Setting Up a Solo 401(k): A Step-by-Step Guide for Freelancers

More freelancers know about the Solo 401(k) than actually have one. The tax advantages are well understood at this point: shelter up to $72,000 of income per year, reduce your taxable income dollar-for-dollar, and let those dollars compound tax-deferred for decades. What trips people up is the setup. There is a vague sense that it involves paperwork, plan documents, and financial institutions, and at some point that vague sense becomes a reason to put it off until next year.

The reality is that opening a Solo 401(k) at a major brokerage takes about 20 minutes of active effort and another week of waiting for account approval. The hardest part is knowing which steps happen in which order. This guide walks through exactly that.

Who Can Open a Solo 401(k)?

You qualify for a Solo 401(k) if you have self-employment income and no full-time employees other than a spouse. That covers a wide range of situations: sole proprietors, single-member LLCs, freelancers, independent contractors, gig workers, and side-hustlers who also have a W-2 job from an employer. The W-2 job doesn't disqualify you. What matters is that you have some net income from self-employment and aren't running a business with employees on payroll.

One common edge case: if you have a part-time employee who works fewer than 1,000 hours per year, you may still qualify. The exact threshold depends on the plan documents, so if you have any employees at all, confirm with the brokerage before applying.

A spouse who also works in your business can participate in the same Solo 401(k), which effectively doubles the household contribution limit.

The Six Steps to Open Your Account

1. 1
   Confirm your net self-employment income for the year

   Your employer contribution limit is calculated from your net SE earnings, which is net profit minus half of your SE tax. Before you can decide how much to contribute, you need a reasonable estimate of what you will earn this year. You don't need exact figures yet, but you do need a ballpark to avoid over-contributing. A quick estimate: take your expected gross revenue and subtract your expected deductible business expenses to get net profit. Multiply by 0.9235 for the SE base, multiply that by 15.3% for SE tax, and subtract half the SE tax from net profit. Your maximum employer contribution is 20% of the result (the self-employed equivalent of a 25% plan rate), capped so the total stays under $72,000.

2. 2
   Choose a brokerage

   Pick where you want the account held. The main considerations are whether the plan allows Roth contributions, what investment options are available, and whether there are any account fees. See the brokerage breakdown below. For most freelancers with no strong existing relationship with any particular institution, Fidelity is a reasonable starting point.

3. 3
   Complete the application and plan adoption agreement

   This is where most people expect complexity and find surprisingly little. Major brokerages have moved their Solo 401(k) applications almost entirely online. You will enter your name, address, Social Security number or EIN, business name, business structure (sole proprietor, LLC, etc.), and basic income information. You will also select whether you want a Roth option and whether you want loan provisions included in the plan. Most people leave loan provisions off unless they expect to need them. The application generates a plan document package that is the legal basis of your 401(k).

4. 4
   Sign and return the plan adoption documents

   After completing the online application, you will receive a plan adoption agreement to sign. This is the document that legally establishes the plan. At Fidelity and Schwab, this can be done with an electronic signature. Some brokerages still require a wet signature and mailing the form back. Read the instructions carefully. The date you sign the adoption agreement is typically treated as the plan establishment date for IRS purposes, which is why you should aim to finish this step before December 31.

5. 5
   Fund the account with your first contribution

   Once the account is approved and open (usually within a few business days to two weeks depending on the brokerage), you can transfer funds in. You have two contribution types to decide on: the employee elective deferral ($24,500 max for 2026, or $32,500 if you're 50 or older) and the employer profit-sharing contribution (about 20% of net SE earnings). You must elect the employee deferral by December 31, but IRS Publication 560 lets a self-employed owner deposit it as late as the tax filing deadline, including extensions, and the employer contribution has the same deadline. Check your plan document, since some providers set earlier deposit rules. Many people make a lump-sum contribution once they have finalized their year-end numbers, rather than contributing throughout the year.

6. 6
   Choose your investments

   Money sitting in a 401(k) account earns nothing until you actually invest it. This step trips up a surprising number of people who open the account and then forget to select funds. At minimum, pick a target-date fund matching your expected retirement year (for example, a 2055 fund if you're in your early 30s) if you don't want to think about asset allocation. If you want more control, low-cost index funds tracking the total U.S. stock market, international stocks, and bonds are the standard building blocks. The exact investment decision is beyond the scope of this article. The one thing to do is avoid leaving the money uninvested in a money market default.

Where to Open Your Solo 401(k): Brokerage Options

A few years ago, the standard advice was to compare Fidelity, Vanguard, and Schwab. That comparison has changed. In 2023, Vanguard discontinued new Individual 401(k) applications and directed existing customers to Ascensus, a third-party retirement plan administrator. If you already have a Vanguard Solo 401(k), it likely transferred to Ascensus. If you are opening a new one, Vanguard is not an option. Here is where things actually stand for new accounts in 2026:

The Deadlines That Matter

The deadline structure for a Solo 401(k) is one of the most commonly misunderstood aspects of the account. Employee and employer contributions follow different rules (the employee deferral has to be elected by year-end), and the plan establishment deadline is separate from both.

December 31 used to be a hard deadline for the plan. Two changes softened it. The SECURE Act of 2019 lets an employer adopt a plan after year-end, up to the filing deadline, and still make employer (profit-sharing) contributions for the prior year. SECURE 2.0 went further for sole proprietors: since 2023, IRS Publication 560 says a sole proprietor with no employees can adopt a new 401(k) after year-end, as long as it is adopted by the tax filing deadline without extensions, and first-year employee deferrals count for the prior year if they are paid in by that same date. For 2026, that means adopting the plan and depositing the deferrals by April 15, 2027. The exception only covers a new plan's first year, an extension does not stretch it, and not every brokerage handles these late adoptions, so December 31 is still the date to aim for.

A practical note: if you are reading this in the fall and haven't opened your account yet, do not wait until late December. Brokerage processing times can run one to two weeks, and some institutions have internal holiday cutoff dates for new account approvals. An application submitted on December 28 may not be approved in time. October or November is a much safer target.

What Happens If You Miss December 31?

If December 31 passes and you don't have a plan established, you have two routes. If you are a sole proprietor with no employees and have never had this plan, you can still adopt a new Solo 401(k) for the prior year by April 15 (see above), provided your brokerage will process it. Otherwise, a SEP-IRA is the main alternative: you can open and fund a SEP-IRA all the way up to your tax filing deadline (including extensions), which gives you until April 15 or even October 15 to act. The trade-off is that SEP-IRA contributions are employer-only, capped at the same 20% of net SE earnings as the Solo 401(k)'s employer bucket, and a SEP-IRA does not accept Roth employee deferrals.

For a freelancer earning $60,000 in net SE income, the SEP-IRA limit would be roughly $11,150 (20% of $55,761, which is net profit minus half the SE tax). A Solo 401(k) with the same income could shelter about $35,650, combining the $24,500 employee deferral with the same employer contribution. The difference is meaningful, especially for someone earlier in their career trying to accumulate savings quickly.

In short: if you miss December 31, ask your brokerage about a late first-year adoption before April 15, use a SEP-IRA as the fallback if that is not possible, and open the Solo 401(k) in January either way so it is in place for the next tax year.

After You Open the Account: Staying on Track

Once the account is open, the ongoing maintenance is light. Keep up with these four things.

Designate a beneficiary. Most brokerages prompt you to do this during setup, but confirm it is on file. A retirement account without a named beneficiary can create complications for your estate.

Keep contribution records. Track the date and amount of each contribution, and whether it was classified as an employee deferral or employer profit-sharing. This distinction matters when you file Schedule 1 and Form 8880 (if applicable), and it matters if you are ever audited.

Watch the Form 5500-EZ threshold. Once your Solo 401(k) plan assets exceed $250,000 at the end of any plan year, you are required to file Form 5500-EZ annually. It is not a complicated form, but the penalty for forgetting to file it is steep: $250 per day, up to $150,000. Set a calendar reminder to check your account balance in early January each year.

Reassess contributions annually. Your net SE income varies year to year, which means your maximum employer contribution changes. Run the calculation each fall using your best income estimate for the year, then top up before the deadlines. If you have been deferring from each payment throughout the year, do a final reconciliation in November or December to make sure you haven't over- or under-contributed.