Solo 401(k) Contribution Calculator
Your maximum Solo 401(k) contribution — the employee deferral plus the employer share — for a one-person business with no employees.
Your details
Rough figures are fine — you can refine later.
How we calculate this
We compute the maximum Solo 401(k) contribution for a sole proprietor with no employees.
1. Employee deferral. The annual elective-deferral limit from tax-constants.json, plus a catch-up if you're 50+. Ages 60–63 use the 2026 super-catch-up, which *replaces* the standard catch-up rather than adding to it.
2. Employer share. Net SE earnings (net profit minus the deductible half of SE tax) × 20%.
3. Cap. The two parts are limited to the overall §415 total (plus any catch-up).
Assumptions: sole proprietor, no employees, no S-corp election. This is a planning estimate, not tax advice — confirm with a CPA/EA.
Primary sources
- IRS Publication 560, Retirement Plans for Small Business
- IRS One-Participant 401(k) Plans
- IRS Retirement Topics — 401(k) and Profit-Sharing Plan Contribution Limits
The biggest legal shelter for a one-person business
If you're self-employed with no employees, a Solo 401(k) is usually the most you can legally shelter from tax in a single year. It works because you play both roles: you're the employee, who can defer a flat amount of salary, and the employer, who can add a profit-sharing contribution on top. Stack the two and the total dwarfs what a SEP or IRA alone allows.
Enter your net profit, age, and tax year. This calculator returns your maximum contribution, split into the employee and employer pieces, plus what it shelters as a share of profit.
The two contributions
Employee deferral. A flat dollar limit set each year, the same whether you earn $60,000 or $600,000 — you just need enough profit to cover it. If you're 50 or older, a catch-up raises it further.
Employer profit-sharing. 20% of your net self-employment earnings (net profit minus the deductible half of your SE tax) — the same base a SEP uses.
The two are added together and then capped at the overall §415 limit (plus any catch-up). At moderate incomes the cap rarely binds; the employee deferral is doing most of the work, which is exactly why the Solo 401(k) beats a SEP.
The 2026 super catch-up
Beginning in 2026, savers aged 60 to 63 get a larger catch-up — $11,250 — that replaces the standard $8,000 catch-up rather than stacking on top of it. Outside that four-year window, the ordinary 50-and-over catch-up applies. Enter your age and the calculator uses the correct one automatically; there's no way to claim both.
Solo 401(k) vs SEP IRA
Same employer 20%, but the Solo 401(k) adds the employee deferral — so at equal income it shelters more. The trade-off is a little more paperwork: once the plan balance passes a threshold, an annual Form 5500-EZ is required, and the plan must be established by year-end (though it can be funded later). If you want the largest possible deduction and don't mind that, the Solo 401(k) wins. Compare directly with our SEP IRA calculator.
What it does and doesn't do
Contributions cut your income tax and grow tax-deferred. They do not reduce self-employment tax, which is figured on net profit first. This tool assumes a sole proprietor with no employees and no S-corp election.
What this is
A planning estimate, not tax advice. Your exact limits depend on your full return and plan documents — confirm with a CPA or EA before contributing.
Common 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 your income and age.
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) vs SEP IRA? + −
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. If your goal is maximum tax-deferred saving, the Solo 401(k) is typically the winner — compare both with our SEP IRA calculator.
Does it lower my self-employment tax? + −
No. Contributions reduce income tax and grow tax-deferred, but they do not reduce self-employment (Social Security and Medicare) tax, which is calculated on net profit before retirement contributions.
Keep going
Prepared for tax year 2026. Every rate and cap on this page cites a primary IRS or SSA source. Estimates only — not tax or financial advice. — for planning purposes only, not tax, legal, or financial advice.