Pay stub deductions explained: pre-tax vs post-tax
Pay stub deductions are amounts taken out of gross pay in addition to taxes. Pre-tax deductions, such as traditional 401(k) contributions and health premiums paid through a cafeteria plan, come out before income tax is figured. Post-tax deductions, such as Roth contributions, union dues and garnishments, come out afterward. Both reduce net pay; the difference is what they do to taxable wages.
Published . General information, not lending, legal or tax advice.
Where deductions sit on a stub
A stub separates what the employee earned, what the government takes (taxes), what the employee chose or was ordered to pay (deductions) and, on many stubs, what the employer contributes. Only the first three change net pay. The deduction lines hold most of the variety: retirement plans, insurance premiums, savings accounts, dues and court-ordered withholding.
Pre-tax versus post-tax is a taxable-wages distinction. A pre-tax deduction lowers the wages used to figure income tax, and sometimes payroll taxes, while a post-tax deduction does not. Either way the money leaves the paycheck, so in the gross vs net pay arithmetic they are all subtractions. For income calculations, monthly income from pay stubs starts from gross, before any of them.
How to read the deduction section
Take the lines one at a time, current column first.
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Find the section and what it contains
Separate taxes, deductions, employer contributions and reimbursements. Some stubs mix them in one block.
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Read the label and any pre-tax marker
Many stubs mark pre-tax lines with a heading, an asterisk or a code. Without a marker, treat the timing as unknown rather than guessing.
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Read current and year-to-date separately
The YTD column shows how long a deduction has been running and how much has been withheld in total.
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Add the lines and compare with the printed total
Check whether the printed total deductions includes taxes.
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Group the lines
Retirement, health and dental, garnishments and support, and everything else. A consistent grouping lets stubs be compared.
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Set employer contributions aside
An employer match and employer-paid premiums are information. They are not subtractions.
Common deductions and how they usually behave
Typical treatment. A plan or payroll setup can differ, so the stub and the plan documents settle any single line.
| Deduction | Usually | Lowers income-tax wages? | Note |
|---|---|---|---|
| Traditional 401(k), 403(b), 457(b) | Pre-tax | Yes | Typically still subject to Social Security and Medicare tax |
| Roth 401(k) | Post-tax | No | Often labelled Roth |
| Medical, dental and vision premiums | Pre-tax when paid through a cafeteria plan | Yes | Often exempt from Social Security and Medicare tax too |
| HSA or FSA through payroll | Pre-tax | Yes | Annual limits apply |
| Union dues | Post-tax | No | Flat amount or percent of pay |
| Garnishment, child support, tax levy | Post-tax | No | Ordered amounts; limits and priority set by law |
| 401(k) loan repayment | Post-tax | No | Repays the employee's own loan |
| Employer match or employer-paid premium | Not a deduction | Not applicable | Shown for information; does not reduce net pay |
What goes wrong
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Employer contributions subtracted
A match line near the deductions does not reduce net pay. Subtracting it makes net look too low.
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Total deductions that include taxes
Adding printed taxes on top of a total that already includes them counts them twice.
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Roth read as pre-tax
The two 401(k) lines look alike. Roth is after tax and does not lower taxable wages.
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A one-off deduction treated as recurring
A uniform charge, a repaid advance or a benefit true-up can appear on one stub. Check the YTD column and neighbouring stubs before treating it as ongoing.
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Mid-year changes
Benefit elections often change in January or after a life event. Net pay moves while gross does not.
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Garnishments over-read
A garnishment line shows an ordered withholding. What it means for a decision belongs to the program's rules, not to the person reading the stub. The checks that apply to every deduction are in pay stub arithmetic checks.
How VerifyStub helps
VerifyStub reads each deduction line, notes pre-tax or post-tax when the stub says which, and groups lines into retirement, health, dental, garnishment and other columns in the CSV, alongside pre-tax and post-tax totals. It tests that the lines add up to any printed total and that gross minus taxes and deductions equals net pay. It does not interpret what a deduction means for a decision. Try the pay stub to CSV page (free: 1 file per day, up to 10 pages, no account) or see pricing.
Scope. VerifyStub checks arithmetic on the pay stubs you upload. It does not detect altered documents, verify employment or income, or give lending, legal or tax advice. Rules and policies differ by lender, program, landlord and jurisdiction.
Pay stub deductions: common questions
What is the difference between pre-tax and post-tax deductions?
A pre-tax deduction is taken before income tax is figured, so it lowers taxable wages. A post-tax deduction is taken afterward and does not. Both reduce net pay.
Does a 401(k) contribution reduce gross pay?
No. Gross is shown before it. The contribution is a deduction that reduces net pay, and a traditional contribution also lowers the wages used for income tax. The stub's gross stays the same.
Why is gross on the stub higher than Box 1 on the W-2?
Box 1 is taxable wages after pre-tax items such as traditional 401(k) deferrals and cafeteria-plan benefits. The stub's gross is before them. Pay dated in another year can also create differences.
Are health insurance premiums always pre-tax?
Not always. Premiums paid through an employer's cafeteria plan are usually pre-tax, and other arrangements are after tax. The stub may mark which, and the plan documents settle it.
What does a garnishment on a stub mean?
It is a withholding ordered by a court or agency, for example for child support or a defaulted debt, and it is deducted after taxes. How a program treats it is set by that program.
Is the employer match a deduction?
No. An employer match is a contribution the employer makes. Stubs often list it for information, and it does not come out of the employee's pay.
Why did my deductions change mid-year?
Benefit elections can change at open enrollment, after a life event or when a plan year starts, and percent-based deductions move with pay. Compare the year-to-date column to see when the amount changed.
Keep reading
Related guides, or all of the pay stub guides.
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Gross vs net pay
Gross to net, line by line, with a worked stub and the lines most often misread.
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Pay stub arithmetic checks
The checks a reviewer runs on a stub, the allowance for each, and what a pass does and does not mean.
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Monthly income from pay stubs
The formula for weekly, biweekly, semimonthly and monthly stubs, with a worked table and the shortcuts that understate income.
Run the next stack of stubs through the checks
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