Self-Employment Tax 2026:
The 15.3% Math, Line by Line
Self-employment tax is the single largest federal tax cost for most sole proprietors and single-member LLC owners. The mechanics are unfamiliar to most people because they show up only when you stop being a W-2 employee and start running your own business. This page explains exactly how SE tax is computed, where it shows up on Form 1040, and the only legitimate way to reduce it.
The Formula in Plain English
SE tax = 15.3% x (92.35% of net business profit), capped on the Social Security portion at the annual wage base. For 2026 the wage base is $168,600 per the Social Security Administration announcement in October 2025. Above the wage base, only the 2.9% Medicare portion continues. Above $200,000 net earnings single or $250,000 joint, an additional 0.9% Medicare surtax applies. You can deduct one-half of SE tax on Form 1040 Schedule 1 as an above-the-line adjustment.
The 92.35% factor is the IRS's way of approximating the employer-half-of-FICA-not-subject-to-Social-Security-tax. The numbers below show how the formula plays out at various income levels.
SE Tax at Six Income Levels (2026)
| Net Profit | SE Base (92.35%) | SS portion (12.4%) | Medicare (2.9%) | Total SE Tax | 1/2 SE Deduction |
|---|---|---|---|---|---|
| $25,000 | $23,088 | $2,863 | $670 | $3,533 | $1,766 |
| $50,000 | $46,175 | $5,726 | $1,339 | $7,065 | $3,533 |
| $75,000 | $69,263 | $8,589 | $2,009 | $10,598 | $5,299 |
| $100,000 | $92,350 | $11,451 | $2,678 | $14,130 | $7,065 |
| $168,600 | $155,706 | $19,308 | $4,515 | $23,823 | $11,912 |
| $200,000 | $184,700 | $20,908 | $5,356 | $26,264 | $13,132 |
Above the $168,600 wage base the Social Security portion stops growing; only the 2.9% Medicare portion continues, plus the 0.9% additional Medicare surtax above the $200K / $250K thresholds. This is why high-income sole proprietors face a noticeably lower marginal SE tax rate on income above the wage base (about 3.8% for high earners) than on income below it (about 14.1% effective after the half-deduction).
Schedule SE Line-by-Line
Schedule SE is the IRS form that computes self-employment tax. Part I is the standard computation; Part II is the optional methods for low-income or farming taxpayers. For most sole props and LLC members, only Part I applies.
Line 2 captures net profit from Schedule C (most sole prop and SMLLC business income). Line 4a multiplies by 92.35% to get the SE income base. Line 7 caps the Social Security portion at the wage base ($168,600 for 2026). Line 8 contemplates W-2 wages from outside the SE business; if the taxpayer also has W-2 wages near or above the Social Security wage base, the SE portion that would push total earnings above the cap is excluded. Line 10 multiplies the SS-capped base by 12.4%. Line 11 multiplies the full SE base by 2.9% for Medicare. Line 12 totals lines 10 and 11. Line 13 computes the deduction for one-half SE tax, which flows to Form 1040 Schedule 1 line 15.
For taxpayers with significant W-2 wages already maxing out Social Security, this means SE income above the W-2 wage shortfall faces only the 2.9% Medicare portion of SE tax. A consultant with $200K of W-2 wages from a day job and $50K of side-consulting income would compute Schedule SE with the SE base reduced to only the Medicare portion (Social Security already maxed by W-2 wages), resulting in roughly $1,400 in SE tax on the $50K side income instead of about $7,000. This is one of the rare structural breaks for high-W-2 earners with side businesses.
The Additional Medicare Tax (0.9%)
The Affordable Care Act added an additional 0.9% Medicare tax on high earners, effective 2013, codified in IRC Section 3101(b)(2) for wages and IRC Section 1401(b)(2) for self-employment income. The tax applies to combined Medicare wages and self-employment income above $200,000 single or $250,000 married filing jointly. Unlike most income tax thresholds, these thresholds are not indexed for inflation, so they have become bindingly low for more taxpayers over time.
For self-employed taxpayers, the additional Medicare tax is computed on Form 8959 and added to Schedule 2 line 13 of Form 1040. The tax stacks on top of the regular 2.9% Medicare tax in the SE tax computation, making the marginal Medicare rate effectively 3.8% for high-earning self-employed taxpayers. There is no employer share to deduct on this portion (unlike the regular SE tax half-deduction).
The 3.8% Net Investment Income Tax (NIIT) under IRC 1411 is a separate tax that applies to investment income (interest, dividends, capital gains, rental income from passive activities) above the same thresholds. NIIT does not apply to self-employment income or to active-business pass-through income, but it does apply to certain passive-investor LLC income. The interaction of SE tax, additional Medicare tax, and NIIT for high-income business owners with mixed active and passive income gets complex; a tax professional should review the structure annually.
The S-Corp Election: The Only Legitimate SE Tax Reduction
For self-employed taxpayers with consistent net profit, the S-Corp election is the only well-established way to legitimately reduce SE tax. The mechanism: an LLC (or eligible corporation) that has elected S-Corp tax treatment via Form 2553 pays the owner partly as W-2 wages (subject to FICA, which is the corporate-employer equivalent of SE tax at the same combined 15.3% rate) and partly as distributions (not subject to FICA or SE tax). The distribution portion saves the 15.3% SE tax that would otherwise apply.
The salary must be "reasonable" by reference to comparable market wages for the role. The IRS has won numerous cases against S-Corp owners who paid themselves nominal salaries ($10K-$30K) on six-figure business profits, with the courts restating the salary upward and assessing back FICA plus penalties. Defensible benchmarks include Bureau of Labor Statistics Occupational Employment Statistics (OES), Robert Half salary surveys, or industry-specific compensation studies. A defensible documentation file at the entity level is important if the election is ever audited.
The break-even on the S-Corp election is roughly $40K-$60K of net profit in low-cost states (after accounting for payroll software, 1120-S preparation, and additional accountant time), and $60K-$80K in higher-cost states like California where the $800 minimum franchise tax adds to the overhead. Below these break-even points the election costs more than it saves. We cover full break-even math by state and income level on our S-Corp election page.
Things That Do NOT Reduce SE Tax
A short list to head off the most common misconceptions:
Forming an LLC by itself. SMLLCs pay SE tax identically to sole props.
Maximising retirement contributions. Solo 401(k) and SEP-IRA contributions reduce income tax but not SE tax. The SE tax is computed before retirement deductions.
Hiring family members. Wages paid to family employees are deductible business expenses (reducing net profit and thus SE tax), but the family members then owe SE tax or FICA on their own income, generally a wash or a net loss depending on circumstances.
Forming a Wyoming or Nevada LLC. Out-of-state formation does not change federal SE tax mechanics. The SE tax follows the taxpayer regardless of LLC state.
Paying yourself a salary from a sole prop. A sole proprietor cannot pay themselves a salary; draws are not deductible business expenses. The salary mechanism requires an entity (S-Corp election in LLC, or true C-corp).
Deducting personal expenses through the business. Personal expenses are not deductible regardless of structure, and trying to deduct them creates audit exposure and potential fraud liability.