Post-tax deductions are amounts your employer takes out of your paycheck after federal income tax, any state and local income taxes, and FICA taxes have already been withheld. Because the money has already been taxed, these deductions don’t lower your current taxable income the way a traditional 401(k) contribution or pre-tax health premium does. They still reduce your take-home pay dollar for dollar. Some are voluntary and buy you a future tax benefit; others are legally mandated and simply satisfy a debt.
Where Post-Tax Deductions Sit in Your Paycheck
Every paycheck runs through the same order of operations. Your employer starts with gross pay, subtracts pre-tax deductions (things like traditional 401(k) contributions or employer health insurance premiums), then calculates and withholds the mandatory taxes on what’s left. Only after all of that does the employer subtract post-tax deductions. What remains is your net pay.
The mandatory taxes withheld before any post-tax deduction include federal income tax, applicable state and local income taxes, and FICA. FICA is a 6.2% Social Security tax and a 1.45% Medicare tax on the employee side.1Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates Employees earning above $200,000 (single filers) also pay an additional 0.9% Medicare tax on wages above that threshold.2Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
That placement is the whole distinction. A $200 post-tax deduction reduces your net pay by $200 and does nothing to your taxable income. A $200 pre-tax deduction would have lowered your taxable wages first, meaning less income tax and, in most cases, less FICA that pay period. Same amount removed from your paycheck, very different tax outcome.
Common Examples of Post-Tax Deductions
A handful of items show up on most pay stubs as post-tax. Some you elect; some you can’t refuse.
Roth Retirement Contributions
The most common voluntary post-tax deduction is a contribution to a Roth 401(k), Roth 403(b), or governmental Roth 457(b) plan. You pay income tax on the money now, in the year you earn it. In exchange, both your contributions and their investment earnings come out completely tax-free in retirement, as long as the withdrawal qualifies.3Internal Revenue Service. Roth Account in Your Retirement Plan
A withdrawal qualifies as tax-free when two conditions are met: it’s been at least five years since your first Roth contribution to that plan, and you’re at least 59½ (or the withdrawal is due to disability or death).4Internal Revenue Service. Retirement Topics – Designated Roth Account Miss either condition and the earnings portion of the withdrawal can be taxed.
Certain Insurance Premiums
Some employer-sponsored insurance premiums are deducted post-tax on purpose, to protect the tax treatment of future benefits. Long-term disability insurance is the clearest case. If you pay premiums with after-tax dollars, any disability benefits you later receive are not taxable income.5Internal Revenue Service. Life Insurance and Disability Insurance Proceeds If your employer pays the premiums, or you pay them pre-tax through a cafeteria plan, disability benefits become taxable when you collect them.
Group-term life insurance gets a split treatment. The first $50,000 of employer-provided coverage is tax-free under IRC Section 79.6Office of the Law Revision Counsel. 26 U.S. Code 79 – Group-Term Life Insurance Purchased for Employees Coverage above $50,000 generates “imputed income”: the cost of that excess coverage is added to your taxable wages even though you never see the money.7Internal Revenue Service. Group-Term Life Insurance Supplemental life insurance you buy above the employer amount is typically deducted post-tax too.
Union Dues
Union dues are always deducted post-tax because they don’t qualify for any pre-tax exclusion from wages. Your full wages are taxed first, and the dues come out afterward.
Wage Garnishments
Not every post-tax deduction is voluntary. Employers are sometimes legally required to withhold money from your already-taxed wages, most commonly through a wage garnishment: a legal order directing your employer to send a portion of your pay to a creditor, government agency, or person you owe support to.8U.S. Department of Labor. Fact Sheet 30 – Wage Garnishment Protections of the Consumer Credit Protection Act You don’t get a say. Your employer must comply.
Federal law caps how much can be taken. For ordinary consumer debts like credit card judgments or medical debt, the Consumer Credit Protection Act limits garnishment to the lesser of 25% of your disposable earnings for the week, or the amount by which your weekly disposable earnings exceed 30 times the federal minimum wage.9Office of the Law Revision Counsel. 15 USC 1673 – Restriction on Garnishment Support orders follow a more aggressive schedule: up to 50% of disposable earnings if you’re supporting another spouse or child, up to 60% if you’re not, and an extra 5 points on either figure if you’re more than 12 weeks behind. Child support withholding also takes priority over most other garnishments, with the only exception being an IRS tax levy entered before the underlying support order.10Administration for Children and Families. Income Withholding Federal and state tax levies operate under their own formulas and are not bound by the 25% CCPA cap.
Pre-Tax vs. Post-Tax, in Plain Terms
The short version: pre-tax deductions save you money now and get taxed later, while post-tax deductions get taxed now and may save you money later. Most employees have a mix of both on every paycheck.
Common pre-tax items include traditional 401(k) contributions, employer-sponsored health insurance premiums, HSA contributions, and FSA contributions. These lower the wages reported in Box 1 of your W-2, which directly reduces your federal income tax for the year. Most also reduce Social Security and Medicare wages, saving FICA.
Post-tax deductions leave your reported wages alone. They come out of money you’ve already been taxed on. That looks worse in the moment, but some carry a real long-term advantage. Roth contributions grow and pay out tax-free in retirement. Paying disability premiums after tax means you won’t owe tax on the benefits if you ever need them. The timing of the tax hit is different, not necessarily the total cost.
How Post-Tax Deductions Show Up on Your W-2
Because post-tax deductions don’t reduce taxable wages, your W-2 Box 1 still reflects the full taxable amount before those deductions were taken. Boxes 3 and 5, which show Social Security and Medicare wages, are also unaffected. In effect, the deductions disappear from the wage figures on the form since the tax was already collected on that money.
Roth retirement contributions are the visible exception. Your employer reports them in Box 12 with specific letter codes: code AA for Roth 401(k), code BB for Roth 403(b), and code EE for governmental Roth 457(b).11Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 Those amounts are included in Box 1 (you already paid tax on them) but tracked separately so the IRS can monitor your contributions against the annual limit. If you contributed to both a traditional and a Roth side of the same plan, you’ll see two codes in Box 12.
Other post-tax items like union dues, supplemental insurance premiums, and garnishments don’t get their own Box 12 codes. Some employers report union dues in Box 14, which is a catch-all for additional information. Box 14 entries are informational and don’t feed directly into your return.
When Post-Tax Makes More Sense Than Pre-Tax
The post-tax route costs more in the current paycheck. That isn’t debatable. But there are situations where it clearly wins over the long term.
For retirement, if you’re relatively early in your career and your income is likely to rise, locking in today’s lower tax rate through Roth contributions means you avoid paying a higher rate on the same dollars decades from now. If you expect retirement tax rates to be higher than current rates, the same logic holds even if your personal income stays flat.
For insurance, the disability calculation is one of the easier calls in benefits enrollment. The small ongoing cost of paying premiums post-tax is trivial next to the tax bill you’d face on years of disability benefits if those premiums had been paid pre-tax. Owing income tax on replacement income during a period when you can’t work is exactly the wrong time for a tax bill.
Garnishments, of course, aren’t a choice. Understanding the caps still matters. Employers occasionally miscalculate, and knowing that consumer debt garnishments can’t exceed 25% of disposable earnings gives you a number to check against your pay stub.