1. Mathematical Foundations
Our calculation engine applies the official IRS Percentage Method for automated payroll systems as specified in 2026 IRS Publication 15-T (Federal Income Tax Withholding Methods).
2. 2026 Federal Income Tax Parameters
| Parameter | Single | Married Filing Jointly | Head of Household |
|---|---|---|---|
| Standard Deduction | $16,100 | $32,200 | $24,150 |
| Social Security Wage Base | $184,500 (6.2% withholding) | ||
| Medicare Tax Rate | 1.45% on all earnings | ||
| Additional Medicare (0.9%) | Over $200,000 | Over $250,000 | Over $200,000 |
3. State Income Tax Modeling
We maintain customized models for all 50 states and Washington D.C., categorized into:
- Zero-Tax States (9): AK, FL, NV, NH, SD, TN, TX, WA, WY. State tax = $0.
- Flat-Tax States (15): AZ (2.5%), CO (4.4%), GA (5.19%), ID (5.3%), IL (4.95%), IN (2.95%), IA (3.8%), KY (3.5%), LA (3.0%), MI (4.25%), MS (4.0%), NC (3.99%), OH (2.75%), PA (3.07%), UT (4.5%).
- Graduated Progressive States (27): Progressive tax brackets applied to state taxable income.
4. Annual Update Cadence
Tax rules are audited every October and finalized each January following the IRS cost-of-living inflation adjustments.