What is a 401k Promissory Note?

A 401k promissory note is a topic that comes up frequently — and is just as frequently misunderstood. Is it an investment? Is it a loan? The answer is: it can be both. Understanding the distinction is essential for any Solo 401k plan participant who wants to make the most of their retirement account. This guide breaks down everything you need to know.

Watch: My Solo 401k Financial explains the two types of 401k promissory notes — participant loans and investment notes

What Is a 401k Promissory Note?

At its core, a 401k promissory note is a written loan agreement that documents a loan involving a 401k plan — whether a Solo 401k or a full-time employer 401k. In the context of a Solo 401k, this term most commonly arises in two distinct situations:

A Participant Loan — where the Solo 401k participant (you, as the trustee) borrows money from your own plan
A Promissory Note Investment — where the Solo 401k lends money to a third party as an investment strategy

In both cases, the promissory note is a legally important document that spells out loan terms, repayment schedule, interest rate, parties involved, and consequences if the borrower defaults.

Feature	Participant Loan	Promissory Note Investment
Who borrows?	You (the plan participant)	A third party (investor, business, individual)
Dollar limits?	50% of balance, max $50,000	No IRS dollar limit
Who sets the rules?	IRS statutory regulations	Trustee (you) + plan document
Interest flows to?	Your own Solo 401k	Your Solo 401k (as lender)
Can it involve a disqualified person?	Only you (the participant)	No — prohibited transaction risk

Part 1: The Solo 401k Participant Loan

The Solo 401k participant loan is one of the most powerful and unique features of a Solo 401k plan. Unlike a traditional IRA, a Solo 401k allows you to borrow from your own retirement funds without triggering a taxable distribution — as long as you follow IRS rules.

How Much Can You Borrow?

The IRS sets clear statutory limits on Solo 401k participant loans:

You may borrow up to 50% of your total Solo 401k balance
The maximum loan amount is $50,000
Example: If your Solo 401k has $100,000 or more, you can borrow up to $50,000

💡 Example: Borrowing from Multiple Plans

If you have both a Solo 401k and a full-time employer 401k, you may borrow from both plans — up to the combined limit of $50,000 total. So if each plan has $100,000+, you could potentially borrow $50,000 from each — but only up to the overall $50,000 IRS cap across all plans combined.

Repayment Rules & Schedule

When your Solo 401k plan provider drafts the participant loan documents, the repayment schedule is established at that time. Key repayment rules include:

Loan Feature	Details
Payment frequency	Monthly or quarterly (fixed at time of loan)
Payment type	Fixed principal + interest (not variable)
Interest rate	Prime rate + 1%, or a competitive CD rate + 2%
Standard repayment term	Up to 5 years
Extended term (primary residence)	Up to 15 or 30 years if proceeds fund your primary home purchase
Interest goes to	Your own Solo 401k — not a bank or plan provider

⚠️ Important: Loan Default Rules

Missing a Solo 401k participant loan payment is serious. If a quarterly payment is missed, you have until the end of the following quarter to make it up. If the payment is still not made, the entire outstanding loan balance goes into default and is treated as a taxable distribution — meaning you’ll owe income taxes and potentially a 10% early withdrawal penalty. Always make payments on time.

Part 2: The Solo 401k Promissory Note as an Investment

The second use of a 401k promissory note is entirely different: your Solo 401k becomes the lender, and a third party becomes the borrower. This is classified as an alternative investment — the same category as real estate, precious metals, and cryptocurrency held in a Solo 401k.

ℹ️ Who Can Be the Borrower?

The third-party borrower can be an investor, a construction company, a hard money lender, a business, or an individual friend — but it cannot be you, your spouse, your children, or your parents. These are considered disqualified persons under IRS rules. Lending to a disqualified person would constitute a prohibited transaction.

Secured vs. Unsecured Promissory Notes

When your Solo 401k makes a promissory note investment, you must decide whether the note will be secured or unsecured:

Note Type	Description	Risk Level
Secured Note	Backed by collateral (e.g., real estate, business property). If the borrower defaults, the Solo 401k has recourse to claim that collateral.	Lower risk
Unsecured Note	No collateral. If the borrower defaults, the Solo 401k has no recourse and may lose the investment entirely.	Higher risk

Many Solo 401k trustees prefer secured promissory notes because collateral can significantly reduce risk. If real estate is used as collateral, ensure it is properly documented and legally enforceable.

What Must Be Included in the Promissory Note Investment Document?

As the trustee of your Solo 401k, you are responsible for ensuring the investment benefits the plan. A properly drafted promissory note investment should include all of the following:

Document Element	Details
Lender (Beneficiary)	Your Solo 401k plan name + your name as trustee (e.g., “XYZ Retirement Trust, Jane Doe Trustee”)
Borrower	Individual’s full legal name or correct legal entity name
Loan Amount	Principal amount (and whether interest-only with balloon payment, or principal + interest)
Interest Rate	Based on borrower’s creditworthiness; must comply with state usury laws
Repayment Schedule	Monthly, quarterly, or annual payments with amounts clearly listed
Maturity Date	The date on which the loan must be repaid in full
Collateral	Description of any security or collateral pledged against the loan
Default Terms	What happens if the borrower fails to make payments
Signatures	Both you (as trustee) and the borrower must sign the note

💡 Sample Promissory Note Templates Available

My Solo 401k Financial provides sample promissory note documents in the Forms section of our website. These can serve as a starting point for drafting your own Solo 401k promissory note investment. Always consult a qualified legal professional before finalizing any loan documents.

Who Qualifies for a Solo 401k Plan?

Both the participant loan and the promissory note investment features are exclusive to Solo 401k plans — most full-time employer 401k plans do not allow alternative investments like promissory note investments. To open a Solo 401k, you must meet specific eligibility requirements:

Basic Eligibility Requirements

Requirement	Details
Self-employment income	You must have self-employment or business income
Owner-only business	The business cannot employ full-time W-2 employees working 1,000+ hours (unless they are owners)
Contractors excluded	1099 contractors do not count toward the employee threshold
Under-21 employees excluded	W-2 employees under age 21 can be excluded even if they work 1,000+ hours

Long-Term Part-Time Employee Rule

Even after opening a Solo 401k, you must monitor your ongoing eligibility. Under the Secure Act, the long-term part-time employee rule can affect your plan:

⚠️ Long-Term Part-Time Employee Warning

If a W-2 employee works between 500 and 999 hours for two consecutive years, you will need to close your Solo 401k and transfer assets to a self-directed IRA. Similarly, if a W-2 employee reaches 1,000+ hours in any single year, the plan must be closed.

What Happens to Your Promissory Note If You Must Close the Plan?

If you hold a promissory note investment inside your Solo 401k and circumstances require you to close the plan, the note can be transferred through an in-kind direct rollover:

The promissory note is assigned from the Solo 401k to the self-directed IRA custodian (for the benefit of your IRA)
A Form 1099-R is issued to report the non-taxable direct rollover
A final Form 5500-EZ is filed to formally close the plan with the government

⚠️ Outstanding Participant Loans at Plan Closure

If you have an outstanding Solo 401k participant loan when the plan must be closed, you must pay it off in full. If the loan is not repaid, the remaining balance will be treated as a taxable distribution, subjecting it to income taxes and potentially early withdrawal penalties.

Why Your Solo 401k Plan Document Matters

Not all Solo 401k plans are created equal. Whether a plan allows participant loans or promissory note investments depends entirely on the plan document. The Solo 401k offered by My Solo 401k Financial is specifically designed to support both:

ℹ️ My Solo 401k Financial Plan Features

The Solo 401k plan from My Solo 401k Financial includes both the participant loan feature and the ability to make promissory note investments as alternative investments — alongside real estate, precious metals, cryptocurrency, and more. If you’re using a different plan provider, check your plan document to confirm which features are enabled.

Key Takeaways: 401k Promissory Note at a Glance

Topic	Key Point
Definition	A written loan agreement involving a 401k plan, either as a participant loan or a third-party investment
Participant loan limit	50% of balance, max $50,000; repaid within 5 years (or longer for primary residence)
Interest on participant loan	Goes back to your own Solo 401k — not to a bank
Investment note: who can borrow	Any non-disqualified third party (not you, your spouse, children, or parents)
Investment note: secured vs. unsecured	Secured notes have collateral and lower risk; unsecured notes carry higher risk
Solo 401k eligibility	Must be self-employed with no full-time W-2 employees (1,000+ hours) unless they are owners
Plan closure + note	Promissory note can be transferred via in-kind rollover to a self-directed IRA
My Solo 401k Financial	Offers Solo 401k plans that support both participant loans and promissory note investments

Ready to Use Your Solo 401k for a Promissory Note?

Whether you want to take a Solo 401k participant loan or use your plan to invest in a promissory note, My Solo 401k Financial can help you set up the right plan structure and walk you through every step of the process.

Next Steps:

Open a Solo 401k Account Today | Visit My Solo 401k Financial

Remember: This information is provided for educational purposes only. Always consult with qualified tax, legal, and investment professionals before making decisions involving your retirement funds.