Solo 401(k) calculator for 2026

How the limit is worked out

• Your deferral — as the employee — up to $24,500 in 2026, as pre-tax or Roth, but not more than you earn.
• The business's contribution. For an S corporation, up to 25% of your W-2 salary. For a sole proprietor, 20% of net earnings — profit less the deductible half of self-employment tax — because the contribution reduces the earnings it's measured against.
• Together they can't pass $72,000, or 100% of your earnings. Pay above $360,000 isn't counted.
• Catch-up on top: $8,000 from age 50, or $11,250 for ages 60 to 63. If your wages from the business topped $150,000 the year before, the catch-up has to be Roth.

A SEP IRA has only the business's contribution — the same 25% or 20% — which is why a solo 401(k) allows more at almost every income below the point where both reach $72,000.

Two examples

• A sole proprietor with $100,000 of profit: net earnings about $92,900; the business can put in 20%, about $18,600, and the owner defers $24,500 — about $43,100 in a solo 401(k), against $18,600 in a SEP.
• An S corporation owner paid a $70,000 salary: 25% is $17,500 from the business, plus the $24,500deferral — $42,000, against $17,500 in a SEP. The company's profit above the salary doesn't count.

Things to know

• Employees change everything. A solo 401(k) is for a business with no eligible employees besides the owner and a spouse.
• The tax saving is on income tax. Pre-tax contributions don't reduce a sole proprietor's self-employment tax, or an S corporation owner's payroll tax on the deferral.
• Roth or pre-tax. Roth deferrals give no deduction now but come out tax-free later; the calculator's tax figure assumes pre-tax.
• Once the plan holds more than $250,000, it files a Form 5500-EZ each year.

Compare all the plans. How much to contribute, and whether Roth or pre-tax suits you, is a question for your CPA or financial advisor.