Self-Employment Tax Calculator — Methodology

Step-by-step calculation

Estimate the total tax bill for a freelancer or sole proprietor including SE tax, federal, and state.

1. 1

   Enter your net SE income

   Schedule C net profit — gross business revenue minus deductible business expenses.

2. 2

   Add other income

   W-2 wages, spouse income, investments — affects the federal bracket calculation.

3. 3

   Pick filing status and state tier

   Standard deduction and brackets differ by status. State tier is a simplification of the 50-state matrix.

4. 4

   Read the total tax and quarterly figure

   The quarterly amount is what to send to the IRS each quarter to avoid underpayment penalty.

Assumptions and overrides

2026 IRS brackets and SS wage base used (post-TCJA-indexed estimates — confirm against Rev. Proc. annual update). QBI deduction (Section 199A) not modelled; additional Medicare tax (0.9% above $200k single / $250k MFJ) not modelled. State tier is a simplified 3-band approximation, not state-bracket-accurate.

Every region default on the calculator is editable. If your effective rate, fee, or threshold differs from the headline figure shown, type your own number into the field — the calculator recomputes instantly without leaving this page.

Primary sources

Region-tagged primary sources for the default rates, thresholds, and benchmarks used in this calculator.

• USAIRS — Self-Employment Tax (US 15.3%)
• UKGOV.UK — Self-Assessment & Class 2/4 NI (UK)
• SASARS — Provisional Tax (SA)

Review cadence and corrections

This methodology and the underlying rate defaults are reviewed at least annually, and immediately following any change to the headline rate from IRS, HMRC, or SARS. Every substantive update is recorded on the public changelog. Spotted an error? See the corrections policy for how to report it.

See the full editorial policy for the standards every page on BusCalcTools is held to.