If you work for yourself, you can put money for retirement into a SEP IRA or a Solo 401(k) and deduct it. Both let you contribute as the “employer”, up to 20% of your net self-employment earnings. A Solo 401(k) also lets you contribute as the “employee”, up to $24,500 for 2026 plus catch-up if you’re 50 or older, so it usually allows much more at the same income. This calculator follows the IRS Publication 560 worksheet for a sole proprietor or single-member LLC and shows the most each plan allows. Everything runs in your browser and nothing is sent anywhere.

2026 net profit from self-employment (Schedule C line 31, or your share from Schedule K-1)
Your age at the end of 2026
W-2 wages from a job this year (Social Security wages, box 3)
401(k) or 403(b) deferrals you already make at a job this year
Your federal income tax bracket (%)
Plan's employer contribution rate (%, 25 is the most allowed)

How the math works

net SE earnings   = net profit x 92.35%
SE tax            = 12.4% x net SE earnings (up to $184,500 minus W-2 wages) + 2.9% x net SE earnings
earned income     = net profit - half of SE tax
employer limit    = earned income x 20%   (25% plan rate / 1.25), at most 25% x $360,000 and $72,000
SEP IRA max       = employer limit
Solo 401(k) max   = employer limit + employee deferral (up to $24,500, less deferrals at other jobs)
                    + catch-up ($8,000 at 50+, $11,250 at 60-63), never more than earned income
                    employer + deferral at most $72,000; catch-up goes on top

Example with the default inputs: $100,000 of profit gives $92,350 of net SE earnings and $14,129.55 of self-employment tax. Half of that ($7,064.78) comes off, so earned income is $92,935.22. The SEP IRA limit is 20% of that, $18,587.04. A Solo 401(k) allows the same $18,587.04 plus a $24,500 employee deferral, $43,087.04 in total, or $51,087.04 at age 50 to 59.

The rules this follows

  • Why 20% and not 25%. The plan rate is 25% of compensation, but for a self-employed person compensation is figured after subtracting the contribution itself, so the effective rate on earned income is 25% / 1.25 = 20% (Pub. 560 rate table). A plan with a lower rate gets a matching lower reduced rate.
  • 2026 limits. Total contributions (employer plus employee, not counting catch-up) are capped at $72,000. Employee deferrals are capped at $24,500, shared across every 401(k) and 403(b) you contribute to that year, including at a day job. Compensation above $360,000 doesn’t count. Catch-up is $8,000 at 50 or older, or $11,250 if you turn 60, 61, 62 or 63 in 2026. SEP IRAs have no employee deferral and no catch-up.
  • Who this fits. A Solo 401(k) is for a business with no employees other than you and your spouse. If you have eligible employees, a SEP IRA must give them the same percentage you give yourself, and a regular 401(k) has testing rules this calculator doesn’t cover. S corporation owners figure contributions on their W-2 salary instead of net profit.
  • Deadlines. SEP IRA contributions for 2026 can be made, and the plan can even be opened, until your tax filing deadline including extensions (April 15, 2027, or October 15, 2027 with an extension). For a Solo 401(k), employer contributions can also be made up to the deadline with extensions. A sole proprietor who opens a new Solo 401(k) after the year ends can still make first-year employee deferrals up to the original due date of the return, without extensions.
  • Traditional or Roth. The tax saving shown is for pre-tax (traditional) contributions. Roth contributions to a Solo 401(k) or SEP IRA count toward the same limits but give no deduction now.

Sources: IRS Publication 560, Retirement Plans for Small Business, IRS COLA table for 2026, IRS Notice 2025-67, One-participant 401(k) plans and Schedule SE. Figures checked on October 27, 2026. This is general information, not tax or investment advice.

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