Solo 401(k) vs SEP IRA Calculator

See the most you could contribute to each plan this year as a self-employed person with no employees, and why the Solo 401(k) usually allows more at lower profits.

United States · tax year 2026 · built by Aftab Ahmad · limits checked September 29, 2026 and monitored weekly against IRS sources

Your numbers

Net profit from self-employment (2026)

Schedule C profit, before retirement contributions.

Your age at the end of 2026

50+ adds a catch-up to the Solo 401(k); 60 to 63 adds a larger one.

Already deferred to another 401(k) this year

From a job's 401(k) or 403(b). The $24,500 deferral limit is shared.

Solo 401(k) maximum$39,369.64$24,500 more than a SEP IRA

SEP IRA maximum$14,869.64employer contribution only

How the maximums are calculated
1. Self-employment tax	on net profit, 2026 rates	$11,303.64
2. Compensation	profit − half of line 1	$74,348.18
3. Employer contribution	20% of line 2 (25% after the contribution)	$14,869.64
SEP IRA	line 3, up to $72,000	$14,869.64
4. Employee deferral	up to $24,500	$24,500.00
5. Catch-up	under 50: none	$0.00
Solo 401(k)	lines 3 + 4, up to $72,000 and your compensation, + line 5	$39,369.64

The formula

Compensation = net profit − half of your self-employment tax.
Employer contribution (both plans) = 20% of compensation, which is the IRS's 25% rate applied after the contribution itself. Compensation above $360,000 is not counted.
SEP IRA = the employer contribution, up to $72,000.
Solo 401(k) = an employee deferral of up to $24,500 (shared with any other 401(k) you contribute to) + the employer contribution, up to $72,000 and never more than your compensation.
Catch-up (Solo 401(k)): $8,000 from age 50, or $11,250 at ages 60 to 63, on top of the $72,000 limit.

It reproduces the worked examples in our guide Solo 401(k) vs. SEP IRA (for example, $80,000 of profit: $14,870 for a SEP and $39,370 for a Solo 401(k)), which also covers setup deadlines, Roth options and what changes if you hire staff.

Assumptions and limits

For a sole proprietor with no employees (a spouse may join a Solo 401(k)), with self-employment income only and no other employer plan for this business.
These are maximums, not recommendations. What you can afford, and whether traditional or Roth contributions suit you, matter more.
Contributions lower income tax but not self-employment tax, which is why the formula starts from profit before contributions.
It does not cover W-2 wages from your own S corporation, multiple businesses, or special rules such as Roth treatment of catch-up contributions for some higher earners with wages. Check your plan's rules.
Numbers you type stay in your browser; nothing is sent to us or stored.

An estimate for planning, not tax, investment or retirement advice. Confirm your contribution with your plan provider and IRS Publication 560, or with a CPA. This tool has not been reviewed by a licensed tax professional.

Sources

IRS: Publication 560, Retirement Plans for Small Business — the self-employed contribution formula, the $72,000 and $360,000 limits for 2026
IRS: 401(k) limit increases to $24,500 for 2026 — the deferral and catch-up limits
IRS: One-participant 401(k) plans — who can use a Solo 401(k) and how the two contribution roles work
IRS: SEP contribution limits — the SEP limit

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