About the Solo 401(k) Calculator
This solo 401(k) calculator estimates the maximum you can put into an individual (one-participant) 401(k) for tax year 2026. It splits the total into the three buckets the IRS allows: your employee elective deferral, any age-based catch-up contribution, and the employer profit-sharing contribution your business makes on your behalf.
It is for business owners with no full-time employees other than a spouse: freelancers, consultants, gig workers and single-member LLC or S-corp owners. Self-employed users enter net profit and the calculator deducts half of self-employment tax before applying the 20% employer rate; corporate owners enter their W-2 salary and get the 25% rate. For 2026 the employee deferral is $24,500, the catch-up is $8,000 at age 50+ (or $11,250 at ages 60–63), and employee plus employer money is capped at $72,000 (IRS Notice 2025-67); pay counted for the employer contribution is capped at $360,000.
If you also contribute to a 401(k) at a day job, enter those deferrals: the $24,500 employee limit is shared across all plans, while the employer limit applies separately to each unrelated employer. Limits are editable so you can re-run it when the IRS updates them.
With the default inputs, the maximum total solo 401(k) contribution is $52,380.57. Change any value above to recalculate instantly.
How to use the solo 401(k) calculator
- 1Choose self-employed or W-2 from your own corporation.
- 2Enter your net profit or salary and your age at year end.
- 3Add any 401(k) deferrals you made at another job this year.
- 4Review the deferral, catch-up and employer split and the total.
- 5Make the employee deferral election by year end and fund the employer share by your tax deadline.
Formula and method
A solo 401(k) combines two contribution types. As the employee you can defer up to the elective limit D, but never more than your earned income. As the employer your business can add a profit-sharing contribution of 25% of W-2 wages, or for self-employed owners 20% of net earnings E (net profit minus half of self-employment tax). Employee plus employer money cannot exceed the overall limit L, while catch-up contributions sit on top of L.
Self-employment tax is 15.3% of 92.35% of net profit, with the Social Security part capped at the wage base. The SEP comparison uses the same employer formula without the employee deferral.
- D
- Employee deferral limit ($24,500 in 2026)
- E
- Net earnings (profit − ½ SE tax) or W-2 wages
- L
- Section 415(c) overall limit ($72,000 in 2026)
Worked examples
Self-employed, $150,000 profit, age 45
Self-employment tax is $21,194.32, so net earnings are $150,000 − $10,597.16 = $139,402.84. You can defer the full $24,500 and your business can add 20% × $139,402.84 = $27,880.57, for a total of $52,380.57.
Age 55 with $80,000 profit
Net earnings after half of the $11,303.64 SE tax are $74,348.18. You defer $24,500, add the $8,000 age-50 catch-up, and the business contributes 20% of net earnings, $14,869.64 — about $47,370 in total, versus under $15,000 in a SEP IRA.
S-corp owner, $100,000 salary, age 61
At 61 the SECURE 2.0 super catch-up of $11,250 applies. The corporation contributes 25% of the $100,000 salary, $25,000, on top of the $24,500 deferral, for $60,750.
Frequently asked questions
What is the solo 401(k) contribution limit for 2026?+
Employee deferrals are capped at $24,500, and employee plus employer contributions at $72,000. Catch-up contributions of $8,000 (age 50+) or $11,250 (ages 60–63) can be added on top of the $72,000.
Who can open a solo 401(k)?+
Any business owner with self-employment income and no full-time employees other than a spouse. Employees who work under 1,000 hours a year can usually be excluded, though long-term part-time rules may apply.
Can I have a solo 401(k) and a 401(k) at my day job?+
Yes. The $24,500 employee deferral limit is shared between the plans, but the employer profit-sharing limit applies separately to each unrelated employer, so your side business can still contribute up to 20% of net earnings.
When is the solo 401(k) deadline?+
Employee deferral elections generally must be made by December 31. Employer profit-sharing contributions can be deposited up to your tax filing deadline, including extensions. New plans for sole proprietors can be opened up to the filing deadline for employer contributions.
Do I need to file Form 5500-EZ?+
Once your solo 401(k) assets exceed $250,000 at the end of a plan year, you must file Form 5500-EZ by the last day of the seventh month after the plan year ends. Smaller plans are exempt.
Can I make Roth solo 401(k) contributions?+
Yes, if your plan document allows it. Employee deferrals can be designated Roth, and SECURE 2.0 also lets plans allow Roth employer contributions, which are taxable in the year they are made.
Tax results are estimates based on published rules and simplified assumptions. They are not tax advice — check official guidance or a tax professional for your situation.