HOW TO: Report Solo 401k Contributions on Tax Return - 1065/Partnership/K-1

Watch: Detailed explanation of how to report Solo 401(k) contributions for partnership businesses filing Form 1065

For self-employed individuals whose businesses are taxed as partnerships (filing Form 1065), understanding how to properly report Solo 401(k) contributions on your tax return is essential for maximizing retirement benefits while staying compliant with IRS regulations. Solo 401(k) plans offer some of the highest contribution limits available to self-employed individuals, but the reporting requirements vary depending on the type of contributions you make.

Understanding Solo 401(k) Benefits for Partners

A Solo 401(k) has the highest contribution limits of any defined contribution plan available to self-employed individuals. As the IRS explains, this is because you can make both employee and employer contributions when you’re self-employed. With the right plan, you can make:

Pre-tax contributions – These reduce your current taxable income
Roth contributions – These are made after-tax, with potential tax-free growth
Mega backdoor Roth contributions – These allow you to contribute even more to a Roth account through voluntary after-tax contributions

2025 Solo 401(k) Contribution Limits

Employee Contributions: $23,500 ($31,000 if age 50+, or $34,750 if age 60-63)
Total Contribution Limit: $70,000 ($77,500 if age 50+, $81,250 if age 60-63)
Employer contributions can be up to 20% of self-employment compensation

Reporting Different Types of Solo 401(k) Contributions

Contribution Type	Where to Report	Tax Treatment	Additional Reporting
Pre-tax Employee	Line 16 of Schedule 1 (Form 1040) Line 13 of K-1 (Code R)	Reduces current taxable income	None
Roth Employee	Not reported	After-tax; tax-free growth	None
Voluntary After-tax	Not reported	After-tax; used for Mega Backdoor Roth	None for contribution; Form 1099-R for Roth conversion
Pre-tax Employer	Line 16 of Schedule 1 (Form 1040) Line 13 of K-1 (Code R)	Deductible business expense	None
Roth Employer	Line 16 of Schedule 1 (Form 1040) Line 13 of K-1 (Code R)	Deductible for year made; taxable to employee in year of deposit	Form 1099-R in year of deposit

Reporting Pre-Tax Employee Contributions

When you make pre-tax employee contributions to your Solo 401(k) as a partner in a partnership:

These contributions reduce your taxable income for the year for which the contribution is made
They are reported on Line 16 of Schedule 1 of your Form 1040
They are also reported on Line 13 of your Schedule K-1 (Form 1065) using Code R
For 2025, you can contribute up to $23,500 as an employee, plus catch-up contributions if eligible

Example: If you receive $100,000 of self-employment compensation (i.e. line 14 of K-1 less one-half of self-employment tax) from your partnership and make a $20,000 pre-tax employee contribution, this amount would be reported on Line 13 of your K-1 using Code R, as well as on Line 16 of Schedule 1 of your Form 1040, reducing your taxable income to $80,000 (before other adjustments).

Reporting Roth Employee Contributions

For partners making Roth employee contributions:

These contributions are made with after-tax dollars and don’t reduce your current taxable income
For partnerships, there is no place to report Roth employee contributions on your tax return
The contribution shares the same limit as pre-tax contributions ($23,500 for 2025, or $31,000 if age 50+, or $34,750 if age 60-63)

Reporting Voluntary After-Tax Contributions (Mega Backdoor Roth)

Voluntary after-tax contributions are used for the “Mega Backdoor Roth” strategy:

Like Roth contributions, these do not reduce your current taxable income
For partnerships, there is no place to report these contributions on your tax return
The mega backdoor Roth is a two-step process:

Step 1: Make voluntary after-tax contributions to your Solo 401(k) – not reportable
Step 2: Convert these funds to either a Roth Solo 401(k) or a Roth IRA – reportable on Form 1099-R

Example: If you make a $30,000 voluntary after-tax contribution to your Solo 401(k) and then convert it to your Roth Solo 401(k), the initial contribution is not reported on your tax return. The conversion to Roth will be reported on Form 1099-R for the year in which the conversion occurs.

Reporting Employer Contributions

As a partner in a partnership, you can also make contributions to your Solo 401(k) as the “employer”:

Pre-Tax Employer Contributions

Reported on Line 16 of Schedule 1 of your Form 1040
Also reported on Line 13 of your Schedule K-1 (Form 1065) using Code R
Reduces your taxable income for the year for which the contribution is made

Roth Employer Contributions

Under SECURE Act 2.0, employer contributions can now be designated as Roth contributions. Per IRS Notice 2024-2:

Still reported as a deductible business expense on Line 16 of Schedule 1 of your Form 1040 for the year for which the contribution is made
Also reported on Line 13 of your Schedule K-1 (Form 1065) using Code R
Reported as taxable income to you (as the employee) for the year in which the contribution is deposited via Form 1099-R

Important Note on Roth Employer Contributions

When you make Roth employer contributions, a unique tax situation arises:

If you make a 2024 Roth employer contribution in 2025 (before your tax filing deadline), it will be:
- Tax-deductible on your 2024 return (reducing 2024 income)
- Taxable to you as income in 2025 (when the funds are deposited)
This creates a timing difference between when the tax deduction occurs and when the income is recognized

Form 1099-R Reporting for Roth Conversions

There are two situations where Form 1099-R comes into play for Solo 401(k) participants in partnerships:

Voluntary After-Tax to Roth Conversions: When you transfer funds from your voluntary after-tax Solo 401(k) to either a Roth Solo 401(k) or Roth IRA
Roth Employer Contributions: When employer contributions are designated as Roth contributions

In both cases, Form 1099-R must be issued by the plan administrator for the year in which the deposit or conversion occurs. My Solo 401k Financial provides this 1099-R as an optional free service (no additional charge) for those clients who request it in a timely fashion.

Contribution Deadlines for Partnerships

2024 Solo 401k Contribution Deadline for Partnership/LLC taxed as a Partnership (1065)

Setup Deadline

Contribution Type

Contribution Deadline

12/31/2024

All types:

Employee (Pre-tax & Roth)
Employer
Voluntary After-Tax (Mega Backdoor Roth)

3/17/2025 or 9/15/2025 if timely extension filed

3/17/2025

Employer
Voluntary After-Tax (Mega Backdoor Roth)

3/17/2025

9/15/2025, if timely extension filed

Employer
Voluntary After-Tax (Mega Backdoor Roth)

9/15/2025, if timely extension filed

Common Questions About Solo 401(k) Reporting for Partnerships

Can I make employee contributions from my personal checking account?

Yes. From a Solo 401(k) perspective, contributions can come from either your personal or business account, regardless of contribution type. Some tax advisors prefer employee contributions to come from personal accounts and employer contributions from business accounts for accounting clarity, but this is not a requirement from a Solo 401(k) perspective.

Do I need to report my Roth Employee Solo 401k contributions anywhere?

No. For partners in a partnership, there is no place to report Roth employee contributions on your tax return. Unlike pre-tax contributions, which reduce your taxable income and must be reported, Roth employee contributions are made with after-tax dollars and don’t need to be reported. Note: Roth Employer contributions are reported as tax deductible on the employer’s return for the year for which the contributions is made and taxable to the employee for the year in which the contribution is deposited.

What forms do I need for year-end reporting when I fund my Solo 401(k)?

Contributions to a Solo 401(k) are not reportable by the plan itself – there’s no equivalent to the Form 5498 used for IRA contributions. However, you still need to report pre-tax contributions on your personal tax return to receive the tax deduction. Additionally, Form 1099-R is required for reporting Mega Backdoor Roth conversions and Roth employer contributions.

Conclusion

Properly reporting Solo 401(k) contributions on your tax return as a partner in a partnership is essential for claiming tax benefits and staying compliant with IRS regulations. The reporting method varies based on whether you’re making employee or employer contributions and whether they’re pre-tax, Roth, or voluntary after-tax.

For partners in partnerships, the process involves:

Reporting pre-tax contributions (both employee and employer) on Line 16 of Schedule 1 of Form 1040 and Line 13 of K-1 (Code R)
No reporting requirement for Roth employee contributions
No reporting requirement for voluntary after-tax contributions, but Form 1099-R reporting for subsequent Roth conversions
Understanding the unique timing and reporting issues for Roth employer contributions

Disclaimer: This article is provided for educational purposes only and should not be construed as tax, legal, or investment advice. Please consult with your tax professional for guidance specific to your situation.