Federal income tax withholding
IRS Publication 15-T (2026)
Federal Income Tax Withholding Methods, including 2026 percentage method tables for automated payroll systems.
For a plain-language map of the employee form to NetPayKit inputs, read the 2026 Form W-4 guide.
These percentage-method rules also power the regular-pay search in the 2026 gross-up calculator.
2026 Form W-4
The employee form supplies filing status, Step 2(c), credits, other income, deductions, extra withholding, and any valid exempt claim used by the regular-pay calculators.
Bonus and supplemental wage withholding
IRS Publication 15 (2026), section 7
Section 7 defines supplemental wages and documents the optional 22% method, the aggregate method, the regular-wage withholding eligibility rule—which looks to regular-wage federal income tax withholding by the employer paying the bonus in the current or immediately preceding calendar year—and mandatory 37% withholding on calendar-year supplemental wages above $1 million.
Publication 15 states that the excess over $1 million is subject to mandatory 37% withholding. Treasury Decision 9276 also documents an employer election to apply 37% to the entire current supplemental payment that crosses the threshold. NetPayKit models the excess-only approach. Prior supplemental wages must include payments from businesses under common control.
Treasury Decision 9276 and Revenue Ruling 2008-29
Treasury Decision 9276 documents the alternative entire-payment election for a threshold-crossing payment. Revenue Ruling 2008-29 provides supplemental-wage withholding examples and payment-order guidance.
Read Treasury Decision 9276 · Read Revenue Ruling 2008-29
Read IRS Publication 15, section 7
Publication 15-T supplies the 2026 percentage method used for the aggregate calculation. See the 2026 bonus tax calculator.
Social Security and Medicare
IRS Publication 15 (2026)
Employer guidance for federal payroll tax, including 2026 employee and employer FICA rates, the Social Security wage base, and Additional Medicare withholding.
Social Security Administration wage base
The SSA contribution and benefit base determination documents the $184,500 Social Security wage base for 2026.
View the SSA wage-base determination
See the rates, annual limit, worked examples, and Additional Medicare distinction in the 2026 FICA rates and wage-base guide.
The gross-up calculator uses these employee FICA rules and the entered prior wages when solving for regular gross pay.
Overtime and the regular rate
U.S. Department of Labor Fact Sheet #23 (revised October 2019)
Federal guidance on the general overtime requirement for covered, nonexempt employees, the fixed 168-hour workweek, the prohibition on averaging hours across workweeks, and common regular-rate examples.
U.S. Department of Labor Fact Sheet #56A (December 2019)
Federal guidance on the regular rate of pay under the Fair Labor Standards Act and the general time-and-a-half requirement for covered nonexempt employees.
29 CFR Part 778 (eCFR current through August 17, 2026)
The current federal regulations explain overtime compensation and the regular rate under the Fair Labor Standards Act, including included compensation, statutory exclusions, and special methods.
Read 29 CFR Part 778 in the eCFR
Overtime sources and the current eCFR text were reviewed August 19, 2026. The overtime calculator is intentionally limited to one straightforward hourly scenario and does not determine coverage or exemption status.
How we use sources
Primary sources establish calculator constants and calculation concepts. NetPayKit summarizes them for a general audience but does not reproduce all agency instructions or cover every exception. Agency guidance controls if a summary conflicts with an official source.