Solo 401k Business Entity Change: Same $72,000 Limit, Different Math
Direct Answer
A Solo 401k business entity change does not require a new plan. When a sole proprietorship becomes an LLC taxed as an S corporation, the new entity becomes the plan sponsor and the existing plan is amended (i.e. restated). The plan name, plan EIN, accounts, and investments stay in place. Contribution limits stay the same, but the calculation shifts from Schedule C income to W-2 wages.
Key Takeaways
- A Solo 401k business entity change does not create a new plan. The existing plan is amended to list the new plan sponsor, such as an LLC taxed as an S corporation.
- The Solo 401k plan name and plan EIN stay the same after an entity change, even when the business obtains a separate business EIN.
- A Solo 401k plan that files Form 5500-EZ, an informational return filed when plan value exceeds $250,000, must list the new entity and its new EIN on later filings.
- A sole proprietor calculates Solo 401k contributions from Schedule C line 31 net income less one-half of self-employment tax, while an S corporation owner uses W-2 wages.
- For 2026, the Solo 401k employee deferral limit is $24,500 and the overall limit is $72,000, plus eligible catch-up contributions.
- A Solo 401k business entity change involves one plan amendment and zero account transfers; brokerage custodians may ask for a copy of the amendment showing the new plan sponsor.
Video: live webinar on Solo 401k business entity change hosted by My Solo 401k Financial.
What happens to my Solo 401k plan if I change my business entity from a sole proprietor to an S corp?
A Solo 401k business entity change leaves the existing plan in place. A business moving from a sole proprietorship to an LLC taxed as an S corporation does not need a new plan. The plan documents are updated to list the new entity as plan sponsor.
A Solo 401k plan can be established without a legal entity. A sole proprietorship can adopt a plan and later graduate to an LLC taxed as an S corporation. The original plan documents list the business as a sole proprietorship, so the documents need an amendment once the LLC taxed as an S corporation operates the business.
“So the answer is no. It’s not a new plan. You really just update the plan documents. It’s a document update.”
“So you’re not shutting down the existing plan and starting a new plan. You’re really just amending, or what they call restating, that existing plan to show that new entity…”
Which entity changes follow the same reasoning?
A Solo 401k business entity change can run in several directions: such as an S corporation becoming a sole proprietorship and an LLC taxed as a sole proprietorship becoming a partnership. Many of the same concepts apply, and the webinar used the sole proprietorship-to-S corporation example to explain them.
What stays the same and what changes in a Solo 401k business entity change?
| Entity | Plan sponsor named in plan documents | Income basis for contributions | Form 5500-EZ sponsor and EIN | Plan name and plan EIN |
|---|---|---|---|---|
| Sole proprietorship (before the change) | The sole proprietorship | Schedule C net income less one-half of self-employment tax | The sole proprietorship and its EIN | As originally established |
| LLC taxed as an S corporation (after the change) | The LLC taxed as an S corporation | W-2 wages | The S corporation and its new business EIN, linked to the prior name and EIN | Unchanged |
In summary, a Solo 401k business entity change replaces the plan sponsor, the contribution income basis, and the Form 5500-EZ sponsor details, while the plan name and plan EIN stay unchanged.
Does a Solo 401k business entity change affect the plan EIN and the business EIN?
A Solo 401k business entity change keeps the plan EIN unchanged, and the plan EIN is separate from the business EIN. A sole proprietor may never have needed a business EIN. The tax advisor may have used a Social Security number instead.
An S corporation needs its own business EIN, which is separate and distinct from the EIN used for the Solo 401k plan. The plan EIN is the number used for Solo 401k accounts and investments. An investment provider, such as a private placement sponsor, asks for the plan EIN.
“So the plan is going to continue. So the name of the plan is going to stay the same. The EIN number of the plan is going to stay the same, but maybe your business EIN changes.”
How does a Solo 401k business entity change affect Form 5500-EZ?
A Solo 401k business entity change affects Form 5500-EZ only when the plan has been filing the form. Form 5500-EZ is an informational tax return filed by the plan sponsor when plan value exceeds $250,000. The sponsor is the business entity, so later filings must show the new entity.
“That 5500-EZ would have listed your sole proprietorship as the plan sponsor, but going forward, it’s going to need to … list your S corporation.”
How does Form 5500-EZ link the prior name and EIN?
Form 5500-EZ includes a section where the filer lists the name and EIN used in the past. Listing the prior name and EIN lets the IRS connect the earlier and later filings.
How does a Solo 401k business entity change affect contribution calculations?
A Solo 401k business entity change does not alter the contribution limits or the contribution types. The plan still offers employee, employer, and voluntary after-tax contributions, including the Mega Backdoor Roth strategy with a Solo 401k plan. The income used to calculate each contribution is what changes.
How does a sole proprietor calculate Solo 401k contributions?
A sole proprietor reports earned self-employment income on Schedule C of Form 1040. The calculation starts with net income on line 31 of Schedule C, less one-half of self-employment tax. An employer contribution can be 20% of that figure.
Employee deferrals can equal 100% of that figure, up to the employee limit. Voluntary after-tax contributions can equal 100% of that figure, up to the overall limit. The three contribution types combined cannot exceed the lesser of that self-employment compensation or the overall limit of $72,000.
How does an S corporation owner calculate Solo 401k contributions?
After the business is taxed as an S corporation, the ability to contribute is based on W-2 wages. This does not mean a person can contribute more. Different numbers determine how much goes into each contribution type, and the totals are aggregated to stay within the applicable limits.
“So it doesn’t impact how much you can contribute in terms of the limits, but it impacts how you determine how much you can contribute. Same plan, different math, in other words.”
Example: A business operates as a sole proprietorship in the first half of a year and as an LLC taxed as an S corporation in the second half. Contributions for the first half are based on Schedule C income. Contributions for the second half are based on W-2 wages. Each period is calculated separately, but one deferral limit and one combined base cap still apply.
What are the 2026 Solo 401k contribution limits?
The 2026 Solo 401k limits do not change with the entity type. The employee limit is $24,500. Tthe catch-up contribution is $8,000, and the super catch-up for ages 60 to 63 replaces it.
“If you’re age 60 to 63 as of the end of 2026, you can make a super catch-up contribution of $11,250 instead of the $8,000. And then your overall limit for 2026 is $72,000 or more if you’re eligible to make those catch-up contributions.”
| Contribution type | 2026 amount or rate | Effect of an entity change |
|---|---|---|
| Employee deferral | $24,500 | Limit unchanged |
| Catch-up contribution (age 50 or older) | $8,000 | Limit unchanged |
| Super catch-up contribution (ages 60 to 63 as of the end of 2026) | $11,250 instead of $8,000 | Limit unchanged |
| Overall limit | $72,000, or more with eligible catch-up contributions | Limit unchanged |
| Employer contribution (sole proprietor) | 20% of Schedule C net income less one-half of self-employment tax | Income basis changes to W-2 wages after the S corporation change |
Do Solo 401k accounts need to move after a Solo 401k business entity change?
A Solo 401k business entity change does not require moving accounts or selling investments. The change replaces only the plan sponsor, so the plan continues with the same name and the same plan EIN. Existing accounts stay in place.
Important: A custodian may need notice of the entity change. Some custodians, such as brokerage firms, match the plan sponsor on their system to the name on the external account that funds contributions. A business that switches from funding contributions from a personal account to an S corporation account may need to tell the brokerage firm and provide a copy of the amendment.
My Solo 401k Financial offers a one-time service for a one-time fee to process the amendment. The amendment is a full restatement of the documents that shows the new business entity. The investments, the account title, and the plan EIN are unaffected.
Solo 401k business entity change: frequently asked questions
Do I need a new Solo 401k plan if I change my business entity?
No. A Solo 401k business entity change does not require a new plan. The existing plan is amended or restated so the new entity, such as an LLC taxed as an S corporation, appears as the plan sponsor. The plan name, plan EIN, accounts, and investments continue, so the business updates documents rather than shutting down and starting over.
Does the Solo 401k plan EIN change when my business entity changes?
No. The Solo 401k plan EIN stays the same after a business entity change, and the plan name stays the same. The business may obtain a new business EIN, which is separate from the plan EIN. The plan EIN remains the number given to investment providers, such as a private placement sponsor.
Do I need to move my Solo 401k accounts or sell investments after changing from a sole proprietorship to an S corporation?
No. Changing from a sole proprietorship to an LLC taxed as an S corporation does not require moving Solo 401k accounts or selling investments. A custodian, such as a brokerage firm, may need notice of the new plan sponsor and a copy of the amendment so the funding account name matches its records.
Does changing to an S corporation change my Solo 401k contribution limits?
No. The 2026 Solo 401k limits stay the same after the entity change. They are a $24,500 employee deferral, an $8,000 catch-up, an $11,250 super catch-up for ages 60 to 63, and a $72,000 overall limit plus eligible catch-ups. The calculation changes, because S corporation contributions are based on W-2 wages instead of Schedule C income.
How are Solo 401k contributions calculated after a business becomes an S corporation?
After a business becomes an S corporation, Solo 401k contributions are calculated from W-2 wages rather than Schedule C net income. A sole proprietor starts from Schedule C line 31 net income less one-half of self-employment tax. When the change happens mid-year, each period is calculated separately, with one deferral limit and one combined base cap.
Do I need to update Form 5500-EZ after a business entity change?
Yes, if the Solo 401k plan has been filing Form 5500-EZ. The plan sponsor files the form when plan value exceeds $250,000. After an entity change, the form must list the new entity and its new business EIN, and the filer can link the prior name and EIN in the designated section.
This article is based on the live webinar hosted by My Solo 401k Financial.
Next step:
Ready to set up or update a plan? Open a Solo 401k account with My Solo 401k Financial. Plan documents are prepared within the same business day after the application is submitted and payment is made.
Educational purposes only: The material above is provided for educational purposes only. Nothing here should be construed as tax, legal, or investment advice, or as a solicitation. Consult a tax attorney and financial professional before making an investment decision.
