A post-tax deduction is any amount your employer subtracts from your paycheck after federal income tax, Social Security, and Medicare have already been withheld. Because the taxes are calculated first, these deductions do not lower your taxable income for that pay period. Roth 401(k) contributions are the most common voluntary example; wage garnishments, certain insurance premiums, union dues, and payroll charitable gifts also fall into this category.
Where Post-Tax Deductions Sit in the Payroll Sequence
Every paycheck follows the same order. Your employer starts with gross pay, subtracts pre-tax items like traditional 401(k) contributions or health insurance premiums, and arrives at your taxable income for the period. Federal income tax, Social Security at 6.2%, and Medicare at 1.45% are all calculated on that reduced figure and withheld. Only after those taxes come out does the employer subtract anything labeled post-tax.
That ordering is the entire distinction. A $200 pre-tax deduction shrinks the income your taxes are based on, so your tax bill goes down. A $200 post-tax deduction comes out after the tax math is finished, so your tax bill is unchanged and your take-home pay drops by the full $200. The money still goes somewhere useful, whether a Roth account or a court-ordered debt, but it buys you no break on this paycheck.
What Counts as a Post-Tax Deduction
Roth 401(k) and Roth IRA Contributions
Roth retirement contributions are the post-tax deduction most workers choose on purpose. You pay income tax on the money now, and qualified withdrawals in retirement come out completely tax-free, including every dollar of investment growth, as long as the account has been open at least five years and you are 59½ or older.1Internal Revenue Service. Roth Comparison Chart That is the mirror image of a traditional 401(k), where the contribution lowers today’s taxes but every withdrawal in retirement is taxed as ordinary income.
For 2026, you can defer up to $24,500 into a Roth 401(k). Workers 50 or older can add $8,000 in catch-up contributions, and a newer provision for ages 60 through 63 allows a higher catch-up of $11,250 if the plan permits it. Those limits apply to the combined total of your traditional and Roth 401(k) contributions, not each type separately. Roth IRA contributions are also post-tax, with a 2026 limit of $7,500, though the ability to contribute phases out at higher incomes.2Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
Wage Garnishments
A wage garnishment is a legally required deduction, usually ordered by a court, that directs your employer to withhold part of your pay to satisfy a debt.3U.S. Department of Labor. Wage and Hour Division Fact Sheet 30 – Wage Garnishment Protections of the Consumer Credit Protection Act You do not choose this one. Common triggers are unpaid consumer debts, child support, back taxes, and defaulted student loans.
Federal law caps garnishment for ordinary consumer debts at the lesser of 25% of your disposable earnings for the week or the amount by which weekly disposable earnings exceed 30 times the federal minimum wage. Support orders can reach 50% or 60% of disposable earnings, depending on whether you are supporting another spouse or child, with an added 5% if the support is more than 12 weeks overdue.4Office of the Law Revision Counsel. 15 USC 1673 – Restriction on Garnishment
Insurance Premiums, Union Dues, and Charitable Gifts
Several other paycheck subtractions typically come out after taxes:
- Supplemental life insurance. Employer-provided group-term life insurance is tax-free up to $50,000 of coverage. Premiums you pay for coverage above that threshold are usually deducted post-tax.5Internal Revenue Service. Group-Term Life Insurance
- Employee-paid disability insurance. When premiums are paid with post-tax dollars, any benefits you later receive if you become disabled are generally tax-free. If your employer offers a choice, that trade-off is worth weighing against the smaller pre-tax paycheck hit.
- Union dues. These are usually processed post-tax, though the exact handling depends on the collective bargaining agreement and your employer’s payroll setup.
- Charitable contributions. Some employers let you donate to charities directly from your paycheck. These come out post-tax but may still be deductible on your annual return.
Post-Tax Does Not Always Mean No Tax Benefit
This is where people get tripped up. A deduction that fails to reduce your payroll taxes is not necessarily invisible to the IRS at year-end.
Charitable contributions made through payroll are the clearest example. They are withheld after taxes on each paycheck, but you can claim them as an itemized deduction on Schedule A just like any other charitable gift. The IRS treats each payroll deduction as a separate contribution, so hang on to your pay stubs or W-2 as documentation.6Internal Revenue Service. Instructions for Schedule A (Form 1040) For gifts of $250 or more per paycheck, you will also need a written acknowledgment from the charity.7Internal Revenue Service. Charitable Contributions – Substantiation and Disclosure Requirements (Publication 1771)
Union dues may also be deductible on your 2026 return. The Tax Cuts and Jobs Act suspended the miscellaneous itemized deduction that covered union dues starting in 2018, and that suspension was scheduled to expire at the end of 2025. If Congress did not extend it, union dues become deductible again as a miscellaneous itemized deduction subject to a 2% floor of adjusted gross income. Check current IRS guidance when filing.
Other post-tax deductions give you nothing back. A garnishment is money taken out of fully taxed wages to pay a debt; there is no deduction waiting on the other end. The label “post-tax” tells you when the deduction happens in your payroll cycle, not whether it can ever lower your taxes.
How Post-Tax Deductions Show Up on Your W-2
Post-tax deductions do not reduce the taxable wages reported on your W-2. Roth 401(k) contributions, for example, are included in Box 1 (wages, tips, other compensation) and in Boxes 3 and 5 (Social Security and Medicare wages).8Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 That is consistent with the mechanics: you already paid tax on that money, so it belongs in the taxable wage figures.
To separately identify your Roth 401(k) contributions, look at Box 12. Your employer reports the total using code AA.8Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 That coding tells the IRS you have already paid tax on those dollars, which matters decades later when you take qualified withdrawals.
Other post-tax items like union dues, disability premiums, or charitable contributions sometimes appear in Box 14, which employers use for miscellaneous information. Box 14 labels are not standardized across employers, so if something there looks unfamiliar, ask your payroll department what it represents before you file.
Compare that to a pre-tax traditional 401(k) contribution, which reduces your Box 1 wages. If you earned $70,000 and contributed $5,000 pre-tax, Box 1 shows $65,000. Contribute the same $5,000 to a Roth 401(k) instead and Box 1 shows the full $70,000.9Internal Revenue Service. Retirement Plan FAQs Regarding Contributions That is the pre-tax versus post-tax distinction playing out in real numbers.
Pre-Tax vs. Post-Tax at a Glance
The choice, where you have one, comes down to when you want your tax break. Pre-tax deductions save you money right now by lowering this year’s taxable income. Post-tax Roth deductions save you nothing today but let you withdraw everything tax-free later.10Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts Neither is universally better; it depends on where you expect your tax rate to land when you use the money.
A traditional 401(k) contribution of $10,000 in the 24% bracket saves roughly $2,400 in federal income tax this year, but every dollar pulled out in retirement is taxed at your bracket then. A Roth 401(k) contribution flips the math: you pay the full tax now, and retirement withdrawals (including decades of growth) come out federal-income-tax-free. Many financial planners suggest splitting contributions between both types if you are unsure.
And some post-tax deductions involve no choice at all. Garnishments and court-ordered support payments come out after taxes because the law requires it. Supplemental insurance premiums land there because of how the employer-provided benefit is structured. In both cases, “post-tax” is simply where the deduction sits in the payroll sequence, not a tax strategy you selected.