Separate withholding from benefit deductions
Federal income tax, state or local income tax, Social Security, and Medicare are tax deductions from ordinary employee wages. Health premiums, retirement contributions, union dues, garnishments, and other elections are different kinds of payroll deductions. Label them separately when checking a stub so an increased retirement contribution is not mistaken for an increased tax rate.
Some amounts on a stub are employer expenses or informational benefit totals, not employee deductions. An employer’s retirement match, employer Social Security share, or employer-paid premium should not be entered as a cash deduction from your paycheck. Start with the employee columns and confirm unfamiliar abbreviations with payroll.
Traditional and Roth retirement contributions are different
Qualifying traditional 401(k) salary deferrals are generally excluded from federal income-tax wages but still subject to Social Security and Medicare. They lower the amount available for current spending even though they are being saved for retirement. Designated Roth contributions are generally included in current federal taxable wages and are deducted from after-tax pay.
Our traditional 401(k) input models that federal income-tax reduction while retaining FICA taxation. A Roth contribution belongs in post-tax deductions. State tax treatment is not universally the same: Pennsylvania generally includes employee retirement deferrals in taxable compensation, while New Jersey excludes qualifying 401(k) deferrals but can tax other plan types. Use a known state wage base rather than assuming a federal exclusion applies everywhere.
Sources: IRS — retirement plan FAQs regarding contributions; Pennsylvania personal income-tax guide — compensation; New Jersey GIT-1 — retirement plan tax treatment
Health coverage depends on how the plan is arranged
Employee health premiums paid under a qualifying Section 125 cafeteria plan are generally excluded from federal income-tax and FICA wages. Premiums paid after tax do not get that same payroll treatment. Other benefits, including flexible spending arrangements and health savings account contributions, have their own eligibility and contribution rules. A payroll label alone is not enough to establish the exclusion.
The health-insurance field assumes a qualifying pre-tax cafeteria plan. Our “other pre-tax” field lowers income-tax wages but does not lower FICA wages. Do not force a FICA-exempt benefit into that field and expect an exact payroll match. The site is not a complete benefits-tax engine: use actual payroll treatment and the methodology to decide whether the model fits your check.
Local taxes and payroll programs need their own lines
A state income-tax deduction may sit alongside county or city withholding, disability insurance, paid family leave, or a long-term-care contribution. These are not all state income tax. Some states with no individual wage income tax still have employee payroll programs.
In withholding mode, local tax and other payroll charges are entered as actual per-check dollar amounts. They are not independently calculated from your location. If you omit a real payroll premium, your estimated deposit can be too high. Enter the employee amount, not an employer contribution, and avoid duplicating a charge already included in post-tax deductions.
Garnishments and similar mandatory deductions also have legal limits and priority rules. Our post-tax field can subtract a known amount, but the calculator does not determine what an employer may legally withhold. For an unexplained charge, ask for the deduction’s authorization and calculation.
Map the stub before entering amounts
Use a single pay period for all ordinary deduction inputs. A monthly benefit cost must be allocated to the actual payroll schedule before being entered on a biweekly calculation; simply dividing by two can be wrong. Annual W-4 deduction elections are different from per-check benefit costs and have separately labeled inputs.
After mapping the lines, verify that gross pay minus employee taxes minus employee deductions equals the total net cash pay. If a pre-tax deduction exceeds the current gross pay, this site reports an input error rather than producing a misleading negative taxable wage. For irregular benefits, noncash compensation, or reimbursements, payroll records are the authoritative paycheck source.
Sources: IRS Form W-4 (2026) and instructions; IRS Publication 15-T (2026) — federal withholding methods
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