Solo 401(k) Contribution Calculator
Your maximum Solo 401(k) contribution — the employee salary deferral plus the 20% employer share — for a one-person business with no employees.
Written by Dorothy Ibrahim, 10+ years in banking & finance
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How we calculate this
This calculator finds the maximum Solo 401(k) contribution for a self-employed person with no employees. You play both roles: the employee, who defers a flat amount of salary, and the employer, who adds a profit-sharing contribution of 20% of net self-employment earnings. Stack the two — capped at the overall §415 limit — and the total usually dwarfs what a SEP IRA or a plain IRA allows. Enter your net profit, age, and tax year to see the maximum, split into its employee and employer pieces.
The formulas
- Employee deferral
- annual elective-deferral limit + catch-up (if age 50+)Ages 60–63 use the 2026 super-catch-up, which replaces — not stacks on — the standard catch-up.
- Employer profit-sharing
- (net profit − deductible half of self-employment tax) × 20%
- Maximum contribution
- min(employee deferral + employer share, §415 total + catch-up)The §415 total is $72,000 for 2026 and $70,000 for 2025, plus any applicable catch-up on top.
Worked example
- With the default $100,000 net profit for 2026 and age 40, the employee deferral is the full 2026 limit of $24,500 (no catch-up under age 50).
- The employer share is 20% of net SE earnings: net profit minus the $7,065 deductible half of SE tax is $92,935, and 20% of that is about $18,587.
- Adding the two pieces gives roughly $43,087 — well under the $72,000 §415 cap — which shelters about 43.1% of net profit.
Rates, benchmarks & sources
- 2026 elective-deferral limit ($24,500) and §415 total ($72,000). — IRS Notice 2025-67
- Retirement Plans for Small Business — employer contribution and net-SE-earnings computation. — IRS Publication 560
- Solo 401(k) rules for a business owner with no employees. — IRS One-Participant 401(k) Plans
Figures current as of 2026-07-02. See our methodology & editorial standards for how constants are versioned and verified.
What this tool doesn’t model
- It assumes a sole proprietor with no employees and no S-corp election; adding eligible employees or a W-2 salary changes the contribution math.
- It computes the maximum allowed, not a recommendation — you can defer less than the full amount.
- Contributions reduce income tax but do not reduce self-employment (Social Security and Medicare) tax, which is figured on net profit first.
- It is an educational estimate for planning, not tax advice — confirm your number and plan documents with a CPA/EA.
Frequently asked questions
How much can I contribute to a Solo 401(k)?
Two parts: an employee salary deferral up to the annual limit (plus a catch-up if you are 50 or older), and an employer profit-sharing contribution of 20% of your net self-employment earnings. The two together are capped at the overall §415 limit. This calculator adds them up for the income and age you enter.
What is the 2026 super catch-up?
Starting in 2026, savers aged 60 to 63 get a larger catch-up ($11,250) that replaces — not stacks on top of — the standard $8,000 catch-up. Outside that age band, 50-and-older savers use the standard catch-up. This tool applies the right one automatically based on the age you enter.
Solo 401(k) or SEP IRA — which shelters more?
At the same income the Solo 401(k) usually shelters more, because it layers an employee deferral on top of the same 20% employer contribution a SEP allows. A SEP is simpler to administer with no annual filing. If your goal is maximum tax-deferred saving, the Solo 401(k) is typically the winner — compare both with our SEP IRA calculator.
Does a Solo 401(k) lower my self-employment tax?
No. Contributions reduce income tax and grow tax-deferred, but they do not reduce self-employment tax, which covers Social Security and Medicare and is calculated on net profit before any retirement contribution. The benefit is income-tax deferral, not payroll-tax relief.