Solo 401(k) vs SEP IRA: Choosing the Right Retirement Plan for Your Business in 2026
When deciding between a Solo 401(k) and a SEP IRA for retirement savings in 2026, the key fact is that both accounts share the same total contribution cap of $72,000. However, the Solo 401(k) offers a distinct advantage by allowing contributions as both the employee and the employer, enabling you to save significantly more on the same income. For most solo entrepreneurs and single-owner businesses without employees, the Solo 401(k) is usually the superior choice. Meanwhile, a SEP IRA shines in situations where simplicity is paramount, when you have eligible employees, or if you missed the December 31st deadline for setting up a Solo 401(k).
To put it simply: a SEP IRA rewards you for earning a lot, while a Solo 401(k) rewards you for being a business of one. If you are the sole person on payroll, a Solo 401(k) is tailored almost perfectly to your needs. Yet, many business owners never open this account because their bank or provider initially offered them a SEP IRA.
If you prefer to see the numbers before diving into explanations, tax attorney Mat Sorensen provides a detailed breakdown comparing contributions on a $100,000 income for both accounts, illustrating why the Solo 401(k) nearly doubles the SEP IRA in potential savings.
Solo 401(k) vs SEP IRA: Side-by-Side Comparison for 2026
| Solo 401(k) | SEP IRA | |
|---|---|---|
| Who it’s for | Business owners with no employees other than a spouse | Any size business, including self-employed people with employees |
| Employee deferral | Up to $24,500 in 2026 | None (only grandfathered SARSEPs allow deferrals) |
| Employer contribution | Up to 25% of W-2 pay (about 20% of net self-employment earnings for sole proprietors) | Same: up to 25% of pay (about 20% of net self-employment earnings) |
| Total 2026 cap | $72,000, plus catch-up | $72,000 |
| Catch-up (age 50+) | $8,000; $11,250 for ages 60 to 63 | None |
| Roth option | Roth deferrals widely available | Allowed by law since SECURE 2.0, but few custodians offer it |
| Loans | Allowed if the plan permits (the lesser of $50,000 or half your vested balance) | Not allowed |
| Setup deadline | Generally December 31 to make that year’s employee deferrals | Your business tax return due date, including extensions |
| Paperwork | Plan document; Form 5500-EZ once assets reach $250,000 | Form 5305-SEP or a prototype; no annual IRS filing |
| Best for | Solo founders who want to save the most, especially at $40k to $250k of profit or with a low S-corp salary | Owners with employees, or anyone who wants the simplest possible setup |
All 2026 numbers come directly from the IRS: the employee deferral limit of $24,500, the total contribution cap of $72,000, and the $360,000 compensation limit that applies to both plans.
Why the Solo 401(k) Lets You Save More on the Same Income
Although both accounts share the same maximum contribution limit, they differ significantly in how quickly you can reach that limit.
A SEP IRA has only one contribution bucket: the employer contribution. You can contribute up to 25% of your W-2 salary, or roughly 20% of your net self-employment earnings if you operate as a sole proprietor or single-member LLC. That’s the full extent of your contributions.
In contrast, a Solo 401(k) provides two contribution buckets because you act as both the employee and employer. As the employee, you can defer up to $24,500 of your income. On top of this, as the employer, you can contribute the same 25% employer share allowed by the SEP IRA. Combining these buckets results in a much faster path to the $72,000 limit.
Here’s a look at approximate maximum contributions for a sole proprietor under age 50 in 2026, based on IRS calculations (net profit minus half self-employment tax, times about 20%):
| Net business profit | Max SEP IRA contribution | Max Solo 401(k) contribution | Extra with Solo 401(k) |
|---|---|---|---|
| $40,000 | ~$7,400 | ~$31,900 | ~$24,500 |
| $60,000 | ~$11,150 | ~$35,650 | ~$24,500 |
| $100,000 | ~$18,600 | ~$43,100 | ~$24,500 |
| $150,000 | ~$27,900 | ~$52,400 | ~$24,500 |
| $250,000 | ~$47,000 | ~$71,500 | ~$24,500 |
| About $377,000 | $72,000 | $72,000 | $0 (both maxed) |
Notice in the first example that a freelancer earning $40,000 can shelter nearly four times as much in a Solo 401(k) compared to a SEP IRA. The Solo 401(k) reaches the $72,000 limit at roughly $252,000 of profit, while a SEP needs about $377,000 to hit the cap. If you are age 50 or older, the Solo 401(k) offers an $8,000 catch-up contribution on top of these amounts, whereas the SEP IRA does not.
For precise calculations tailored to your situation, use the IRS worksheet for calculating your own retirement plan contribution, or consult a CPA. Your contribution limit will depend on your profit, business entity, and other retirement plans.
The S-Corp Salary Trap
If your business is taxed as an S corporation, your retirement contributions are based solely on your W-2 salary, not your total business profit. This distinction can drastically change contribution limits.
For example, if you pay yourself a $60,000 salary and take the rest of your earnings as distributions, a SEP IRA allows contributions up to 25% of that salary, or $15,000. A Solo 401(k) permits the $24,500 employee deferral plus the same $15,000 employer contribution, totaling $39,500. To max out at $72,000 contributions, a SEP would require a $288,000 salary, whereas a Solo 401(k) would need about $190,000.
This is why many low-salary S-corp owners favor the Solo 401(k). Keep in mind, deferrals must be processed through payroll, withheld from paychecks by year-end, and reported on your W-2. If you are still paying yourself informally (for example, via transfers without payroll), it’s critical to formalize your payroll system. Retirement plans and the IRS both expect accurate payroll records.
Another important note for 2026: if you are 50 or older and earned more than $150,000 in W-2 wages from your company in 2025, catch-up contributions must now be made as Roth contributions. Sole proprietors and partners with only self-employment income are exempt from this rule, according to the IRS’s catch-up contribution guidance.
When a SEP IRA Is the Smarter Choice
The SEP IRA remains a strong option in the right circumstances. Consider a SEP if:
- You have eligible employees. A Solo 401(k) only covers you and your spouse. Hiring qualifying employees means you must choose a different plan. A SEP IRA can cover employees but requires you to contribute the same percentage of pay for all eligible employees as you contribute for yourself.
- You earn very high profits and want minimal administration. If your profits exceed $377,000, both plans max out at $72,000, making the SEP’s simplicity more attractive.
- You missed the December 31 deadline for Solo 401(k) setup. A SEP IRA can be established and funded up to your tax filing deadline, including extensions, offering a “last-minute” retirement savings option.
- Your income fluctuates significantly. SEP contributions are discretionary; you can skip contributions in lean years and maximize them in good years.
One subtle factor to consider: SEP IRA balances count in the pro-rata rule if you perform a backdoor Roth IRA conversion, potentially complicating tax planning. Solo 401(k) balances do not affect this calculation. If backdoor Roth contributions are part of your strategy, consult your tax advisor before accumulating a large SEP balance.
The December 31 Deadline Most Founders Miss
Timing matters. To make employee deferrals for 2026 in a Solo 401(k), you generally must establish the plan by December 31, 2026 and elect your deferral by that date. This applies especially to those paying themselves W-2 wages through an S corporation. Once the plan exists, you typically have until your tax filing deadline to deposit the deferrals.
An exception under SECURE 2.0 allows sole proprietors and single-member LLCs with no employees to adopt a new Solo 401(k) after year-end and still make employee deferrals for 2026, provided contributions are made by the tax filing deadline without extensions (usually April 15). However, not all plan providers support this, so don’t rely on it.
On the other hand, a SEP IRA is more lenient. According to IRS Publication 560, you can establish and fund a SEP up to your business tax return due date, including extensions. With an extension, this can push 2026 SEP contributions as late as September or October 2027, depending on your business entity.
Retirement planning is just one of many year-end decisions. For more guidance on other important moves before December 31, check out the year-end tax moves every one-person business should make before December 31.
How to Choose Between a Solo 401(k) and a SEP IRA: 6 Practical Steps
- Confirm who’s on your team. If anyone other than you and your spouse works enough hours to be eligible, a Solo 401(k) is no longer an option. Consider a SEP, SIMPLE IRA, or traditional 401(k).
- Identify the correct income figure. Sole proprietors use net profit minus half of self-employment tax. S-corp owners use only W-2 salary.
- Calculate potential contributions for both plans. SEP: approximately 20% of net self-employment earnings (or 25% of W-2 pay). Solo 401(k): that same amount plus up to $24,500 employee deferral, plus catch-up contributions if applicable.
- Decide between Roth and pre-tax contributions. If you want Roth savings or loan access, the Solo 401(k) is usually the better fit.
- Check the calendar. Before December 31: set up a Solo 401(k) if it’s your best option. After December 31: a SEP may be your only choice for 2026 unless you qualify for the sole proprietor’s first-year exception.
- Consult a professional and open your account. Choose a reputable provider, sign the plan document, set up deferrals through payroll if you’re an S-corp, and track Form 5500-EZ filing requirements once assets reach $250,000.
Common Mistakes to Avoid With Solo 401(k)s and SEPs
- Defaulting to a SEP IRA. Sometimes banks offer SEP IRAs first, leading owners to miss out on $24,500 of potential additional contributions.
- Using profit instead of W-2 salary as an S-corp owner. Retirement contributions must be based on actual salary, not distributions or total profit.
- Doubling up on deferrals. The $24,500 employee deferral limit applies across all 401(k) plans combined. If you have a W-2 job with a 401(k), your Solo 401(k) deferrals count toward that limit.
- Hiring employees without updating your plan. Adding an employee may disqualify your Solo 401(k). Consult your plan provider before hiring.
- Forgetting Form 5500-EZ filing. Once your Solo 401(k) assets exceed $250,000, annual IRS filing is mandatory. Missing this can lead to significant penalties.
The Bottom Line
For solo business owners, a Solo 401(k) typically offers the most powerful retirement savings vehicle. It enables higher contributions on less income, includes catch-up options, provides a genuine Roth feature, and even allows loans in emergencies. A SEP IRA is a solid alternative when you have employees, your profits are high enough that both plans max out, or you missed the Solo 401(k) setup deadline.
Your business already pays you. Make sure it pays your future self too by choosing your retirement plan before December 31 chooses for you.
This article is educational and not personalized tax, legal, or financial advice. Contribution limits, entity types, and individual circumstances vary. Always consult a CPA, enrolled agent, or fiduciary financial advisor before opening or funding a retirement plan.
Solo 401(k) vs SEP IRA FAQs
Which is better for a one-person business, a Solo 401(k) or a SEP IRA?
For most solo owners without employees, the Solo 401(k) is preferable. It allows a $24,500 employee deferral on top of the employer contribution a SEP offers, plus catch-up contributions, Roth deferrals, and loan options. A SEP IRA is simpler and better suited for businesses with employees.
What are the 2026 contribution limits for a Solo 401(k) and SEP IRA?
Both plans cap total contributions at $72,000 for 2026. A Solo 401(k) allows an $8,000 catch-up contribution for those age 50 or older (or $11,250 for ages 60 to 63). SEP IRAs do not have catch-up contributions.
When is the deadline to open a Solo 401(k) for 2026?
The general deadline to make 2026 employee deferrals is December 31, 2026. Sole proprietors with no employees opening their first plan may adopt it by their tax filing deadline without extensions. SEP IRAs can be opened until the tax return due date, including extensions.
Can I have both a Solo 401(k) and a SEP IRA?
Sometimes yes, but contributions from the same business share the $72,000 total limit. Additionally, if you maintain another retirement plan, you cannot use the IRS model SEP form. Most solo founders choose one plan. Check with your provider and tax advisor before proceeding.
Does a SEP IRA allow Roth contributions?
SECURE 2.0 permits Roth SEP contributions, but many custodians do not yet offer this option. SEP IRAs also do not allow employee deferrals. If Roth savings are important to you, a Solo 401(k) with a Roth feature is generally the better choice.
