Every line on your paycheck falls into one of two buckets. Mandatory payroll deductions are the withholdings your employer must take because federal, state, or local law requires them, and voluntary payroll deductions are the ones that only appear because you signed something authorizing them. That’s the whole distinction. Knowing which is which tells you where you have room to shape your take-home pay and where you don’t.
What Counts as Mandatory
Your employer has no discretion over mandatory deductions, and neither do you.1eCFR. 29 CFR 3.5 – Payroll Deductions Permissible Without Application to or Approval of the Secretary of Labor The standard list:
- Federal income tax, calculated from the information you provide on Form W-4, including your filing status, dependents, and any additional withholding you request.2Internal Revenue Service. About Form W-4, Employee’s Withholding Certificate
- Social Security tax at 6.2% of wages, up to a taxable earnings cap of $184,500 in 2026.3Social Security Administration. What is FICA?4Social Security Administration. Contribution and Benefit Base
- Medicare tax at 1.45% of all wages with no cap, plus an extra 0.9% on wages above $200,000 in a calendar year.5Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
- State and local income taxes, required in most states and some cities or counties, with rates and rules varying by jurisdiction.
- Court-ordered garnishments for child support, unpaid taxes, or creditor judgments. When an order comes in, your employer must comply, and you can’t stop the deduction by asking HR.
W-4 adjustments are the one lever you have on this side of the pay stub. Everything else here is fixed by the rate schedule or the order itself.
What Counts as Voluntary
Anything on your pay stub that isn’t required by statute or a court order is voluntary. It only appears because you elected it, and it typically comes off only after you sign a written authorization specifying the amount, effective date, and destination.
Retirement Contributions
Most workplace retirement savings come through payroll. In a 401(k), 403(b), or governmental 457 plan, you defer part of your salary into an individual account.6Internal Revenue Service. 401(k) Plans For 2026, elective deferrals are capped at $24,500, with an $8,000 catch-up if you’re 50 or older and an $11,250 catch-up for workers aged 60 through 63 under SECURE 2.0.7Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Smaller employers often use a SIMPLE IRA instead, where the 2026 deferral limit is $17,000 with lower catch-up amounts.8Internal Revenue Service. SIMPLE IRA Contribution Limits You choose the contribution rate, and you can usually change it.
Health Insurance Premiums
If your employer offers group health coverage, your share of the premium is voluntary. Nobody forces you to enroll. Most employers run health, dental, and vision premiums through a Section 125 cafeteria plan, which pulls the premium out before federal income tax and before Social Security and Medicare are calculated.9Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans The trade-off is limited flexibility: once you enroll, you generally can’t change the election until the next open enrollment or a qualifying life event like marriage, a birth, or loss of other coverage. Supplemental coverages like group life, long-term disability, and accident insurance follow the same voluntary pattern.
HSAs and FSAs
A health savings account, funded through payroll if you’re enrolled in a high-deductible health plan, has a 2026 contribution limit of $4,400 for self-only coverage and $8,750 for family coverage.10Internal Revenue Service. Revenue Procedure 2025-19 Routed through a cafeteria plan, HSA contributions dodge income tax and FICA. Balances roll over indefinitely.
A health care FSA is different. You elect a fixed amount at enrollment, capped at $3,400 for 2026, and up to $680 in unused funds can carry over into the following year if your plan allows it. Changing your FSA election mid-year requires a qualifying life event.
Everything Else
Several other deductions require your authorization:
- Employee stock purchase plan contributions, often used to buy company stock at up to a 15% discount.
- Union dues, which members authorize in writing before the employer withholds and forwards them.11U.S. Federal Labor Relations Authority. 5 USC 7115 – Allotments to Representatives
- Charitable contributions directed through payroll to a chosen organization or workplace campaign.
- Repayments of an employer loan or pay advance, on terms spelled out in the loan agreement.
- Commuter benefits, employer-sponsored parking, and gym memberships.
The common thread is consent. None of these can show up on your pay stub without it.
Pre-Tax vs. Post-Tax
Not every voluntary deduction saves you the same amount in taxes, and the difference matters.
Health insurance premiums and HSA contributions run through a Section 125 cafeteria plan are exempt from federal income tax, Social Security tax, and Medicare tax.9Internal Revenue Service. FAQs for Government Entities Regarding Cafeteria Plans That’s the full sweep of payroll taxes.
Traditional 401(k) contributions get a narrower break. They’re exempt from federal income tax, but Social Security and Medicare taxes are still withheld on the amount you defer.12Internal Revenue Service. Are Retirement Plan Contributions Subject to Withholding for FICA, Medicare, or Federal Income Tax If you defer $1,000, your income tax withholding drops, but the 6.2% Social Security tax and 1.45% Medicare tax still come out of that $1,000.
Roth 401(k) contributions are post-tax. Income tax, Social Security, and Medicare are calculated on the full gross, and the contribution comes out of what’s left; qualified withdrawals in retirement are then tax-free.6Internal Revenue Service. 401(k) Plans Union dues, charitable contributions, and ESPP deductions are also post-tax.
Authorization, Changes, and the Wage Floor
Your written authorization is what makes a voluntary deduction legal. Without one on file, an employer who withholds money for a voluntary purpose has effectively made an unauthorized wage deduction, which can expose them to a wage claim. The authorization typically takes the form of a signed consent or benefit enrollment form specifying the exact dollar amount or percentage, the effective date, and where the money goes.
You can usually stop or adjust a voluntary deduction, but flexibility varies. Many retirement plans let you change your deferral rate at any time, or at least once per quarter. Section 125 elections are more rigid because the tax break is tied to restricted election windows. A loan repayment deduction may be locked in by the terms of your loan agreement. To change or cancel, start with HR, get confirmation in writing, and check your next pay stub.
One safeguard rarely surfaces until something goes wrong: voluntary deductions generally cannot push your effective pay below the federal minimum wage. The Fair Labor Standards Act requires that wages be paid free and clear, meaning deductions can’t be used to claw back wages in a way that benefits the employer or drops your pay below the minimum.13eCFR. 29 CFR 531.35 – Wage Payments Free and Clear Federal rules also bar employers from profiting, directly or indirectly, from voluntary deductions sent to third parties like insurers or charities.14eCFR. 29 CFR 531.40 – Payments to Employee’s Assignee Some states apply their own minimum wage as the floor, which may be higher. If you earn close to minimum wage and have several voluntary deductions stacking up, check the math on your pay stub.