A Solo 401(k), also called an individual 401(k), is open to self-employed people with no employees other than a spouse. You contribute in two roles: as the employee, up to a fixed dollar limit, and as the employer, a share of profit. That combination usually shelters far more than a SEP IRA at the same income. This calculator applies the 2026 IRS limits, including the higher catch-up for ages 60 to 63.
Figures checked by Muhammad Ahmad against IRS: 2026 retirement plan limits (IR-2025-111), IRS: One-participant 401(k) plans and IRS Notice 2025-67. Prices and rules change, so confirm with the official source before relying on them. How we check the math
How it works
Net earnings from self-employment = Schedule C profit minus the deductible half of self-employment tax.
Employer share: 20% of net earnings, the same formula as a SEP IRA. Employee deferral: up to $24,500 for 2026, reduced by anything you already deferred to another 401(k) this year, and never more than the earnings left after the employer share.
The two together can't exceed $72,000. Catch-up contributions sit on top: $8,000 from age 50, or $11,250 if you are 60, 61, 62 or 63 at the end of the year.
The total can never exceed your net earnings, which is what limits contributions at lower incomes.
A worked example
With $120,000 of profit, net earnings after the self-employment tax deduction are $111,522. The employer share is 20% of that, $22,304, and the full $24,500 employee deferral fits on top, for $46,804. That is $24,500 more than a SEP IRA allows at the same profit. A 52-year-old could add the $8,000 catch-up for $54,804, and a 61-year-old the $11,250 catch-up for $58,054.
Questions people ask
What is the Solo 401(k) limit for 2026?
$72,000 of employee and employer contributions combined, plus catch-ups: up to $80,000 from age 50 and up to $83,250 for ages 60 to 63. The employee part alone is capped at $24,500.
Who can open a Solo 401(k)?
Self-employed people and business owners with no employees other than a spouse. Part-time or seasonal workers below the plan's hours threshold usually don't count, but check the rules for your plan.
I have a 401(k) at my day job. Can I still use a Solo 401(k)?
Yes, but the $24,500 employee deferral is shared across all your 401(k) plans. The employer share is separate, so you can still make it from your self-employment earnings.
When are Solo 401(k) contributions due?
Employee deferrals must be elected by the end of the year and the plan must generally exist by then; employer contributions can be made up to your tax filing deadline, including extensions. Plan providers set their own processing cut-offs.
Do I need to file anything for a Solo 401(k)?
Form 5500-EZ once plan assets exceed $250,000 at the end of a year, and in the plan's final year.