Learn - What Is the Roth Solo 401(k) Limit?

If you’re self-employed and looking to build tax-free retirement wealth, the Roth Solo 401(k) is one of the most powerful tools available. But how much can you actually contribute to your Roth Solo 401(k) each year?

The answer depends on several factors—your business type, income level, and whether you’re contributing as the employee, employer, or both. Let’s break it down step-by-step.

Who’s Eligible to Open a Solo 401(k)?

To qualify for a Solo 401(k), you must:

Be self-employed or run a small business with no full-time W-2 employees other than a spouse.
Have earned income from active work or services (not passive income).
Operate under any business structure—sole proprietorship, S corporation, partnership, or LLC—as long as you perform material services.

You can exclude:

Part-time employees working under 1,000 hours per year.
Independent contractors (since they’re not W-2 employees).
Employees under age 21.
Union employees.

Roth Solo 401(k) Contributions: Employee vs. Employer

There are two main contribution types for your Solo 401(k):

Employee Contributions
- You can choose pre-tax (tax-deductible) or Roth (after-tax) employee contributions.
- Roth contributions grow tax-free, meaning all future gains and withdrawals in retirement are 100% tax-free (if qualified).
Employer Contributions (Profit Sharing)
- Traditionally, employer contributions were pre-tax only.
- Under SECURE Act 2.0, you can now make Roth employer contributions as well.
- This gives you the flexibility to build more tax-free retirement wealth.

Important: If you also participate in a 401(k) through a day job, your employee deferrals are combined across all plans. However, employer contributions are not aggregated—you can still make them in both plans.

Total Roth Solo 401(k) Contribution Limits for 2025

For tax year 2025, the overall Solo 401(k) contribution limit is:

$70,000 if under age 50
$77,500 if age 50 or older (includes $7,500 catch-up contribution)
$81,250 if between ages 60–63, thanks to the Super Catch-Up under SECURE 2.0

These limits apply to combined contributions (employee + employer), including Roth contributions.

The Mega Backdoor Roth Solo 401(k) Strategy

Want to go beyond the standard Roth limits? The Mega Backdoor Roth Solo 401(k) allows you to make voluntary after-tax contributions and then convert them to Roth within your Solo 401(k).

Example:
If you pay yourself $70,000 in W-2 wages from your S corporation, you can:

Contribute $70,000 as voluntary after-tax to your Solo 401(k).
Immediately convert that amount to your Roth Solo 401(k).

This effectively allows you to move $70,000 into the Roth bucket, even if you’ve already maxed out contributions to your employer’s 401(k) plan.

My Solo 401k Financial handles all required IRS reporting for these conversions, including Form 1099-R.

Claim the $1,500 Auto Contribution Credit

Here’s a bonus many business owners miss:
Solo 401(k) plans can qualify for a $1,500 Auto Contribution Credit under the IRS small employer startup credit program.

Available to new and existing Solo 401(k) plans from My Solo 401k Financial.
File Form 8881 to claim $500 per year for three years.
A dollar-for-dollar credit that can offset your business taxes.

Key Takeaways

You can contribute up to $70,000 to your Roth Solo 401(k) in 2025 (or more with catch-ups).
Employee Roth and Employer Roth contributions are both allowed.
Use the Mega Backdoor Roth to maximize tax-free growth.
Claim your $1,500 credit to reduce your costs.