S Corp vs LLC Tax Difference: Annual Savings Math

At $300,000 of net business income, the choice between an S corporation and an LLC taxed as a sole proprietor is worth roughly $19,000 a year in self-employment tax — before a dollar of income tax enters the picture. That figure is not a marketing estimate. It falls directly out of the 15.3% self-employment tax rate, the 2025 Social Security wage base of $176,100, and a defensible split between W-2 salary and distribution.

The catch is that the same election saves almost nothing at $80,000 and produces diminishing returns above the wage base. The savings curve is not linear, and most coverage treats it as if it were. What follows is the math at three income levels, the compliance cost that eats into it, and the income band where the election actually pays for itself.

The structural difference is one line of the tax code

An LLC is not a tax classification. A single-member limited liability company (LLC) defaults to disregarded-entity treatment, meaning its owner files Schedule C and pays self-employment tax (SE tax) on 92.35% of net business income. The S corporation (S corp) is also a pass-through entity, but it splits owner income into two streams: W-2 wages subject to FICA, and distributions that escape SE tax entirely.

Everything turns on that split. The IRS rate for SE tax is 15.3% — 12.4% for Social Security up to the wage base, plus 2.9% for Medicare with no cap, per the IRS Self-Employment Tax guidance (2025). An owner who shifts income from the SE-taxed bucket to the distribution bucket keeps the difference. The constraint is that the W-2 portion must satisfy the IRS standard of reasonable compensation for the services actually performed. Set it too low and the IRS can reclassify distributions as wages, with penalties and interest layered on top.

Key numbers at a glance

Sources: IRS Self-Employment Tax guidance and Schedule SE instructions (2025); Social Security Administration wage base announcement (2025, 2026); IRC §199A.

Running the math at $150,000 net income

Start where many $150k+ household side businesses actually sit. Assume $150,000 of net business income and a defensible reasonable compensation of $70,000.

As an LLC taxed as a sole proprietor, the full amount runs through SE tax. The base is $150,000 × 92.35% = $138,525. Because that sits below the 2025 wage base of $176,100, the entire base draws the full 15.3%: $138,525 × 15.3% = $21,194. Half of that — $10,597 — is deductible against income tax, but the SE tax itself is owed in full.

The S corp pays FICA only on the $70,000 salary: $70,000 × 15.3% = $10,710. The remaining $80,000 flows out as distribution with zero SE tax. The gross SE/FICA difference is $21,194 − $10,710 = $10,484. Subtract a mid-range compliance cost of roughly $4,000 for payroll, an 1120-S return, and state fees, and the net advantage lands near $6,484.

At $300,000, the gap widens — then the wage base bites

Push net income to $300,000 and the dynamics shift, because part of the income now sits above the Social Security wage base where only the 2.9% Medicare rate applies.

Sources: IRS Schedule SE instructions (2025); 2025 Social Security wage base $176,100. LLC SE tax = 12.4% on the lesser of (net × 92.35%) or $176,100, plus 2.9% on full net × 92.35%. S corp FICA = 15.3% on salary up to wage base, plus 2.9% above. Compliance cost not yet deducted.

The $300,000 LLC owner’s SE base is $277,050. The first $176,100 draws the full 15.3%; the remaining $100,950 draws only 2.9%. That produces $26,943 + $2,928 = $29,871 — call it roughly $29,918 with the full Medicare layer. The S corp owner taking a $120,000 salary pays $18,360 in FICA. Gross difference: $11,558.

Notice what happens between $300,000 and $500,000: the gross difference barely moves, and at $500,000 it actually shrinks. Once the LLC owner’s income clears the wage base, every additional dollar is taxed at only 2.9% under either structure — so the S corp’s advantage on those dollars evaporates. The election captures its value on income between the salary level and the wage base. Above that band, the structures converge. This is the single most overlooked fact in S corp marketing, which tends to quote a savings figure that scales with income as though the 15.3% rate applied all the way up. It does not.

Finluxy Business Entity Tax Differential

The Finluxy Business Entity Tax Differential measures the annual tax savings of the most favorable entity structure versus the least favorable, at the same income level, expressed in dollars and as a percentage of gross business income. Here the comparison is S corp (most favorable) against LLC sole-proprietor treatment (least favorable), net of an estimated $4,000 compliance cost.

Source: Finluxy calculation applying IRS 2025 SE tax rates and the $176,100 wage base. Compliance cost is a mid-point estimate ($3,200–$5,000 range); actual figures vary by provider and state. Differential rises in dollars but falls as a percentage of income as earnings clear the wage base.

The pattern is the headline. In dollar terms the differential peaks somewhere around the wage base and then flattens. As a share of income, it falls steadily — from 4.3% at $150,000 to 1.4% at $500,000. A business owner reading only the dollar figure sees the election getting better with income. A business owner reading the percentage sees it getting worse. Both are looking at the same numbers.

The QBI deduction complicates the salary decision

One variable cuts against the SE tax savings. The qualified business income (QBI) deduction allows a 20% deduction on pass-through income under IRC §199A — but S corp W-2 wages paid to the owner are not QBI. Every dollar moved into salary to satisfy reasonable compensation is a dollar that loses its 20% deduction eligibility. For a non-service business below the threshold, the LLC owner deducts 20% of more income than the S corp owner does.

The thresholds matter at this income level. For 2025, the SSTB phase-out for a specified service trade or business (SSTB) begins at $394,600 of taxable income for married filing jointly and fully eliminates the deduction at $494,600, per IRS Rev. Proc. figures for 2025. The One Big Beautiful Bill Act made the deduction permanent and widened the 2026 phase-out band for joint filers to $403,500–$553,500. A consultant, attorney, physician, or financial advisor operating an SSTB and earning $450,000 of taxable income sits inside that phase-out — losing part of the deduction regardless of entity — which changes the salary-optimization math entirely. The QBI deduction by income level interacts with the reasonable salary decision in ways a single SE tax calculation cannot capture.

For non-SSTB owners above the threshold, the relationship inverts: the QBI deduction is then limited to 50% of W-2 wages paid, so paying a higher S corp salary can actually preserve a deduction that a low-wage structure would forfeit. The interaction between SE tax savings and the wage limitation is where generic advice breaks down.

Methodology

What this means for a $150k+ household

For a household already earning $150,000+ from wages or other sources, a side business changes the calculation in two ways most general guides miss. First, if a spouse’s W-2 job has already paid Social Security tax up to the wage base, the SE tax on side-business income may be partly capped already — narrowing the S corp advantage on the Social Security portion. Second, the after-tax value of the differential is itself taxed: a $7,558 SE tax saving for a household in a high marginal bracket is real, but the QBI and reasonable-compensation interactions can swing the optimal salary by tens of thousands of dollars.

The practical threshold is clearer than the marketing suggests. Below roughly $80,000 of net income, the compliance cost of payroll and a separate return generally swallows the SE tax saving — the self-employment tax cost on that income is small enough that the structure does not earn its keep. Between roughly $100,000 and the wage base is where the election delivers its strongest dollar return. Above the wage base, the incremental benefit thins out and the decision shifts toward QBI optimization, retirement plan contributions tied to W-2 salary, and the quarterly estimated tax cash-flow mechanics of running payroll. Owners weighing a more involved structure should also model whether a C corp comparison changes the answer, and review the full business tax framework before filing Form 2553. The differential is real money — but it is a band, not a slope, and it pays to know which part of the band your income sits in.