Solo 401(k) contribution calculator

Solo 401(k) math, plain English.

The Solo 401(k) has two contribution buckets that add together:

1. Employee elective deferral — same limit as a corporate 401(k) employee. $24,500 in 2026, plus an $8,000 catch-up if you're 50+ ($12,000 if 60-63 per SECURE 2.0). Limited to your wages or net SE earnings.
2. Employer profit-sharing — your business "matches" itself. For sole props / SMLLCs the effective rate is 20% of net earnings from self-employment (after the half-SE-tax deduction). For S-corp owners, it's 25% of W-2 wages.

Combined annual additions cap for 2026: $72,000 under 50, $80,000 if 50+ (including the catch-up).

The Solo 401(k) usually beats a SEP-IRA at any income up to about $300,000 because the employee-deferral bucket is added on top of the profit-sharing. Above $300k+ the two converge. See our Solo 401(k) vs SEP-IRA decision guide.

What you need to actually contribute.

• EIN required — you can't open a Solo 401(k) on your SSN, even if you're a sole prop. See our EIN vs SSN guide.
• Plan establishment deadline — by Dec 31 of the tax year for that year's elective deferral.
• Employer contribution deadline — extended return due date (typically Oct 15 of the following year).
• Form 5500-EZ filing — required once plan assets exceed $250,000.
• Roth Solo 401(k) — most modern providers (Fidelity, E*TRADE, Charles Schwab, Solo401k.com) offer a Roth option. Same deferral limit; pay tax now, withdraw tax-free.

This calculator shows the IRS maximum. Your provider may impose lower practical limits. Always confirm with a CPA before maxing out — especially if you have a W-2 job with another 401(k) (combined elective-deferral limit applies across all plans).

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