Sources
- IRS Schedule SE - the official form and instructions for computing self-employment tax (Part I, short schedule; Part II, long schedule for higher earners).
- IRS Publication 334 - Tax Guide for Small Business, covering Schedule C and the 92.35% net-earnings adjustment.
- IRS Publication 505 - Tax Withholding and Estimated Tax, covering quarterly payment rules and safe-harbor thresholds.
- SSA COLA announcement - Social Security wage base ($184,500 for TY 2026).
Calculation steps
- Net SE income = gross self-employment income minus deductible business expenses.
- Taxable SE earnings = net SE income × 0.9235 (the 92.35% adjustment that simulates the employer-half deduction).
- Social Security tax = min(taxable SE earnings, $184,500) × 12.4%.
- Medicare tax = taxable SE earnings × 2.9%.
- Additional Medicare tax = amount above the filing-status threshold × 0.9% (thresholds: $200,000 single/HoH, $250,000 MFJ, $125,000 MFS).
- Total SE tax = SS tax + Medicare tax + Additional Medicare tax.
Limitations
- Income tax is not calculated here - use the 1099 Tax Calculator for a full federal + state + SE estimate.
- The calculator does not account for W-2 Social Security wages already subject to FICA withholding, which can reduce the SE SS cap.
- QBI phase-outs, AMT, and tax credits are not modelled.
Results are estimates for planning purposes only. Consult a licensed CPA or Enrolled Agent for your actual tax liability.