Sources
- IRS Schedule SE + Pub 334 - SE tax calculation methodology and the 92.35% net-earnings adjustment.
- IRS Rev. Proc. 2025-28 - 2026 federal income tax brackets, standard deductions, and QBI thresholds.
- SSA COLA announcement - 2026 Social Security wage base ($184,500).
- State revenue department rate tables - flat top-marginal state income tax rates for all 50 states + DC.
Calculation steps
- Net SE income = gross 1099 income minus business expenses, mileage deduction, health insurance, and retirement contributions.
- Taxable SE earnings = net SE income × 0.9235.
- SE tax = Social Security portion + Medicare portion + Additional Medicare tax (see SE Tax Calculator methodology for detail).
- AGI adjustment = net SE income − (SE tax × 50%) − QBI deduction + W-2 income.
- Taxable income = AGI adjustment − standard deduction.
- Federal income tax = progressive bracket calculation using 2026 IRS brackets (Single/MFJ; HoH and MFS use Single brackets in v1).
- State income tax = (AGI adjustment) × flat state top-marginal rate.
- Total tax = SE tax + federal income tax + state income tax.
2026 key constants
| Constant | Value |
|---|---|
| SS wage base | $184,500 |
| SS rate (self-employed) | 12.4% |
| Medicare rate | 2.9% |
| Additional Medicare | 0.9% above threshold |
| Net earnings adjustment | 92.35% |
| Standard deduction (single) | $16,100 |
| Standard deduction (MFJ) | $32,200 |
| QBI deduction rate | 20% |
Limitations
- State tax uses a flat top-marginal rate - overestimates state tax for moderate incomes in states with progressive brackets.
- HoH and MFS filers use Single federal brackets (v1 approximation).
- QBI phase-outs for high incomes and specified service businesses are not modelled.
- AMT, tax credits, and multi-state income are not supported.
Results are estimates for planning purposes only. Consult a licensed CPA or Enrolled Agent for your actual tax liability.