Solo 401(k) / SEP-IRA Contribution Calculator
Created by: Liam Turner
Last updated:
Estimate how much a self-employed worker may be able to contribute under a Solo 401(k) or SEP-IRA using compensation, age, business type, and other-plan deferrals.
Solo 401(k) / SEP-IRA Contribution Calculator
FinanceCompare self-employed retirement-plan contribution ceilings using business type, compensation, age, and any deferrals already used elsewhere.
What is a Solo 401(k) / SEP-IRA Contribution Calculator?
A Solo 401(k) and SEP-IRA contribution calculator estimates how much a self-employed worker may be able to contribute under each plan type for the current tax year.
It is designed to make the contribution ceiling easier to compare.
This matters because self-employed retirement-plan rules are not intuitive.
Business structure, age, and whether you already defer into another 401(k) can materially change the result.
A useful calculator therefore estimates employee deferrals, catch-up room, employer contributions, and the total contribution ceiling rather than showing only one number.
How the Self-Employed Contribution Estimate Works
The calculator starts with the compensation base allowed for the selected business type.
It then estimates the employee-deferral room still available after any deferrals already made elsewhere.
Next it calculates the employer-contribution side and applies the annual overall limit.
That makes it possible to compare a Solo 401(k) ceiling with the SEP-IRA alternative using the same income inputs.
Core contribution ideas used
Solo 401(k) limit can include employee deferral + employer contribution + possible catch-up
SEP-IRA limit relies on the employer-contribution formula only
Other-plan elective deferrals reduce the remaining employee-deferral room in a Solo 401(k)
Example Scenarios
Example 1: Moderate self-employment income
At moderate income levels, the employee-deferral feature can make a Solo 401(k) materially more powerful than a SEP-IRA.
Example 2: High-income S-corp owner
At higher compensation levels, both plans may approach the annual ceiling, which shifts the decision toward features and admin rather than raw limit.
Example 3: Already contributing at a day job
A worker with another employer 401(k) may have limited deferral room left, which narrows the Solo 401(k) advantage.
How People Use This Calculator
- Estimate current-year retirement contribution room before filing.
- Compare Solo 401(k) and SEP-IRA ceilings side by side.
- See whether another employer plan reduces remaining Solo 401(k) deferral space.
- Model how business structure changes the compensation base.
- Use contribution capacity as the first step in plan selection.
Tips for Better Self-Employed Plan Selection
Check both plan rules and contribution room.
The highest limit is not always the best fit once setup deadlines, employee eligibility, or Roth features are considered.
Also verify the business-type inputs carefully.
The math for self-employment income and W-2 compensation is not interchangeable.
Frequently Asked Questions
What does a Solo 401(k) / SEP-IRA calculator estimate?
A Solo 401(k) / SEP-IRA calculator estimates maximum retirement-plan contributions for self-employed workers based on business income, business type, age, and other-plan deferrals.
Why can a Solo 401(k) allow a higher contribution than a SEP-IRA?
A Solo 401(k) can allow both an employee deferral and an employer contribution, while a SEP-IRA relies on the employer contribution formula alone. That often creates a higher ceiling, especially at moderate income levels.
Why does other-plan deferral matter?
Employee elective-deferral limits apply across plans, not separately to each 401(k). If you already defer into another employer plan, it reduces what may still be available in the Solo 401(k).
Why does business type affect the formula?
The contribution math is different for self-employed income and for S-corporation W-2 wages. That changes the compensation base used for the employer contribution.
Should I pick a plan based on contribution limit alone?
No. Contribution room matters, but so do setup rules, filing requirements, employee eligibility, Roth features, and administrative complexity.
Sources and References
- IRS materials on one-participant 401(k) plans and elective-deferral limits.
- IRS guidance for self-employed retirement plans including SEP contribution rules.
- Retirement-planning references on contribution ceilings and catch-up contributions.
Planning Note
Solo 401(k) / SEP-IRA Contribution Calculator is a planning estimate. Social Security records, pension plan terms, tax treatment, market returns, and retirement-account rules can all change the real-world outcome.