Solo 401k Calculator
Calculate your 2026 Solo 401k contribution using current IRS limits. Handles both sole proprietor (20% effective rate) and S-corp owner (25% W-2 rate) calculations, plus the SECURE 2.0 super catch-up for ages 60-63.
Last updated: April 2026 · Source: IRS 2026 retirement plan limits, SECURE 2.0 Section 109
Schedule C net profit
50+ = +$8,000 catch-up, 60-63 = +$11,250 super catch-up
2026 Solo 401k limits by age
| Age | Employee deferral | + Employer (25%) | Total cap |
|---|---|---|---|
| Under 50 | $24,500 | up to $47,500 | $72,000 |
| 50-59 | $32,500 | up to $47,500 | $80,000 |
| 60-63 (super catch-up) | $35,750 | up to $47,500 | $83,250 |
| 64+ | $32,500 | up to $47,500 | $80,000 |
Source: IRS 2026 retirement plan contribution limits; SECURE 2.0 Act Section 109 (super catch-up for ages 60-63).
Frequently asked questions
What is the 2026 Solo 401k contribution limit?
For 2026, Solo 401k contributions come in two parts. The employee salary deferral limit is $24,500 (up from $23,500 in 2025). The employer profit-sharing contribution is up to 25% of W-2 compensation or approximately 20% of net self-employment income. The combined total cannot exceed $72,000 for those under 50, $80,000 for ages 50-59 or 64+, or $83,250 for ages 60-63 (thanks to the SECURE 2.0 super catch-up). These limits come directly from IRS Section 415 and the 2026 cost-of-living adjustments.
How does Solo 401k compare to SEP IRA?
Solo 401k almost always beats SEP IRA for solo business owners. The reason: Solo 401k adds a $24,500 employee salary deferral on top of the 25% employer contribution, while SEP IRA only allows the 25% employer portion. Example: at $100,000 self-employment income, a SEP IRA caps you around $18,600 (20% effective). A Solo 401k gets you to $43,100 ($24,500 employee + $18,600 employer). Same tax treatment, but Solo 401k lets you save $24,500 more at lower income levels. The trade-off is slightly more paperwork — Solo 401k requires Form 5500-EZ once assets exceed $250,000.
Can I have a Solo 401k if I have employees?
Only if your only other employee is your spouse. A Solo 401k (also called "one-participant 401k" or "solo-k") is reserved for businesses with no common-law employees other than the owner and spouse. If you hire even one part-time W-2 employee who meets the plan's eligibility requirements, you must convert to a regular 401k plan — which has more paperwork, testing requirements, and potentially employer contribution obligations for the employees.
Does the Solo 401k allow Roth contributions?
Yes. You can make the $24,500 employee deferral as either pre-tax (traditional) or Roth — or split between both. Starting in 2026, SECURE 2.0 Section 603 requires catch-up contributions to be Roth for any participant who earned more than $145,000 in W-2 wages in 2025 (threshold rises to $150,000 for 2027). The IRS delayed enforcement to 2026. Most Solo 401k providers now support Roth employee contributions, but not all support Roth employer contributions (SECURE 2.0 authorized it but custodian adoption varies).
When is the Solo 401k contribution deadline?
The plan itself must be established by December 31 of the tax year (under SECURE Act rules, sole proprietors can establish a Solo 401k up until their tax filing deadline and still make employer contributions). Employee salary deferrals must be elected by December 31 but can be deposited through your tax filing deadline. Employer profit-sharing contributions can be made up until the tax filing deadline including extensions — typically October 15 of the following year for most self-employed filers.
How much can a 60-year-old contribute to a Solo 401k?
Ages 60-63 get a special "super catch-up" under SECURE 2.0. For 2026: employee deferral up to $24,500 + $11,250 super catch-up = $35,750 employee portion. Add the employer profit-sharing contribution of up to 25% of compensation, and the total cap is $83,250. At age 64+ the super catch-up drops back to the regular $8,000 catch-up, total limit $80,000. This 4-year window (60, 61, 62, 63) is one of the most generous retirement savings provisions in US tax law and is only available in workplace plans like 401k and 403b.
What counts as compensation for Solo 401k?
For S-corp owners, compensation is W-2 Box 1 wages (not distributions). This means S-corp owners must pay themselves a "reasonable salary" to contribute to a Solo 401k — higher wages allow higher contributions but also higher employment taxes. For sole proprietors, compensation is net self-employment income from Schedule C, reduced by the deductible half of self-employment tax. For 2026, the maximum compensation that can be counted is $360,000 (up from $350,000 in 2025). Income above that cap is ignored for the 25% employer calculation.
Can I take a loan from my Solo 401k?
Yes. Solo 401k plans allow loans up to 50% of the vested balance or $50,000, whichever is less. Loans must be repaid within 5 years (15 years if used to buy a primary residence) with interest at the prime rate plus 1-2%. This is a rare feature among retirement accounts — SEP IRAs and traditional IRAs do not allow loans. Loans can be useful for short-term business cash flow or emergencies, but borrowing from retirement is generally a last resort because it interrupts compound growth on the borrowed amount.
Do I need to file Form 5500 for my Solo 401k?
Only once your plan balance exceeds $250,000 at the end of the plan year. Below that threshold, no annual filing is required. Once you cross the threshold, you must file Form 5500-EZ each year. It is a relatively simple form compared to the full Form 5500, but it does add administrative burden. You must also file a final Form 5500-EZ when you close the plan, regardless of balance. Many Solo 401k providers offer filing assistance as part of their service.
What is the Mega Backdoor Roth with Solo 401k?
If your Solo 401k plan documents allow after-tax contributions and in-service distributions, you can contribute up to the full $72,000 (or $80K/$83,250) limit as after-tax, then immediately convert to Roth — the "Mega Backdoor Roth." Example: $24,500 employee + $18,600 employer + $28,900 after-tax → $72,000 total, with $28,900 ending up in a Roth. Not all Solo 401k providers support this — check before choosing. Fidelity's Solo 401k does NOT, but specialized providers like Mysolo401k.net and Rocket Dollar do.
How does Solo 401k affect my taxes?
Traditional (pre-tax) Solo 401k contributions are deductible from federal and state income tax, reducing your current tax bill. However, they do NOT reduce self-employment tax (the 15.3% Medicare/Social Security portion) — SE tax is calculated on your gross net earnings before any retirement contributions. Roth Solo 401k contributions provide no current deduction but grow tax-free for qualified withdrawals after 59.5. Most business owners in high tax brackets benefit more from traditional contributions during peak earning years and Roth contributions during lower-income years.
Can I contribute to Solo 401k and also a regular 401k at another job?
Yes, but the $24,500 employee deferral limit is PER PERSON, not per plan. If you have a W-2 job with a 401k AND a side business with a Solo 401k, your total employee deferrals across both plans cannot exceed $24,500 ($32,500 if 50+, $35,750 if 60-63). The employer profit-sharing limit is per plan, so you can still make the full 25% employer contribution on your Solo 401k business income. This stacking strategy is one of the most powerful ways for W-2 employees with side income to maximize retirement savings.
Data sources: IRS 2026 retirement plan contribution limits; SECURE 2.0 Act (2022); IRS Publication 560 (Retirement Plans for Small Business); Fidelity Solo 401k 2026 limits guide.
Last updated: April 2026. Solo 401k limits are updated annually by the IRS each November for the following tax year.
Disclaimer: This calculator provides estimates for educational purposes only and is not tax or financial advice. Self-employment retirement plan calculations depend on specific business structure and income type. Consult a CPA for personalized advice.