Self-Employment Tax: Definition and How It Works

Self-employment tax (SE tax) is the Social Security and Medicare tax that self-employed individuals pay on net earnings from self-employment under the Self-Employment Contributions Act (SECA), codified at IRC §§1401–1403. While employees pay half of their FICA obligations (7.65%) and employers match the other half, self-employed individuals — sole proprietors, single-member LLC owners, partners in partnerships, and certain independent contractors — are both the employer and the employee, and pay the full combined rate. Understanding the SE tax calculation, the available above-the-line deduction, and the structural planning techniques that reduce exposure is among the most common areas of CPA advisory work for business-owner clients.

SE Tax Rates and the Wage Base

Self-employment tax is assessed at two rates under IRC §1401:

12.4% for Social Security (OASDI) on net SE earnings up to the annual Social Security wage base — $176,100 for 2026 (IRS Rev. Proc. 2025-XX; the base is indexed annually)
2.9% for Medicare (HI) on all net SE earnings with no cap

For high-income taxpayers, the Additional Medicare Tax (Net Investment Income Tax companion) adds 0.9% under IRC §3101(b)(2) on wages and SE earnings above $200,000 for single filers or $250,000 for married filing jointly. This brings the effective Medicare rate to 3.8% on SE earnings above those thresholds.

The combined SE tax rate on income below the Social Security wage base is 15.3%. Above the Social Security base, only the 2.9% (or 3.8%) Medicare component applies.

Calculating Net Earnings From Self-Employment

The SE tax is calculated on net earnings from self-employment — generally, gross income from a trade or business minus ordinary and necessary business expenses reported on Schedule C (for sole proprietors), or the distributive share of partnership/LLC income. Net earnings are then multiplied by 92.35% before applying the SE tax rate. The 92.35% factor exists because the Social Security and Medicare system allows self-employed individuals to deduct the "employer equivalent" half of their SE tax when computing the income subject to SE tax — an internal symmetry that roughly mirrors the pre-tax wage calculation for W-2 employees.

The formula: Net SE Income × 92.35% × 15.3% (up to Social Security base) + Net SE Income × 92.35% × 2.9% (above Social Security base).

The Above-the-Line Deduction for Half of SE Tax

IRC §164(f) allows self-employed individuals to deduct half of their SE tax as an above-the-line deduction from gross income (Form 1040, Schedule 1). This mirrors the employer's ability to deduct its share of FICA taxes as a business expense. The deduction reduces adjusted gross income (AGI) and thus reduces the income subject to federal income tax — but not the SE tax itself.

For a sole proprietor with $200,000 in net SE income, SE tax is approximately $29,500 (2026 figures). The deductible half is approximately $14,750, reducing AGI by that amount. At a marginal rate of 32%, this saves roughly $4,720 in income tax, partially offsetting the SE tax burden.

How the S-Corporation Election Reduces Self-Employment Tax

The most common SE tax reduction strategy is the S-Corporation election. An S-Corp shareholder-employee pays FICA (Social Security and Medicare) tax only on their W-2 salary — distributions from the S-Corp above the salary are not subject to FICA. Since SE tax is the self-employed equivalent of FICA, structuring income through an S-Corp effectively removes distributions from the SE tax base.

For a business generating $180,000 in net income where the shareholder takes a $90,000 reasonable salary and $90,000 in distributions: FICA tax applies only to the $90,000 W-2 salary, saving approximately $6,900–$7,200 in FICA/SE tax compared to a sole proprietor structure reporting all $180,000 as SE income. The savings grow with income (up to the Social Security wage base) and must be weighed against S-Corp compliance costs.

The IRS requires the salary to be "reasonable" — commensurate with the shareholder's services to the corporation. Artificially low salaries trigger IRS scrutiny and reclassification. For the methodology and safe harbors, see How to Calculate and Document a Reasonable Salary for S-Corp Owners.

SE Tax and Partnerships / Multi-Member LLCs

General partners in a partnership (and members treated as general partners in a multi-member LLC) pay SE tax on their distributive share of partnership income from active business operations. Limited partners generally do not pay SE tax on their distributive share — only on guaranteed payments for services (IRC §1402(a)(13)). The general vs. limited partner distinction is frequently litigated; CPAs should carefully review LLC operating agreements and member roles before assuming SE tax exemption for a limited member who is actively involved in the business.

The "active partner" question for LLCs has been the subject of proposed Treasury regulations for decades, and the rules remain unsettled for LLCs with members who have both management authority and economic interest. Conservatively treating LLC members who provide substantial services as general partners (subject to SE tax) until regulations resolve the issue is the safer approach.

Related Terms

S-Corporation — the primary entity structure that eliminates SE tax on distributions above a reasonable salary
FICA tax — the employer-employee equivalent of SE tax; employees pay 7.65% and employers match it, while self-employed individuals pay both sides as SE tax
Additional Medicare Tax — the extra 0.9% on SE earnings above $200,000/$250,000, not offset by the half-deduction

How CPAs Use Self-Employment Tax Analysis in Practice

SE tax analysis appears in almost every engagement involving a business-owner client:

Entity conversion analysis: Modeling whether the SE tax savings from an S-Corp election exceed the associated compliance costs, calibrated to the client's specific income level and reasonable salary benchmark. For the full analysis, see How to Minimize Self-Employment Tax for High-Earning Business Clients.
Retirement plan optimization: SE income is also the basis for retirement plan contribution calculations. A higher net SE income base supports larger SEP IRA or Solo 401(k) contributions, creating a tradeoff: reducing SE tax by structuring as an S-Corp also reduces the earned income base for certain retirement plan contributions.
Gig economy clients: Self-employed clients earning income through platforms such as Uber, DoorDash, Airbnb, and similar services pay SE tax on net platform earnings regardless of whether they receive a Form 1099-K. Explaining the SE tax obligation at onboarding is one of the most common year-one surprises for new gig workers who previously only had W-2 income.