For S-Corp owners, the salary decision and the retirement contribution decision are the same decision. W-2 compensation isn't a free variable — it simultaneously determines Solo 401(k) contribution capacity, QBI deduction size, and annual payroll tax cost. Optimizing all three at once is what Tax Sherpa calls the S-Corp Retirement Stack. At $200k total income, the standard 2/3 salary / 1/3 distribution structure unlocks approximately $57,750 in combined Solo 401(k) contributions while preserving roughly $3,000–$4,000 in QBI benefit — a combination unavailable to anyone running these levers in isolation.

"It always seems to come back to somewhere very close to the Social Security cap for earnings that year. It is really just about Social Security taxes."

— Neal McSpadden, Founder, Tax Sherpa

Key Takeaways

• The S-Corp Retirement Stack is a three-lever optimization: W-2 salary, profit distributions, and Solo 401(k) contributions must be set simultaneously — changing one changes the other two.
• At $200k total S-Corp income, the 2/3 salary / 1/3 distribution structure produces roughly $57,750 in Solo 401(k) contributions (2026 limits) versus $33,250 from a SEP IRA — a gap of approximately $24,500.
• That gap is permanent: it equals the employee elective deferral ($24,500 in 2026), which the SEP IRA structurally cannot include. It is constant across every W-2 level below roughly $350,000.
• IRS reasonable compensation audit risk is almost entirely a Social Security wage base issue. When W-2 salary is near the SS cap ($184,500 in 2026), there is essentially no audit exposure — Tax Court history consistently resolves at approximately the SS cap.
• When total S-Corp income significantly exceeds the SS cap, the math flips: increasing the W-2 generates more retirement contribution room, and the additional Medicare tax cost (1.45% × 2, uncapped) is often worth paying.
• The employer Solo 401(k) match reduces net S-Corp profit, which slightly reduces the QBI base — but this recursive effect has never eliminated the QBI deduction in practice.
• Retirement is the last step of the S-Corp tax stack, not the first. Entity structure, accountable plan, and Summit Strategy Sessions deductions get optimized before the contribution number is set.

What Is the S-Corp Retirement Stack?

Most tax advice treats S-Corp salary strategy as one topic and retirement contributions as another. That framing produces bad results. For a business owner taking income through an S-Corp, the W-2 salary is the single lever that controls three outcomes at once:

1. Retirement contribution capacity — Solo 401(k) employer contributions are 25% of W-2 wages. A lower salary caps the employer match. A higher salary enables more, up to the compensation cap of $360,000.
2. QBI deduction size — The Section 199A qualified business income deduction flows through S-Corp profit, not W-2 wages. Every dollar shifted from salary to distribution preserves QBI eligibility.
3. Payroll tax cost — Social Security tax (6.2% employee + 6.2% employer) applies only up to the SS wage base ($184,500 in 2026). Medicare (1.45% × 2) has no cap. Salary decisions directly determine how much self-employment equivalent tax the S-Corp structure is saving.

The S-Corp Retirement Stack is the process of setting all three simultaneously — "two-thirds salary and one-third profit, plus the max Solo 401(k) contribution," in Neal's framing. It is not a formula to apply mechanically. It is an optimization with three moving parts, and the right answer changes materially above and below the Social Security wage base.