A solo 401k calculator estimates how much a self-employed person or a one-owner S corporation can put into a one-participant 401(k) for 2026. Formula: Self-employed employer share = 20% × (net profit − ½ self-employment tax); total = deferral + catch-up + employer share, capped at $72,000 plus catch-up. A sole proprietor under 50 with $120,000 of net profit can defer $24,500 and add an employer share of about $22,304, for $46,804.45 in total.
On this page
How to use the solo 401k calculator
- Choose how you pay yourself: net self-employment profit from Schedule C, or W-2 wages from your own S corporation.
- Enter the net profit or the W-2 wages.
- Pick your age at year end: under 50, 50 to 59 or 64 and older, or 60 to 63.
- Enter the employee deferral you want to make, up to $24,500, or more if you are old enough for a catch-up. The catch-up is the part of your deferral above $24,500.
The solo 401k calculator then shows the deferral, catch-up, employer contribution and the total.
What formula does the solo 401k calculator use?
- Employee deferral: up to $24,500 in 2026, but not more than your compensation.
- Catch-up: $8,000 at age 50 or older, or $11,250 at ages 60 through 63.
- Employer share for W-2 wages: 25% of wages.
- Employer share for the self-employed: 20% of net profit after subtracting half of self-employment tax, which is the IRS rate-table result for a 25% plan rate.
- Total, before catch-up, cannot exceed $72,000, and compensation above $360,000 is ignored.
Solo 401k calculator worked example
Results from the solo 401k calculator for a sole proprietor and an S corporation owner:
| Situation | Deferral | Catch-up | Employer | Total |
|---|---|---|---|---|
| Net profit $120,000, under 50 | $24,500 | $0 | $22,304.45 | $46,804.45 |
| Net profit $120,000, age 55, deferring $32,500 | $24,500 | $8,000 | $22,304.45 | $54,804.45 |
| S corp W-2 wages $100,000, under 50 | $24,500 | $0 | $25,000 | $49,500 |
| Net profit $300,000, under 50 | $24,500 | $0 | $47,500 (cap) | $72,000 |
For the $120,000 sole proprietor, self-employment tax is about $16,955, half of it is $8,478, and 20% of the remaining $111,522 is $22,304.45.
Who can open a one-participant 401(k)?
The IRS describes a one-participant 401(k) as a plan covering a business owner with no employees, or the owner and a spouse. If you hire an eligible employee, you may have to cover that person, and the plan stops being a solo plan. Once plan assets pass $250,000 at year end, you generally file Form 5500-EZ.
The solo 401k calculator assumes you have no other employer plan. The $24,500 deferral limit is per person across every 401(k) and 403(b) you join, so if you also defer at a day job, subtract that amount from the deferral you enter.
Example: a consultant with a side business
Maria runs a consulting business with $90,000 of net profit and also works part time at a company where she defers $10,000 into its 401(k). Her personal deferral limit for 2026 is still $24,500 in total, so she can defer only $14,500 more in her solo plan. The employer share is separate and comes from her business: about $16,728. Entering $14,500 as the deferral gives a solo plan total near $31,228, which is the number she would plan around for the year.
2026 limits the calculator uses
All of the dollar figures come from IRS Notice 2025-67: the $24,500 deferral, the $8,000 catch-up, the $11,250 catch-up for ages 60 to 63, the $72,000 overall limit and the $360,000 compensation cap. The extra 0.9% Medicare tax is left out, so a high earner’s employer figure may be a few dollars high. Use the solo 401k calculator for planning, and confirm the exact figure on your return or with your plan provider.
Roth or pre-tax deferrals
Many solo plans allow Roth deferrals. The limit is the same; only the tax timing changes. A Roth deferral adds no deduction today, while a pre-tax deferral lowers this year’s income tax. Employer contributions are usually pre-tax unless your plan allows a Roth employer option, so check your plan document.
Estimates for education only, not tax, legal or financial advice. Check current rules with the tax authority or a qualified adviser.
Related converters and calculators
Related calculators:
- 401(k) calculator: growth projection
- Retirement calculator: savings target
- Self-employment tax calculator: SE tax
Sources
IRS: One-participant 401(k) plans; IRS Notice 2025-67: 2026 retirement plan limits; IRS: 401(k) limit increases to $24,500 for 2026; IRS Publication 560: Retirement plans for small business.
Questions about this calculator
What is the solo 401(k) limit for 2026?
The overall limit is $72,000, plus any catch-up. The employee deferral within it is $24,500.
How is the employer contribution figured if I am self-employed?
It is 20% of net profit after subtracting half of your self-employment tax.
What is the catch-up for ages 60 to 63?
$11,250 in 2026, instead of the $8,000 catch-up for other people age 50 or older.
Can my spouse join my solo 401(k)?
Yes. A spouse who works in the business can participate and has separate limits.
Do I need to file Form 5500-EZ?
Generally yes, once the plan holds more than $250,000 at the end of the year.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
Report a calculation issue