S-Corp vs Sole Prop: Impact on Retirement Savings

A self-employed person choosing between an S-Corporation and a Sole Proprietorship usually focuses on payroll tax savings. The retirement-contribution side of the analysis is at least as important and often points the other direction.

The two contribution formulas

For employer-side retirement contributions (Solo 401(k) profit-sharing, SEP IRA):

• S-Corporation: employer contribution = up to 25% of W-2 wages paid to the owner-employee.
• Sole proprietorship or single-member LLC: employer contribution = up to ~20% of net self-employment earnings (technically: net SE earnings minus half of SE tax, then × 25% / 1.25 ≈ 20%).

Both are capped at the §415(c) $70,000 annual additions limit.

Worked example: $200,000 of profit

An owner has $200,000 of net business profit before retirement contributions. She maxes a Solo 401(k) employee deferral ($23,500) in either case.

Sole proprietor path:

• Net SE earnings: $200,000
• SE tax deduction (half of SE tax): roughly $14,130
• Net for retirement calc: $185,870
• Employer contribution: ~20% × $185,870 = $37,174
• Total retirement: $23,500 + $37,174 = $60,674

S-Corp path (with $80,000 reasonable W-2 wage):

• W-2 wage: $80,000 (subject to FICA)
• K-1 distribution: $120,000 (not subject to FICA — the S-Corp savings)
• Employer contribution: 25% × $80,000 = $20,000
• Total retirement: $23,500 + $20,000 = $43,500

The sole proprietor contributes $17,174 more to retirement. The S-Corp saves about $18,360 of FICA on the $120,000 of K-1 distribution (15.3% × $120,000, of which OASDI alone is 12.4% only up to the $176,100 wage base). The retirement-contribution loss roughly offsets the FICA savings — but only because the example uses a high (some might say aggressive) salary-to-distribution ratio.

The "reasonable compensation" constraint

An S-Corp owner must pay herself "reasonable compensation" under §3121 and a long line of cases including David E. Watson, P.C. v. United States, 668 F.3d 1008 (8th Cir. 2012). The IRS routinely audits S-Corps with low salaries and large distributions; reclassification means back FICA, penalties, and interest. The "reasonable" number is fact-specific but generally references compensation paid for similar services in the same industry.

Raising the W-2 wage closes the retirement-contribution gap but reopens the FICA bill. The sweet spot depends on the owner's age, the retirement-savings target, and the tolerance for IRS audit risk.

When the S-Corp wins for retirement

• When the owner's W-2 wage is set high enough (say, $200,000+) that the 25% calculation exceeds the sole-prop ~20% calculation in absolute dollars.
• When the owner already pays FICA on $176,100 of wages from another job — the FICA savings disappear and only the retirement math matters.
• When a cash-balance plan is layered on top — the W-2 wage is the cash-balance compensation base, so a higher W-2 directly drives a larger cash-balance contribution.

When the sole prop wins for retirement

• For most owners earning under $300,000, the sole-prop or single-member LLC produces a slightly larger maxed Solo 401(k) at lower administrative cost.
• When the owner wants to maximize the §199A QBI deduction (made permanent by OBBBA), the QBI calculation is sometimes more favorable for sole props in industries below the W-2-wage-limit threshold.
• When the owner has irregular income — sole-prop contribution adjusts year-by-year with profit; S-Corp salary should not.

Common mistakes

• Setting an S-Corp salary too low. The retirement contribution and the FICA audit risk both turn on the salary number. A $30,000 salary on $300,000 of profit is begging for an audit and forfeits most of the retirement savings.
• Forgetting that K-1 distributions don't count. Only W-2 wages drive the 25% employer contribution for an S-Corp. Distributions, even from the same business, do not.
• Comparing only payroll tax. The retirement-plan delta is usually larger than the FICA delta after the wage base is reached.
• Ignoring state tax. Some states (CA, NY) tax S-Corps differently from sole props. Entity choice has multi-axis consequences.

Sources

• Internal Revenue Code §401(c)(2), net earnings from self-employment definition (Cornell LII): law.cornell.edu/uscode/text/26/401
• IRS Publication 560, Retirement Plans for Small Business: irs.gov/forms-pubs/about-publication-560
• David E. Watson, P.C. v. United States, 668 F.3d 1008 (8th Cir. 2012), reasonable S-Corp compensation: law.justia.com/cases/federal/appellate-courts/ca8/11-1589
• Internal Revenue Code §1402, self-employment income: law.cornell.edu/uscode/text/26/1402
• IRS, "S Corporation Compensation and Medical Insurance Issues": irs.gov/businesses/small-businesses-self-employed

RetirementCheck101 asks for entity type in step 10 and applies the right formula. Explore the free educational tool.