Solo 401(k) calculator: your max vs the SEP
Both plans share the same employer contribution. The Solo 401(k) stacks an employee deferral on top - this shows how much that's worth at 2026 limits, for your income and entity.
Sole props have no salary - all profit is yours. S-corps must pay a reasonable W-2 salary; the employer contribution uses that salary only, not owner distributions.
Profit for the year, before the employer contribution - round is fine.
Catch-up contributions only apply to the Solo 401(k) - the SEP has none.
Rough federal bracket, used only for the tax-deferred estimate. State not included.
- Employee deferral
- Catch-up (if any)
- Employer contribution
- Combined cap check
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How this works
- The employer side is the same formula for both plans: 25% of W-2 wages for an S corp, or 20% of net self-employment income (profit minus half the SE tax) as a sole proprietor. The SEP gets that and nothing else; the Solo 401(k) adds the employee deferral on top.
- The deferral is limited to your earned income, and the deferral-plus-employer total caps at $72,000 for 2026. Catch-ups sit outside that cap.
- Self-employment tax here uses the 2026 Social Security wage base ($184,500) and ignores the 0.9% additional Medicare tax above $200,000 - it shifts the employer number by a rounding error, not a decision.
- The Roth split, Form 5500-EZ past $250,000 in plan assets, and what happens when you hire W-2 employees are covered in the full Solo 401(k) vs SEP IRA comparison.
- Estimates for planning, not tax advice. Your accountant's numbers win.
Not financial, tax, or investment advice. New here? Read why we picked the complicated one, the self-employed benefits decision, or run the 529 numbers.