it produces the number step 3 depends on. Move a 401(k) deferral down below the tax lines and you’ve implied that withholding was computed on full gross, which is not what the tax figures on the same page actually say.
The stub is then internally inconsistent, which is an arithmetic problem rather than a formatting one.
Most stub layouts don’t print the taxable wage subtotal as its own line, which is exactly why placement has to do the work. When a reader wants to check your arithmetic, the only thing telling them which base the withholding came from is where the deduction sits. Mis-ordering is a quiet cousin of the mistakes in our roundup of common pay stub errors, and it’s harder to spot because every individual number can look fine on its own.
One practical consequence: if you’re building stubs by hand in a spreadsheet, put the pre-tax block above the tax block even when the template you copied doesn’t. The template was probably designed by someone who only ever had post-tax deductions to show.
Not all pre-tax deductions are equal: the FICA split
The split inside “pre-tax” is where real money changes hands, and most write-ups mention it without ever putting a number on it.
“Pre-tax” is really two buckets, and they sit 7.65 cents on the dollar apart.
Section 125 cafeteria plan items escape federal income tax and FICA. That covers employer-sponsored health, dental, and vision premiums, health FSA contributions, dependent care FSA, group-term life within limits, and HSA contributions made through payroll. IRS Publication 15-B lists the qualified benefits. Note that some familiar pre-tax perks (transportation benefits, educational assistance) are not cafeteria plan items even though they’re excluded from wages by other rules.
Traditional retirement deferrals escape federal income tax only. A traditional 401(k), 403(b), or 457 deferral comes out before income tax withholding but stays in Social Security and Medicare wages. The IRS is explicit about this in its retirement plan contribution FAQ: W-2 Box 1 excludes pre-tax salary-reduction contributions, while Boxes 3 and 5 include all employee pre-tax, after-tax, and Roth contributions.
That single rule is why Box 1 and Box 3 differ on so many W-2s.
| Deduction | Reduces federal income tax? | Reduces Social Security / Medicare? | W-2 effect |
|---|---|---|---|
| Health, dental, vision premium (Section 125) | Yes | Yes | Lowers Box 1 and Boxes 3/5 |
| Health FSA, dependent care FSA | Yes | Yes | Lowers Box 1 and Boxes 3/5 |
| HSA via payroll (Section 125) | Yes | Yes | Lowers Box 1 and Boxes 3/5 |
| Traditional 401(k) / 403(b) / 457 | Yes | No | Lowers Box 1 only |
| Roth 401(k) | No | No | Nothing |
| Union dues, after-tax life, loan repayment | No | No | Nothing |
| Garnishment | No | No | Nothing |
The 2026 federal limits on the pre-tax side, for reference:
- 401(k), 403(b), 457 elective deferral: $24,500 (up from $23,500 in 2025)
- Catch-up, age 50+: $8,000
- Catch-up, age 60–63: $11,250
- Health FSA salary reduction: $3,400, with a carryover maximum of $680
- HSA: $4,400 individual, $8,750 family, plus $1,000 catch-up at 55+
- Social Security wage base: $184,500
One 2026 change is a pre-tax-versus-post-tax story on its own: catch-up contributions to an employer plan must now be made on a Roth (after-tax) basis if the employee earned more than $150,000 in the prior year. For those employees, a line that was pre-tax last year moves to the post-tax block this year, and the taxable wage base moves with it.
If you want to see what any of this does to a specific paycheck, the pre-tax vs post-tax deduction calculator runs both bases side by side. For the FICA half on its own, there’s a FICA tax calculator too.
Worked example: the same $200, three ways
Same employee, same pay period, same $200 deduction. The only variable is which bucket it lands in.
Setup: salaried employee, $78,000 a year, paid biweekly, so $3,000 gross per period. Single filer, standard deduction, no state income tax (to keep the arithmetic visible). Federal income tax is estimated by annualizing the period’s taxable wages against the 2026 brackets: $16,100 standard deduction, 10% to $12,400, 12% to $50,400, 22% above that.
Case A: the $200 is post-tax (Roth 401(k), union dues, a garnishment)
| Line | Amount |
|---|---|
| Gross | $3,000.00 |
| Pre-tax deductions | $0.00 |
| Taxable wages (income tax) | $3,000.00 |
| Taxable wages (FICA) | $3,000.00 |
| Federal income tax | $320.38 |
| Social Security (6.2%) | $186.00 |
| Medicare (1.45%) | $43.50 |
| Post-tax deduction | $200.00 |
| Net pay | $2,250.12 |
Case B: the $200 is a traditional 401(k) deferral
| Line | Amount |
|---|---|
| Gross | $3,000.00 |
| Pre-tax deduction (401k) | $200.00 |
| Taxable wages (income tax) | $2,800.00 |
| Taxable wages (FICA) | $3,000.00 |
| Federal income tax | $276.38 |
| Social Security (6.2% of $3,000) | $186.00 |
| Medicare (1.45% of $3,000) | $43.50 |
| Post-tax deductions | $0.00 |
| Net pay | $2,294.12 |
Two different taxable bases on one stub. The income tax line was computed on $2,800, the FICA lines on $3,000. That’s the rule working exactly as written.
Case C: the $200 is a Section 125 health premium
| Line | Amount |
|---|---|
| Gross | $3,000.00 |
| Pre-tax deduction (health premium) | $200.00 |
| Taxable wages (income tax) | $2,800.00 |
| Taxable wages (FICA) | $2,800.00 |
| Federal income tax | $276.38 |
| Social Security (6.2% of $2,800) | $173.60 |
| Medicare (1.45% of $2,800) | $40.60 |
| Post-tax deductions | $0.00 |
| Net pay | $2,309.42 |
What the three cases cost
| Net pay | Cost of the $200 | |
|---|---|---|
| Post-tax | $2,250.12 | $200.00 out of pocket |
| Traditional 401(k) | $2,294.12 | $156.00 out of pocket |
| Section 125 premium | $2,309.42 | $140.70 out of pocket |
The 401(k) dollar saved $44.00, which is 22% of $200: the marginal income tax rate, and nothing else. The Section 125 dollar saved $59.30, which is 22% plus the 7.65% employee FICA share. Same $200, same paycheck, $15.30 apart, and the only difference is which pre-tax category it belongs to.
Run your own numbers through the pre-tax vs post-tax deduction calculator if you want to see the split at your own pay rate. It also handles the awkward case where an employee crosses the $184,500 Social Security wage base partway through the year, at which point the Section 125 advantage shrinks to the Medicare portion.
Post-tax lines have rules too: garnishments and disposable earnings
Post-tax deductions get treated as an afterthought: whatever’s left, in whatever order. Union dues tolerate that. Garnishments have a federal ceiling that depends on getting the base right.
Federal wage garnishment limits under Title III of the Consumer Credit Protection Act are computed on disposable earnings, which the Department of Labor defines as pay remaining after deductions required by law. Taxes count. Voluntary deductions do not, no matter how pre-tax they are. Health premiums, 401(k) deferrals, and life insurance are all outside the definition. See DOL Fact Sheet #30.
For ordinary debts the weekly ceiling is the lesser of 25% of disposable earnings, or the amount by which disposable earnings exceed 30 times the federal minimum wage ($7.25 × 30 = $217.50 a week). Support orders, tax levies, and student loans follow separate rules, and several states cap garnishments more tightly than federal law does.
Take Case B above. Disposable earnings are $3,000 minus $505.88 of taxes, so $2,494.12 for the two-week period. Twenty-five percent is $623.53. The 30× floor for two weeks is $435, and disposable earnings exceed it by $2,059.12. The lesser figure wins, so the ceiling is $623.53.
The 401(k) deferral never removed $200 from the garnishable base. It pushed the other way. By lowering income tax withheld from $320.38 to $276.38, it raised disposable earnings by $44, and raised the garnishment ceiling by $11.00.
Deferring more into a pre-tax retirement plan slightly increases what a creditor can take. That surprises almost everyone, including some people who run payroll for a living, and it falls straight out of the definition.
Getting the categories right when you build the stub
If you produce stubs, the categorization decision is the whole game. Everything downstream (taxable wages, withholding, net pay, the W-2 boxes at year end) inherits it.
Three questions, in order, for each deduction line:
- Is it legally required? Taxes and court-ordered garnishments. Taxes go in the tax block; garnishments are post-tax but come out of disposable earnings.
- If it’s voluntary, is it pre-tax? Only if it runs through a qualifying arrangement: a Section 125 cafeteria plan, or a salary-reduction retirement deferral. A premium the employee pays personally, outside the employer’s plan, is post-tax.
- If it’s pre-tax, does it dodge FICA? Section 125 yes, traditional retirement no.
Get those three right and the stub reconciles. Get one wrong and it stays wrong every period until someone notices, usually in January.
This is one of the places where a purpose-built tool earns its keep over a spreadsheet template. Payslip44 makes the three-way choice explicit on every deduction line (Tax, Pre-tax, After-tax), renders the blocks in the order above, and computes gross, total deductions, and net in decimal arithmetic so the totals don’t drift by a cent. Reusable item templates mean you make the classification call once and replay it, and that’s what kills repeat errors: the health premium stays Section 125 pre-tax in period 14 because that’s how you set it up in period 1.
Each line also carries its own year-to-date column, so the running pre-tax totals are visible on the stub rather than reconstructed in April. Six layouts, and export to PDF, PNG, CSV, or text when you’re done.
One honest boundary: Payslip44 is a document builder, not a tax engine. It doesn’t derive withholding from IRS tables. You enter the tax figures, or produce them with the calculators, and the app makes sure the document that carries them is structured and totalled correctly. If you find a mis-categorized line on a stub you already issued, our guide on how to correct a pay stub covers the fix.
The short version
Pre-tax comes out before withholding is computed and lowers the wage base. Post-tax comes out after and lowers only net pay. On the stub the sequence runs gross, pre-tax, taxes, post-tax, net, and that sequence is what makes the numbers checkable.
Inside “pre-tax,” Section 125 items dodge income tax and FICA while traditional retirement deferrals dodge income tax only. On a $200 deduction that’s $15.30 a period, and at year end it’s the gap between Box 1 and Box 3.
And don’t assume post-tax means unregulated. Garnishments come out of disposable earnings, a base your voluntary benefits never touch.
Payslip44 builds stubs line by line with the deduction categories separated the way the math requires, decimal-precise totals, per-line YTD, and export to PDF, PNG, CSV, or text, all on-device. Download it and set the categories once.
Frequently Asked Questions
What is the difference between pre-tax and post-tax deductions?
Pre-tax deductions come out of gross pay before withholding is calculated, so they lower the wages your taxes are computed on. Post-tax deductions come out after the tax lines and only reduce your take-home pay.
Are 401(k) contributions pre-tax or post-tax?
Traditional 401(k) deferrals are pre-tax for federal income tax but still count as Social Security and Medicare wages. Roth 401(k) contributions are post-tax and reduce nothing on the tax side.
Is health insurance pre-tax or post-tax?
Employer-sponsored premiums run through a Section 125 cafeteria plan are pre-tax and escape both income tax and FICA. Coverage you buy yourself outside the employer's plan is post-tax.
Do pre-tax deductions reduce Social Security and Medicare taxes?
Section 125 items do. Traditional retirement deferrals do not, which is why W-2 Box 1 is often smaller than Boxes 3 and 5.
What order do deductions come out of a paycheck?
Gross pay, then pre-tax deductions, then tax withholding, then post-tax deductions, then net pay. The order is what makes the tax figures on the stub correct.
Which is better, pre-tax or post-tax?
Pre-tax gives a bigger paycheck now; post-tax (Roth) gives tax-free money later. It depends on your bracket today versus the one you expect in retirement, and many people split between the two.
Do pre-tax deductions reduce a wage garnishment?
No. Garnishments are calculated on disposable earnings, meaning pay after legally required deductions such as taxes, so voluntary pre-tax benefits do not shrink the garnishable amount.
Why doesn't my gross pay match the wages on my W-2?
Pre-tax deductions are subtracted before the W-2 wage boxes are filled in, so Box 1 is normally lower than your YTD gross. The gap is usually your pre-tax benefits and retirement deferrals.