Thinking about setting up a Solo 401k for the 2025 tax year? Or do you already have one and need to meet all the deadlines? Either way, staying on top of key dates can help you maximize contributions and avoid potential penalties.
Below, you’ll find every important deadline for setting up your plan, making contributions, and filing IRS forms.
📝 Important: Filing dates may be subject to change, be sure to check the IRS website to confirm the latest information before filing. As always, working with a tax pro can be helpful in ensuring proper filings.
| What’s Due? | Deadline |
| Solo 401k Plan Setup | December 31, 2025 (for most businesses) |
| Employee Contribution Election | December 31, 2025 (for most businesses) |
| Form 945 | February 2, 2026 (February 10, 2026 if deposits were made on time and in full) |
| Form 1099-R (Paper Filing) | March 2, 2026 |
| Form 1099-R (E-filing) | March 31, 2026 |
| Contribution Deadline (S Corps, Partnerships, LLCs taxed as S Corps/Partnerships) | March 16, 2026 (September 15, 2026 if extended) |
| Contribution Deadline (C Corps, Sole Proprietorships, LLCs taxed as Sole Proprietorships) | April 15, 2026 (October 15, 2026 if extended) |
| Form 8606 | April 15, 2026 |
| Form 5500-EZ | July 31, 2026 (If using calendar year) |
| Extended Contribution Deadline | Sept 15, 2026 (S Corps, Partnerships, LLCs taxed as S Corps/Partnerships) Oct 15, 2026 (C Corps, Sole Proprietorships, LLCs taxed as Sole Proprietorships) |
December 31, 2025
Deadline to Set Up a Solo 401k Plan
(If you don’t already have one)
If you don’t have a Solo 401k plan, are eligible and want to contribute for the 2025 tax year, you must establish a plan by December 31, 2025. To understand eligibility, read our article about Solo 401ks.
Deadline to Make an Election
(If you wish to make employee contributions for the 2025 tax year)
To contribute employee salary deferrals to your Solo 401k, you need to make an election by December 31, 2025. A Solo 401k election is a formal written declaration stating:
- How much you plan to contribute as an employee
- Whether it goes into a pre-tax or Roth account
Since you’re both the employer and employee, this is essentially a signed and dated note to yourself for your records just in case the IRS requests it. You don’t need to deposit money into your Solo 401k yet, but you must have the election documented.
Exception for Sole Proprietors
If you run your business as a sole proprietorship, the SECURE 2.0 Act gives you more time to set up a Solo 401k and make your first elective deferrals.
For 2023 and later, a sole proprietor with no employees may be able to adopt the plan after year-end, as long as the plan is adopted by the tax filing deadline without extensions. For the 2025 tax year, that deadline is April 15, 2026.
📝 Important: Extensions do not apply to this special sole proprietor rule. For the 2025 tax year, the deadline is April 15, 2026.
February 2, 2026
Deadline to File Form 945
(If you took an early distribution from your Solo 401k in 2025)
If you withdrew money from your Solo 401k plan in 2025 and withheld federal income tax, you generally must file Form 945 by February 2, 2026.
Early distributions are generally subject to regular income tax plus a 10% additional tax unless an exception applies. Taxable eligible rollover distributions paid to you are generally subject to 20% mandatory withholding.
📝 Exception: If you deposited all required tax payments for 2025 on time, the extended deadline to file Form 945 is February 10, 2025.
March 2, 2026
Deadline to File Form 1099-R (Paper Filing)
(If you moved money out of your Solo 401k in 2025)
If you moved money out of your Solo 401k plan in 2025, you must file Form 1099-R. The deadline for paper filing is March 2, 2026. This generally applies to all withdrawals, rollovers, Roth conversions, Mega Backdoor Roth conversions, RMDs, and Solo 401k loan that went into default and were treated as taxable distributions.
March 31, 2026
Deadline to File Form 1099-R (E-filing)
(Applies if you moved money out of your Solo 401k in 2025)
For those opting for electronic filing, Form 1099-R must be submitted on March 31, 2026. This applies to all withdrawals, rollovers, Roth conversions, Mega Backdoor Roth conversions, RMDs, and failed Solo 401k loan payments.
March 16, 2026
Deadline for Employer & Employee Contributions
(For S corporations, partnerships, and LLCs taxed as S corporations or partnerships)
If your business operates as an S corporation, partnership, or multi-member LLC taxed as an S corp or partnership, you must deposit employer contributions to your Solo 401k by March 16, 2026.
If you previously elected to make employee contributions, those funds must also be deposited by this date.
📝 If you file a tax extension, the deadline extends to September 15, 2026.
April 15, 2026
Deadline for Employer & Employee Contributions
(For C corporations, sole proprietorships, and LLCs taxed as sole proprietorships)
If your business is a C corporation, sole proprietorship, or LLC taxed as a sole proprietorship, you must make employer contributions to your Solo 401k by April 15, 2026.
If you previously elected to make employee contributions, those funds must also be deposited by this date.
📝 If you need more time, filing a tax extension grants you until October 15, 2026 to make these contributions.
Deadline to File Form 8606
(If you contributed to a non-deductible IRA in 2025)
If you contributed to a non-deductible IRA in 2025, you must file Form 8606 to the IRS. This form reports after-tax contributions to an IRA, often part of a Mega Backdoor Roth conversion into a Roth Solo 401k.
You should submit Form 8606 along with your annual tax return by the April 15, 2026 federal tax deadline.
July 31, 2026
Deadline to File Form 5500-EZ
(If you’re closing your Solo 401k or if your account asset value is $250,000 or more)
The deadline to file IRS Form 5500-EZ is seven months after the end of your fiscal year. If your business follows the calendar year, the due date is July 31, 2026.
File Form 5500-EZ if you wish to close your Solo 401k plan, or if your total one-participant plan assets are more than $250,000 at the end of the plan year, which is December 31, 2025 for a calendar-year plan.
📝 Pro Tip: While not required, we generally suggest filing Form 5500-EZ every year, even if you’re not required to. There are edge cases where having a record on file can serve as a safeguard.
September 15, 2026
Extended Contribution Deadline
(For S corporations, partnerships, and LLCs taxed as S corporations or partnerships)
If your business is an S corporation, partnership, or an LLC taxed as an S corporation or partnership, and you filed a tax extension by March 16, 2026, you have until September 15, 2026 to make both employer and employee contributions for the 2025 tax year.
October 15, 2026
Extended Contribution Deadline
(For C corporations, sole proprietorships, and LLCs taxed as sole proprietorships)
C corporations, sole proprietorships, and LLCs taxed as sole proprietorships can make employer and employee contributions until October 15, 2026 if they file an extension by the original due date (typically April 15, 2026 for individual filers).
📝 Important: This article is for informational purposes only and does not constitute tax, legal, or financial advice. Always consult a qualified tax professional or financial advisor before making decisions about your Solo 401k plan.
Frequently Asked Questions
When Is the Deadline to Set Up a Solo 401k?
If you wish to set up a Solo 401k plan for the 2025 tax year, you generally must establish the plan by December 31, 2025. Since the deadline falls during the holiday season, it’s best to complete the setup a few days earlier to avoid any last-minute issues. The same rule typically applies for future years, including 2025 — December 31 is the key deadline to keep in mind.
If you operate as a sole proprietor with no employees, you may be able to adopt the plan after year-end as long as it’s adopted by the filing deadline without extensions. For the 2025 tax year, that deadline is April 15, 2026.
📌 Set up a plan with Carry in a few clicks, or compare the best Solo 401k plan providers here.
When Is the Last Day to Make Solo 401k Contributions?
✅ For S corporations, partnerships, and LLCs taxed as S corporations or partnerships
- Contribution deadline: March 16, 2026
- With an extension: September 15, 2026
✅ For C corporations, sole proprietorships, and LLCs taxed as sole proprietorships
- Contribution deadline: April 15, 2026
With an extension: October 15, 2026
How Much Can I Contribute to My Solo 401k?
For the 2025 tax year, you can contribute up to $70,000 to your Solo 401k across both employee and employer contributions. If you turn 50 or older by year-end, you’re allowed an additional $7,500 in catch-up contributions, bringing your total to $77,500.
What’s the Difference Between Employee and Employer Contributions?
With a Solo 401k plan, you have full control over both your employee and employer contributions. These contributions have different limits and are treated differently for tax purposes.
✅ Employee Contributions (Elective Salary Deferrals)
- Represent a portion of your earnings contributed to your Solo 401k rather than kept in your personal account (even if you don’t receive a formal salary as a self-employed individual).
- You can contribute up to 100% of your compensation, with a maximum of $23,500 ($31,000 if age 50+) for 2025.
- Can be made as pre-tax or Roth contributions.
✅ Employer Contributions (Profit-Sharing)
- Separate from your salary, these are additional contributions made by the business directly into your Solo 401k.
- If your business is incorporated, you can contribute up to 25% of your compensation.
- If your business is not incorporated, you can contribute up to 20% of net earnings.
- Employer contributions can only be made as pre-tax contributions.
The combined employee and employer contributions must not exceed the Solo 401k limit for each tax year. For the 2025 tax year, the maximum total contribution is $70,000 ($77,500 if age 50+).
📌 Also read: Solo 401k Contribution Types Explained
Is There a Deadline to Rollover Funds into a Solo 401k?
There is no deadline to transfer assets from another retirement plan into your Solo 401k.
✅ No Limit on Rollover Amounts — You can rollover any amount from another retirement account without restriction.
✅ Does Not Affect Contribution Limits — Rollovers are separate from annual contribution limits, meaning they won’t count toward your Solo 401k contribution cap for the year.
Do I Need to Be Aware of Any Tax Forms?
Yes! If you have a Solo 401k, here are the key tax forms to know:
- Form 5500-EZ: Required if you’re closing your Solo 401k plan or have $250,000+ in plan assets. However, at Carry, we recommend filing From 5500-EZ every year, regardless of plan assets.
- Form 1099-R: Required whenever funds/assets are moved out of your Solo 401k account, including distributions, rollovers, in-plan conversions, or RMDs.
- Form 945: Required when you take an early distribution from your Solo 401k in order to report the 20% tax withholding.
- Form 8606: Required when you use a non-deductible IRA to rollover to a Roth solo 401k.
📌 Also read: Important Forms for Solo 401k Owners
Disclaimer:
The Carry Learning Center is operated by The Vibes Company Inc. (“Vibes”) and contains generalized educational content about personal finance topics. While Vibes provides educational content and technology services, all investment advisory services discussed on this website are provided exclusively through its wholly-owned subsidiary, Carry Advisors LLC (“Carry Advisors”), an SEC registered investment adviser. The information contained on the Carry Learning Center should not be construed as personalized investment advice and should not be considered as a solicitation to buy or sell any security or engage in a particular investment, accounting, tax or legal strategy. Vibes is not providing tax, legal, accounting, or investment advice. You should consult with qualified tax, legal, accounting, and investment professionals regarding your specific situation.
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