2026 Solo 401k Contribution Calculator

How Solo 401k contributions actually work

A Solo 401k (also called an Individual 401k or Self-Employed 401k) is the highest-limit retirement plan available to self-employed individuals with no full-time employees other than a spouse. Because you wear two hats — you are both the employee and the employer — you get to contribute in two separate ways, which is why the total contribution limit (up to $72,000 in 2026, or $83,250 with the SECURE 2.0 super catch-up) is so much higher than a SEP-IRA or Traditional IRA.

1. Employee deferral (the salary side)

The first contribution is the employee elective deferral. In 2026 you can defer up to $24,500 of your earned compensation, or 100% of compensation if it's lower. This is the same limit that applies to employees of any company sponsoring a 401k — it is per-person, not per-plan, so if you also have a W-2 day job with a 401k, your deferrals across both plans count against the single $24,500 cap. You can make this contribution as pre-tax, Roth, or a mix, depending on whether your provider supports a Roth Solo 401k option.

2. Employer profit-sharing (the business side)

On top of the employee deferral, your business contributes a profit-sharing amount. The formula depends on your business structure:

• Sole proprietors and single-member LLCs (taxed as a disregarded entity): up to 20% of net self-employment income, where net self-employment income is your Schedule C profit minus the deductible half of self-employment tax. The 20% comes from the algebraic equivalent of "25% of compensation" once you subtract the contribution itself from compensation.
• S-Corp and C-Corp owners: up to 25% of your W-2 wages from the corporation. Distributions and K-1 pass-through income do not count toward this calculation — only W-2 wages.
• Multi-member LLCs and partnerships: generally 20% of net earnings from self-employment after the guaranteed-payment and self-employment-tax adjustments.

Whichever bucket applies, the sum of employee deferral + employer profit-sharing cannot exceed the overall annual additions limit ($72,000 in 2026, before catch-ups). The maximum compensation that can be considered for the employer calculation is also capped at $350,000 in 2026.

3. Catch-up contributions (age 50, and the new 60-63 super catch-up)

If you are 50 or older, you can add a catch-up contribution on top of the standard employee deferral — $8,000 in 2026. The SECURE 2.0 Act introduced a higher "super catch-up" for participants aged 60-63 specifically: $11,250 in 2026, instead of the standard $8,000. At age 64+, you go back to the standard catch-up amount. SECURE 2.0 also requires that catch-up contributions made by higher-income earners (over $145,000 in prior-year wages, indexed) be designated Roth — a rule that applies to plans whose providers support Roth catch-ups.

Multi-year Solo 401k contribution limits

Use the table below to compare contribution limits across the last three tax years. If you're funding a prior-year contribution, reference the row for that year's tax filing.

Source: IRS Notice 2024-80 (2025 limits) and IRS Notice 2025-67 (2026 limits). The age 60-63 super catch-up was introduced by the SECURE 2.0 Act and first applied in 2025.

Contribution deadlines

Employee deferrals must be elected by December 31 of the tax year. The actual cash funding rules differ by entity: S-Corp owners need to have their elective deferral withheld through payroll by year-end, while sole proprietors typically have until their tax filing deadline to fund the deferral. Employer profit-sharing contributions can be made up to the tax-filing deadline including extensions — March 15 for S-Corps (or September 15 with extension) and April 15, 2027 for sole proprietors (or October 15 with extension) for the 2026 tax year. Many people are surprised they can still fund a prior-year employer contribution well into the next calendar year.

Common Solo 401k contribution mistakes

• Using gross revenue instead of net. The employer profit-sharing math is based on net self-employment income (after expenses and half of SE tax), not gross receipts.
• Forgetting that employee deferrals are aggregated across plans. If you have a W-2 day job with a 401k, those deferrals reduce how much you can defer in your Solo 401k.
• S-Corp owners using K-1 income for the calculation. Only your W-2 wages count for the 25% employer contribution — distributions don't.
• Missing the Form 5500-EZ filing. Once your plan balance exceeds $250,000 at year-end, you must file Form 5500-EZ, even if no contributions were made that year.
• Treating the Roth catch-up rule as optional. SECURE 2.0 mandates that high earners ($145,000+ in prior-year wages, indexed) make catch-up contributions on a Roth basis if their plan supports it.