Self employment tax calculator for online sellers, at 2026 rates.

How it's worked out

The self-employment tax formula for 2026.

Self-employment tax is Social Security and Medicare tax for people who work for themselves. The IRS sets the rate at 15.3%: 12.4% for Social Security and 2.9% for Medicare. You owe it, and file Schedule SE, when your net earnings from self-employment are $400 or more.

Net earnings = net profit × 92.35%
Under 400.00 of net earnings: no self-employment tax

Social Security part = 12.4% × the smaller of net earnings or (184,500.00 − W-2 Social Security wages)
Medicare part = 2.9% × net earnings

Self-employment tax = Social Security part + Medicare part
Deduction = 50% × self-employment tax

The 184,500.00 is the 2026 Social Security wage base: the most earnings, wages and self-employment combined, that carry Social Security tax in the year. Wages from a job count first, so a seller with a salary pays the 12.4% only on the room left above them. The 2.9% Medicare part has no cap.

The deduction for half of self-employment tax comes off when you work out adjusted gross income. The IRS notes it lowers income tax only; it does not change net earnings or the self-employment tax itself.

Additional Medicare Tax = 0.9% × (net earnings − (threshold − W-2 Medicare wages))

The Additional Medicare Tax is a separate 0.9% on Medicare wages and self-employment income over a threshold for your filing status: 250,000.00 married filing jointly, 125,000.00 married filing separately and 200,000.00 for everyone else. It is reported on Form 8959, and it is not part of the self-employment tax or the half deduction.

The sample: 85,000.00 × 92.35% = 78,497.50 of net earnings. 12.4% of that is 9,733.69 and 2.9% is 2,276.43, so self-employment tax is 12,010.12 and the deduction is 6,005.06. Each line is rounded to the cent. To turn this into quarterly payments, with income tax added, use the quarterly tax calculator.

This is an estimate for planning, built for a sole proprietor or single-owner business filing Schedule C. It covers the regular method on Schedule SE; farm income, church employee income and the optional methods have their own rules on the form. Your tax preparer confirms the amounts for your return.

Sources

1. IRS: Self-employment tax (Social Security and Medicare taxes), fetched 7 Oct 2026 — 15.3% rate, 12.4% and 2.9% parts, $400 filing floor, deduction for the employer-equivalent portion.
2. IRS: Schedule SE (Form 1040), 2025, fetched 7 Oct 2026 — 92.35% factor (line 4a), the $400 stop (line 4c), 12.4% and 2.9% (lines 10–11), 50% deduction (line 13).
3. IRS: Form 1040-ES (2026), Self-Employment Tax and Deduction Worksheet, fetched 7 Oct 2026 — the same steps for 2026, with the $184,500 Social Security maximum on line 5.
4. Social Security Administration: Contribution and benefit base, fetched 7 Oct 2026 — 2026 base of $184,500 and the 12.4% self-employment rate.
5. IRS: Questions and answers for the Additional Medicare Tax, fetched 7 Oct 2026 — 0.9% rate and thresholds by filing status.
6. IRS: Form 8959, Additional Medicare Tax, fetched 7 Oct 2026 — Part II: threshold less Medicare wages, applied to self-employment income.