If you are self-employed with no full-time employees, understanding the solo 401(k) contribution limits can be the single biggest lever for cutting your tax bill and building retirement wealth. A solo 401(k) lets you save in two capacities at once — far more than a standard IRA allows.
A solo 401(k) lets you contribute as both employee and employer, so your total contribution combines an elective deferral plus an employer profit-sharing amount of up to 25% of compensation. The combined total is capped each year by an IRS overall limit that is indexed for inflation — verify the current 2026 figures on IRS.gov.
What is a solo 401(k)?
A solo 401(k), also called a one-participant 401(k) or individual 401(k), is a retirement plan designed for business owners with no employees other than a spouse. The IRS treats you as wearing two hats: the employee and the employer. That dual role is exactly why the plan is so powerful.
Because you contribute in both roles, you can typically set aside far more than you could with a SEP IRA or traditional IRA at the same income level. Coordinating these contributions is a core part of smart tax planning for the self-employed.
The two parts of a solo 401(k) contribution
Your total contribution is the sum of two distinct buckets. Understanding the difference is the key to maximizing the account.
- Employee elective deferral. As the employee, you can defer up to 100% of your compensation, up to the annual deferral limit set by the IRS. This is the same deferral cap that applies to corporate 401(k) employees.
- Employer profit-sharing (nonelective) contribution. As the employer, your business can contribute up to 25% of your compensation. For self-employed individuals, “compensation” means net earnings after deducting half of self-employment tax and the contribution itself, so a special calculation applies.
- Catch-up contribution. If you are age 50 or older, you can add an extra catch-up amount on top of the elective deferral. This sits outside the overall limit.
How the 2026 limits fit together
There are three separate numbers to track, and all three are adjusted annually for inflation. Do not rely on a fixed figure — confirm the current-year amounts on the IRS one-participant 401(k) page before you contribute.
| Limit | Who it applies to | How it works in 2026 |
|---|---|---|
| Elective deferral limit | You, as employee | Annual cap on your salary deferral — verify on IRS.gov |
| Catch-up (age 50+) | Older savers | Extra deferral on top of the limit — verify on IRS.gov |
| Overall contribution limit | Employee + employer combined | Total cap (excluding catch-up) — verify on IRS.gov |
| Employer share | Your business | Up to 25% of compensation |
Worked example: how the math stacks up
Imagine Maria, a 45-year-old freelance designer taxed as a sole proprietor. The figures below are illustrative to show the structure of the calculation — not current limits.
- Maria’s net self-employment earnings (after the SE-tax adjustment) are $120,000.
- As the employee, she defers the full elective deferral limit — verify the 2026 figure on IRS.gov.
- As the employer, she adds roughly 20% of her adjusted net earnings (the effective rate for a sole proprietor, equivalent to 25% of compensation).
- Her total contribution is the sum of both, capped at the overall annual limit.
The takeaway: because the employer piece is calculated on income Maria already earns, the solo 401(k) lets her contribute dramatically more than the IRA limit alone — while reducing her taxable income today.
Solo 401(k) vs. SEP IRA
Both plans suit the self-employed, but they behave differently. A SEP IRA only allows the employer contribution, while a solo 401(k) adds the employee deferral on top.
| Feature | Solo 401(k) | SEP IRA |
|---|---|---|
| Employee deferral | Yes | No |
| Employer contribution | Up to 25% of compensation | Up to 25% of compensation |
| Catch-up at 50+ | Yes | No |
| Roth option | Often available | Limited |
| Loans | Sometimes permitted | No |
| Setup complexity | Moderate | Simple |
For maximum contributions at lower-to-mid incomes, the solo 401(k) usually wins because the employee deferral stacks on top of the employer share. The SEP’s simplicity still appeals to some owners.
Roth solo 401(k) contributions
Many solo 401(k) plans offer a Roth bucket for the employee deferral. You give up the upfront deduction, but qualified withdrawals are tax-free. The employer profit-sharing portion is traditionally pre-tax, though recent law has expanded Roth employer options — check whether your plan supports it.
Deadlines and setup rules
Timing is where solo 401(k)s catch people out. Generally, the plan itself should be established by your business’s tax-filing deadline (including extensions), and the employee deferral election has its own timing rules. Employer contributions can usually be made up to the filing deadline plus extensions.
- Confirm both the plan-establishment deadline and the contribution deadline for your entity type.
- File Form 5500-EZ once plan assets exceed the IRS reporting threshold.
- Keep clear records of which contributions are employee versus employer.
Adding a spouse to your solo 401(k)
One overlooked advantage: a spouse who earns income from the same business can also participate, which effectively doubles the household’s contribution capacity within a single plan. Each spouse gets their own employee deferral, and the business can make an employer contribution for each. The spouse must be a legitimate employee or co-owner with reasonable compensation.
Frequently asked questions about solo 401(k) contribution limits
What are the solo 401(k) contribution limits for 2026?
For 2026, your total contribution combines an employee elective deferral plus an employer share of up to 25% of compensation, capped by the IRS overall limit. All three figures are indexed for inflation, so confirm the exact 2026 dollar amounts on IRS.gov before contributing.
Can I contribute to a solo 401(k) and another 401(k)?
Yes, but your employee elective deferrals are aggregated across all 401(k) plans you participate in, so the combined deferral cannot exceed the annual deferral limit. The employer contributions are tracked per employer. Coordinate carefully to avoid excess deferrals.
Can my spouse contribute to my solo 401(k)?
Yes. If your spouse earns income from the same business, they can participate as an employee and the business can make employer contributions for them too. This effectively doubles the household’s contribution capacity within the plan, provided the spouse receives reasonable compensation.
Does a solo 401(k) reduce self-employment tax?
Solo 401(k) contributions reduce your income tax but generally do not reduce self-employment tax, which is calculated on net earnings before retirement contributions. The deduction lowers your income tax bill rather than the Social Security and Medicare portion. Verify the current treatment on IRS.gov.
When must I set up a solo 401(k)?
Generally the plan must be established by your business’s tax-filing deadline, including extensions, with employee-deferral timing rules of their own. Employer contributions can often be made later. Deadlines vary by entity type, so verify your specific dates on IRS.gov.
Book a free consultation
The solo 401(k) is one of the most generous retirement vehicles available to the self-employed — but only if the deferral and profit-sharing math is calculated correctly and the deadlines are met. Tranzesta helps US and UK clients set up and fund these plans for maximum tax savings. Book a free consultation today.
Disclaimer: This article is for general informational purposes only and does not constitute tax, legal, or accounting advice. Tax rules and figures change and depend on your situation and tax year. Always verify current IRS figures and consult a qualified tax professional before acting.
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