Solo 401k Contribution Calculator

Calculator Inputs

Tax year

Business type

Owner age at year end

Owner net profit or W-2 pay

Owner deferrals at other jobs

Owner desired employee deferral Use 0 for maximum.

Owner Roth part of employee deferral

Spouse age at year end

Spouse net profit or W-2 pay

Spouse deferrals at other jobs

Spouse desired employee deferral Use 0 for maximum.

Spouse Roth part of employee deferral

Include spouse calculation

Treat catch-up as Roth when required

Formula Used

The calculator separates employee and employer roles. Regular employee deferral room equals the annual deferral limit minus deferrals already made to other plans. Catch-up room is added when age allows it.

For a corporation, employer profit sharing is estimated as 25% of eligible W-2 compensation. For a sole proprietor, employer profit sharing is estimated as 20% of adjusted earned income.

Sole proprietor adjusted earned income equals net profit minus one-half of estimated self-employment tax. Estimated self-employment tax uses 92.35% of net profit, Social Security tax up to the wage base, and Medicare tax on the same base.

Total regular additions cannot exceed the annual additions cap or eligible compensation. Catch-up deferrals are shown separately because they may be allowed above that cap.

How to Use This Calculator

Select the tax year and business type.
Enter owner age and net profit or W-2 pay.
Add deferrals already made through other workplace plans.
Enter desired employee deferral, or enter 0 for maximum.
Add Roth deferral amounts when your plan allows Roth contributions.
Check spouse calculation only when the spouse has eligible income.
Submit the form and review the result above the form.
Download the CSV or PDF report for your records.

Example Data Table

Example	Age	Business type	Income	Eligible compensation	Employee deferral	Employer contribution	Total
Example A	42	Sole proprietor	$120,000.00	$111,522.27	$24,500.00	$22,304.45	$46,804.45
Example B	55	Sole proprietor	$190,000.00	$176,576.93	$27,500.00	$35,315.39	$62,815.39
Example C	61	Corporation	$260,000.00	$260,000.00	$35,750.00	$47,500.00	$83,250.00

Solo 401k Contribution Guide

A solo 401k can help a self-employed owner save more than many basic plans. It works because the same person may contribute in two roles. The first role is employee. The second role is employer. This calculator separates those parts, so the limit is easier to review.

Employee Deferral

The employee deferral is the salary reduction part. It can be pretax or Roth, when the plan allows Roth. The annual elective limit applies across most plans. If you already used part of that limit at another job, enter that amount. The calculator subtracts it before finding your remaining room.

Employer Profit Sharing

The employer part is often called profit sharing. For a corporation, it is commonly capped at twenty-five percent of eligible W-2 pay. For a sole proprietor, the practical rate is often twenty percent of adjusted earned income. The adjustment reflects the deduction for one-half of self-employment tax. This file estimates that tax, then applies the plan limit.

Catch-Up Planning

Age matters. A participant who is at least fifty can add catch-up deferrals. Some ages may have a larger catch-up amount under current rules. Catch-up money is generally added above the annual additions cap. That is why the calculator shows regular deferral and catch-up deferral separately.

Using the Result

Start with the tax year. Then choose the business type. Enter income before plan contributions. Add other workplace deferrals, if any. Use zero in the desired deferral field when you want the maximum available amount. Enter a Roth amount only when part of the employee deferral should be after-tax. The final total combines employee, catch-up, and employer pieces.

Important Notes

This tool is for planning. It does not replace payroll, plan document, or tax advice. Final numbers can change because of business deductions, payroll timing, ownership rules, controlled groups, and plan terms. Use the CSV or PDF report to save your assumptions. Then review the result with a qualified adviser before funding the account.

Spouse Option

A spouse who earns income from the same business may have a separate account. That person needs their own compensation and limits. Enter spouse figures only when your plan covers them and records support the pay or earned income well.

FAQs

What is a solo 401k?

It is a retirement plan for a business owner with no common-law employees, except a spouse when allowed. The owner can contribute as employee and employer.

Does this calculator handle catch-up contributions?

Yes. It checks the participant age and applies the regular catch-up limit or the larger age 60 to 63 catch-up limit when available.

Why is the sole proprietor employer rate 20%?

Self-employed contributions need a special computation. A 20% rate is commonly used after adjusting net earnings for one-half self-employment tax.

Can I include my spouse?

Yes, when your spouse earns eligible income from the business and the plan covers the spouse. Enter separate spouse income and deferral details.

Are Roth deferrals deductible?

No. Roth employee deferrals are after-tax. The estimated deduction includes pretax employee deferrals and employer contributions only.

What if I also have a job with another plan?

Enter employee deferrals already made elsewhere. The employee deferral limit applies by person, not by each separate plan.

Does catch-up count against the annual additions limit?

Catch-up deferrals are generally shown above the regular annual additions cap. This is why the result separates regular deferral and catch-up used.

Is this final tax advice?

No. It is a planning estimate. Confirm final contributions with your plan provider, payroll records, tax return, and qualified adviser.