Completing a solo 401k plan document template comes down to two things: gathering the right business and personal data before you start, and making informed elections in the adoption agreement where the real decisions live. Most owners use a pre-approved template from a financial institution or third-party provider, sign it electronically, and keep it on file rather than sending it to the IRS. SECURE 2.0 also changed the adoption deadline, so a sole proprietor who missed December 31 can still set up a plan for the prior tax year.
Gather This Before You Open the Template
The template will ask for the legal name of your business and its Employer Identification Number so contributions and tax filings tie to the correct entity. You’ll also set a plan year; most owners align it with the calendar year ending December 31 to keep accounting clean.1Internal Revenue Service. One-Participant 401k Plans
Your business structure drives how contributions get calculated, and the template needs to reflect that. If you’re a sole proprietor, single-member LLC taxed as a sole proprietorship, or a partner, “earned income” means your net self-employment earnings minus half of your self-employment tax minus your own plan contributions. IRS Publication 560 has the rate tables and worksheets for that calculation. If your business is an S-corp or C-corp, contributions are based on the W-2 wages the corporation pays you, which is a simpler number to work with.1Internal Revenue Service. One-Participant 401k Plans
Decide upfront whether your spouse will participate. If your spouse earns income from the business, they can be a second plan member, which effectively doubles the household contribution capacity. The plan can only cover you (and a spouse); the business must have no other employees.
One practical detail: the plan trust may need its own EIN if you want to open a bank or brokerage account in the trust’s name. The IRS doesn’t require a separate EIN for a one-participant plan, but many financial institutions do. You can get one for free on the IRS website in a few minutes.
How a Pre-Approved Template Is Built
A pre-approved plan document has already received a favorable opinion letter from the IRS confirming the language meets qualification requirements. Under Revenue Procedure 2017-41, the IRS combined its former master-and-prototype and volume-submitter programs into a single Opinion Letter program that sets the standards providers must follow.2Internal Revenue Service. Revenue Procedure 2017-41 Using a pre-approved template means you inherit that compliance rather than building it from scratch.
The document typically comes in two parts. The basic plan document holds the boilerplate legal language and generally isn’t customized. The adoption agreement is where you make elections by checking boxes and filling in blanks: contribution types, compensation definition, eligibility, loans, distributions.3Internal Revenue Service. 2017 Pre-Approved Retirement Plan Opinion Letter Program Read the adoption agreement carefully. This is the part that governs how your plan actually runs.
The Elections That Actually Matter
Eligibility
Even though you’re the only participant, the plan document needs eligibility rules. Most solo 401k owners choose immediate eligibility with no age or service requirements, which is the simplest setup and fine for a one-person plan.1Internal Revenue Service. One-Participant 401k Plans
Compensation Definition
This determines the dollar base for your employer contribution percentage, and picking the wrong one causes over- or under-contributions. For a corporation, compensation is generally the W-2 wages the business pays you. For a sole proprietor, the plan should reference the earned-income formula. Templates usually offer several definitions; match the one to your business structure.
Profit-Sharing Cap
The adoption agreement asks the maximum profit-sharing percentage you want to allow, up to 25 percent of compensation for W-2 earners.1Internal Revenue Service. One-Participant 401k Plans Most owners elect the maximum. You’re never required to contribute the full amount in any given year, but capping it low in the document locks you out of larger contributions later unless you amend the plan.
Roth Option
One of the most consequential checkboxes is whether to include a designated Roth contribution program under Section 402A. Pre-tax deferrals reduce your taxable income now but are taxed on withdrawal; Roth deferrals use after-tax dollars and grow tax-free.4Office of the Law Revision Counsel. 26 USC 402A – Optional Treatment of Elective Deferrals as Roth Contributions If the plan document doesn’t include the Roth option, you can’t make Roth deferrals at all, and adding it later requires a plan amendment. There’s no cost to including it upfront, so most advisors recommend checking that box even if you don’t plan to use it right away.
SECURE 2.0 adds a further reason. For tax years beginning after December 31, 2026, certain high earners (those with FICA-taxable wages of $145,000 or more, indexed for inflation) will be required to make all catch-up contributions as Roth. Building the Roth option into the document now prepares the plan for that rule.
Loan Provisions
A solo 401k can allow you to borrow from your own account, but only if the plan document explicitly includes loan provisions. This is another checkbox that’s easy to overlook and impossible to use retroactively without a plan amendment. If there’s any chance you’ll want access to funds before retirement, include the loan option at setup.
The mechanics of any loan are set by Section 72(p): the maximum is the lesser of 50 percent of your vested balance or $50,000, with a $10,000 floor if half your balance is less than that.5Internal Revenue Service. Retirement Topics – Loans The $50,000 cap is reduced by your highest outstanding loan balance during the prior 12 months.6Internal Revenue Service. Retirement Plans FAQs Regarding Loans Repayment runs five years with substantially equal payments at least quarterly, and a loan that fails those rules is treated as a taxable distribution.
Contribution Limits (For Context)
The document sets the framework; the IRS sets the annual dollar ceilings separately. For 2026, total contributions can reach $72,000, or $80,000 with the age-50 catch-up, with an enhanced catch-up bringing ages 60 through 63 up to $83,250.7Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,5008Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions Your elections in the document don’t need to match these numbers; they need to allow you to reach them.
Deadlines and Signing the Document
This is where the law changed and where older guidance can mislead you. Before SECURE 2.0, you had to establish a solo 401k by December 31 to make elective deferrals for that tax year. For 2023 and later tax years, a sole proprietor with no employees can adopt a solo 401k after year-end, as long as the plan is adopted by the tax filing deadline (not including extensions). For most calendar-year sole proprietors, that’s April 15 of the following year. The new rule also permits retroactive elective deferrals for the prior year.9Internal Revenue Service. Publication 560 – Retirement Plans for Small Business Employer profit-sharing contributions have long had a more generous window and can be made up to the tax filing deadline including extensions.
Signing is straightforward. The employer (you) and the trustee (typically also you) both sign the adoption agreement. Revenue Procedure 2017-41 specifically permits electronic signatures for adopting a pre-approved plan, so no notary or wet ink is required.2Internal Revenue Service. Revenue Procedure 2017-41 The signature date establishes when the plan became operational for tax purposes, which matters if you’re relying on the SECURE 2.0 retroactive-deferral rule.
After You Sign
You don’t file the plan documents with the IRS at setup, but you do need to keep them permanently. If the plan is ever audited, you’ll need every version of the plan document, every signed adoption agreement, and every amendment. The IRS has been known to request records going back a decade or more during plan termination reviews, so the safe rule is to never discard signed plan documents.
Pre-approved plan providers periodically issue restatements to incorporate changes in federal law. When yours does, review the updated document and sign a new adoption agreement within the window the provider specifies. Failing to adopt required amendments means the plan no longer complies and loses its tax-qualified status.10Internal Revenue Service. 401(k) Plan Fix-It Guide – You Haven’t Updated Your Plan Document Within the Past Few Years to Reflect Recent Law Changes The IRS cycles pre-approved plan restatements roughly every six years, so this isn’t constant work, but missing one is a serious problem.
One boundary worth noting: completing the template is separate from the plan’s annual reporting. Once total assets across all your one-participant plans exceed $250,000 at the end of a plan year, you must file Form 5500-EZ.11Internal Revenue Service. Instructions for Form 5500-EZ Nothing in the plan document controls that threshold, but the obligation attaches to any plan you adopt.