Easy Steps to Calculate Your Solo 401(k) Contribution Limits for 2025 and 2026

A Solo 401(k) is one of the most effective retirement plans available to self-employed individuals and owner-only businesses. It allows you to contribute both as an employee and as an employer, which can significantly increase how much you can save each year on a tax-advantaged basis.

That same flexibility is also what makes the rules confusing.

Contribution limits depend on income type, business structure, age, and IRS cost-of-living adjustments that change from year to year. This guide walks through the Solo 401(k) contribution rules for both 2025 and 2026, explains how to calculate your limits step by step, and highlights strategies that can help you maximize retirement savings without triggering excess contributions.

What Are the Solo 401(k) Contribution Limits for 2025 and 2026?

Solo 401(k) contributions are made in two parts:

1. Employee elective deferrals
2. Employer profit-sharing contributions

Both components count toward an overall annual limit set by the IRS. The combination of these two buckets is what makes the Solo 401(k) such a powerful retirement vehicle for business owners.

Solo 401(k) Contribution Limits Overview

Contribution Type	Age Group	2025 Amount	2026 Amount
Employee elective deferral	All ages	$23,500	$24,500
Catch-up contribution	Age 50+	$7,500	$8,000
Catch-up contribution	Age 60–63	$11,250	$11,250
Employer profit-sharing	All ages	Up to 25% of compensation	Up to 25% of compensation
Total combined limit	Under 50	$70,000	$72,000
Total combined limit	Age 50+	$77,500	$80,000
Total combined limit	Age 60–63	$81,250	$83,250

These totals represent the maximum amount that can be contributed across all Solo 401(k) contribution types for the year.

Employee Elective Deferral Limits

The employee elective deferral is the portion you contribute as the employee of your business.

• 2025 elective deferral limit: $23,500
• 2026 elective deferral limit: $24,500

If your Solo 401(k) plan allows it, these contributions may be made as traditional pre-tax contributions, Roth contributions, or a combination of both.

It is important to note that employee elective deferrals are aggregated across all 401(k) plans you participate in. If you also contribute to a 401(k) through another employer, your total deferrals across all plans cannot exceed the annual limit.

Catch-Up Contributions by Age

Catch-up contributions allow older business owners to save more as they approach retirement.

• Age 50 and older
  • 2025: $7,500
  • 2026: $8,000
• Age 60 through 63
  • 2025: $11,250
  • 2026: $11,250

Catch-up contributions are added on top of the standard employee deferral limit and increase your overall annual contribution ceiling.

Catch-Up Contributions and SECURE Act 2.0 Changes

Catch-up contributions allow older savers to accelerate retirement funding, but SECURE Act 2.0 significantly changes how catch-ups work beginning in 2026.

Roth-Only Catch-Up Rule Beginning January 1, 2026

Starting January 1, 2026:

• If you are age 50 or older
• And your prior-year wages exceeded $150,000
  (for 2026 contributions, this looks at 2025 wages)
• Then all Solo 401(k) catch-up contributions must be made as Roth contributions

This rule:

• Applies to 401(k) and Solo 401(k) plans
• Does not apply to employer profit-sharing contributions
• Uses a $150,000 wage threshold that is not indexed for inflation

This change makes plan design critical. Solo 401(k) plans that do not support Roth contributions may prevent eligible participants from making catch-up contributions beginning in 2026.

Employer Profit-Sharing Contribution Limits

Employer contributions are calculated separately from employee deferrals and are based on eligible compensation.

In most cases, the employer may contribute up to 25 percent of compensation, subject to the overall annual limit.

• Sole proprietors and single-member LLCs calculate this based on adjusted net earnings
• S-corporation owners calculate this based on W-2 wages

Employer contributions are tax-deductible for the business and often represent the largest portion of total Solo 401(k) contributions.

Total Solo 401(k) Contribution Limits by Age

When employee deferrals, employer contributions, and catch-ups are combined, the total contribution limits are:

• Under age 50
  • 2025: $70,000
  • 2026: $72,000
• Age 50 and older
  • 2025: $77,500
  • 2026: $80,000
• Age 60 to 63
  • 2025: $81,250
  • 2026: $83,250

These totals define the absolute ceiling for all contributions made to the plan for the year.

How Contribution Calculations Differ by Business Type

Sole Proprietors and Single-Member LLCs

For sole proprietors, contributions begin with Schedule C net profit. From there, you must:

1. Calculate self-employment tax
2. Deduct half of that tax
3. Subtract employee elective deferrals
4. Apply the effective employer contribution rate, which is approximately 20 percent of adjusted net earnings

Failing to deduct half of self-employment tax is one of the most common calculation errors and often leads to over-contributions.

S-Corporation Owners

For S-corporation owners, Solo 401(k) contributions are based entirely on W-2 wages.

• Employer contributions may be up to 25 percent of W-2 wages
• Employee deferrals follow the standard IRS limits

Because payroll drives contribution capacity, reasonable and well-documented compensation is essential.

Advanced Strategies to Maximize Solo 401(k) Contributions

Mega Backdoor Roth Solo 401(k)

A Mega Backdoor Roth strategy allows you to:

1. Max out employee elective deferrals
2. Max out employer profit-sharing contributions
3. Use remaining space under the total limit for after-tax contributions
4. Convert those after-tax funds to Roth

For example, in 2026, a participant under age 50 could potentially contribute up to $72,000 in total if income supports it. Any unused space after employee and employer contributions may be available for after-tax contributions, provided the plan allows it.

Spousal Solo 401(k) Contributions

If a spouse earns eligible compensation from the business, each spouse may participate in the Solo 401(k).

This can effectively double household retirement contributions while maintaining full tax advantages, as each spouse is subject to their own annual limits.

Contribution Deadlines to Know

• Employee elective deferrals must be withheld and deposited according to payroll timing rules
• Employer profit-sharing contributions are generally allowed up to the business tax filing deadline, including extensions
• Form 5500-EZ is required once plan assets exceed IRS thresholds

Understanding these deadlines allows business owners to manage cash flow while remaining compliant.

Final Thoughts

Solo 401(k) contribution rules offer unmatched savings potential, but they require careful calculation and up-to-date knowledge of IRS limits. With the correct 2025 and 2026 numbers in hand, business owners can confidently plan contributions, avoid excess contribution penalties, and take advantage of advanced strategies like Roth conversions and spousal planning.

Using a properly designed Self-Directed Solo 401(k) that supports Roth, after-tax contributions, and clear compliance reporting can make the process far easier and help ensure every dollar is working efficiently toward long-term retirement goals.