Solo 401(k) and SEP-IRA contribution calculator, 2026
Enter your numbers to see how much you could put away this year and an estimate of the federal tax it could save. It is a starting point: we confirm the exact figure before you contribute.
Prepared by Prem Tax and Accounting Corp. Last checked against official sources on October 9, 2026.
Estimate your 2026 contribution
How the estimate works
- Sole proprietor or single-member LLC: net profit, less half of your self-employment tax, times 20% gives the business contribution. For a solo 401(k) you add your own deferral of up to $24,500 (plus catch-up if you are 50 or older).
- S corporation owner: the business contribution is 25% of your W-2 salary, and your deferral can be up to $24,500 (plus catch-up) but not more than your salary.
- Limits: $72,000 in all for 2026, not counting catch-up, and no more than your pay. Pay above $360,000 does not count.
- Tax saved: the total contribution times your bracket. It does not include self-employment tax, which a retirement plan does not reduce, or state tax.
Deadlines for the 2026 plan year
| Plan | Set up by | Contribute by |
|---|---|---|
| SEP-IRA | Your tax return due date, including extensions | The same date. Sole proprietor: April 15, 2027 (October 15, 2027 if extended). S corporation: March 15, 2027 (September 15, 2027 if extended). |
| Solo 401(k), S corporation or partnership | December 31, 2026 | Employee deferrals through payroll in 2026. Business contribution by the return due date, including extensions. |
| Solo 401(k), sole proprietor with no employees (new plan) | December 31, 2026, or after year-end by April 15, 2027 (the filing deadline without extensions) | Business contribution by the return due date, including extensions (October 15, 2027 if extended). |
| SIMPLE IRA | The 2026 window (January 1 to October 1) has closed. For 2027, by October 1, 2027. | Each payroll |
| Defined benefit or cash balance | Before December 31, with an actuary | As the actuary sets, by the funding deadlines |
| Form 5500-EZ (solo 401(k) with $250,000 or more) | July 31, 2027 for a calendar-year plan |
We confirm the exact amount, the plan paperwork and the deadline for your situation. Book a 20-minute call.
Common questions
How accurate is the calculator?
It uses the 2026 limits and the standard formulas for the self-employed (about 20% of net earnings after half of self-employment tax) and for S corporation owners (25% of W-2 pay). It ignores other jobs, other plans and some details, so treat it as an estimate and confirm with us.
Why is the S corporation result different?
An S corporation owner's contribution is based on W-2 salary, not profit. A low salary can save payroll tax but lowers the retirement limit.
Does it include state tax savings?
No. Contributions can also lower state income tax in states that follow the federal deduction. Illinois taxes retirement contributions differently, so ask us.
What if I have a job with a 401(k) too?
The employee deferral limit of $24,500 applies across all your plans. If you defer at your job, reduce the employee part here by that amount.
Official sources
Let's talk about your taxes, your business, your plans.
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