Solo 401(k) vs SEP IRA: Choosing the Best Retirement Plan for Your Business in 2026
When deciding between a Solo 401(k) and a SEP IRA, the key fact to remember is that both retirement accounts share the same total 2026 contribution cap of $72,000. However, the Solo 401(k) offers a unique advantage: you contribute as both the employee and employer, allowing you to save significantly more on the same income. For most solo entrepreneurs without employees, the Solo 401(k) is typically the superior choice. Conversely, a SEP IRA is often the better option if simplicity is your priority, if you have eligible employees, or if you missed the December 31 deadline to set up a Solo 401(k).
To put it simply for founders: a SEP IRA rewards you for earning a lot, while a Solo 401(k) rewards you for being a business of one. If you’re the sole person on payroll, a Solo 401(k) is practically tailor-made for your situation. Yet, many miss out because their bank suggested a SEP IRA first.
If you prefer numbers before opinions, tax attorney Mat Sorensen offers a thorough analysis comparing a $100,000 income across both accounts, illustrating why the Solo 401(k) can nearly double your contributions compared to a SEP IRA.
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 figures here are sourced directly from the IRS, including the $24,500 employee deferral and $8,000 catch-up, as well as the $72,000 total contribution cap and $360,000 compensation limit that apply to both plans in 2026.
Why the Solo 401(k) Lets You Save More on the Same Income
Though both accounts share the same overall contribution limit, many mistakenly believe they function interchangeably. The truth lies in how quickly you can reach that $72,000 ceiling.
A SEP IRA offers a single contribution bucket: the employer contribution. You can contribute up to 25% of your W-2 salary, or approximately 20% of your net self-employment income if you’re a sole proprietor or single-member LLC.
In contrast, a one-participant 401(k) provides two contribution buckets because you act as both employee and employer. As the employee, you can defer up to $24,500 of your earnings. As the employer, you add the same profit-sharing contribution of up to 25%. Combining these two buckets rapidly increases your ability to save.
Here’s an illustrative breakdown for a sole proprietor under age 50 in 2026, based on IRS methodology (net profit minus half self-employment tax, multiplied by roughly 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 the striking difference in the first row: a freelancer earning $40,000 can shelter nearly four times as much using a Solo 401(k). The Solo 401(k) reaches the $72,000 cap at roughly $252,000 in profit, whereas a SEP requires about $377,000. For those aged 50 or older, the Solo 401(k) also offers an $8,000 catch-up contribution, which the SEP IRA does not.
You can calculate your own numbers using the IRS worksheet for self-employed retirement plan contributions, or better yet, consult a CPA. Your precise contribution limits will depend on your business structure, profit, and other retirement plans.
The S-Corp Salary Trap
If your business is taxed as an S corporation, your retirement plan contributions are based solely on your W-2 salary, not your total business profits. This distinction significantly affects your contribution potential.
For example, if you pay yourself a $60,000 salary and take the rest as distributions:
- A SEP IRA allows contributions up to 25% of your salary, or $15,000.
- A Solo 401(k) permits a $24,500 employee deferral plus the $15,000 employer share — totaling $39,500.
To max out at $72,000, a SEP IRA requires a $288,000 salary, while a Solo 401(k) only needs about $190,000. This is why S-corp owners with relatively low salaries often lean toward the Solo 401(k).
Note that deferrals in a Solo 401(k) must be processed through formal payroll, withheld from paychecks, and reported on your W-2 by year-end. Using informal methods, like transferring money and labeling it “salary,” is not acceptable. Proper payroll is essential — retirement plans and the IRS are strict about this.
Additionally, for 2026, if you’re 50 or older and earned more than $150,000 in W-2 wages from your S-corp in 2025, catch-up contributions must be made as Roth contributions. Sole proprietors and partners with only self-employment income are exempt from this requirement, according to the IRS’s catch-up guidance.
When a SEP IRA Is the Smarter Choice
While the Solo 401(k) often takes the spotlight, the SEP IRA remains a valuable tool depending on your circumstances. Consider a SEP IRA if:
- You have eligible employees. Solo 401(k)s only cover you and your spouse. Once you hire qualifying employees, a SEP IRA, SIMPLE IRA, or traditional 401(k) may be required. A SEP IRA requires you to contribute the same percentage of pay for all eligible employees as you do for yourself.
- You earn a high income and want minimal administration. If your profit exceeds $377,000, both plans max out at $72,000 contributions. The SEP IRA’s simpler administration might then be more appealing.
- You missed the December 31 Solo 401(k) setup deadline. SEPs can be established and funded up until your tax filing deadline, including extensions, making it the go-to “I forgot” account.
- Your income fluctuates significantly. SEP contributions are fully discretionary each year. You can skip contributions in lean years and contribute the maximum in prosperous ones.
One important consideration is that SEP IRA balances count in the pro-rata calculation for backdoor Roth IRA conversions, potentially complicating those strategies. Solo 401(k) balances do not. If backdoor Roth contributions are part of your plan, consult a tax professional before loading a large balance into a SEP.
The December 31 Deadline Most Founders Miss
Timing is crucial with retirement accounts, which is why this article is published in November rather than April.
To make employee deferrals for 2026, you must adopt your Solo 401(k) plan by December 31, 2026, and elect your deferrals by that date. This is mandatory for anyone paying themselves W-2 wages through an S corporation and is the safest deadline for sole proprietors as well. After adoption, you generally have until your tax filing deadline to deposit contributions.
There is an exception under SECURE 2.0: sole proprietors or single-member LLCs with no employees can adopt a new Solo 401(k) after year-end and still contribute employee deferrals for the prior year by their tax filing deadline (April 15 for most). However, not all providers support this, so don’t rely on it as your plan.
In contrast, SEP IRAs are more forgiving. According to IRS Publication 560, you can establish and fund a SEP IRA up until your tax return due date, including extensions — potentially as late as September or October 2027 depending on your business entity.
Retirement planning is just one of many year-end decisions. For a full checklist, see 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 not an option. Consider a SEP, SIMPLE IRA, or standard 401(k).
- Find the right income number. Sole proprietors use net profit minus half of self-employment tax. S-corp owners use W-2 salary only.
- Calculate both contributions. For a SEP, it’s about 20% of net self-employment earnings (or 25% of W-2 pay). For a Solo 401(k), add that amount plus up to $24,500 employee deferral, plus catch-up if you’re 50 or older.
- Decide on Roth vs pre-tax. If Roth contributions or loan options matter, the Solo 401(k) is the practical choice.
- Check the calendar. Before December 31: open a Solo 401(k) if it wins out. After December 31: a SEP IRA may be your only 2026 option unless you qualify for the sole-proprietor first-year exception.
- Consult a professional, then open the account. Choose a provider, sign the plan document, set up payroll deferrals if you’re an S corp, and remember to file Form 5500-EZ annually once assets reach $250,000.
Common Mistakes to Avoid With Solo 401(k)s and SEPs
- Defaulting to a SEP IRA. Many accept the SEP because their bank offered it first, potentially leaving $24,500 per year in contribution room unused.
- Using profit instead of W-2 salary as an S-corp owner. Contributions depend on your W-2 wages. Distributions don’t count.
- Double-counting employee deferrals. The $24,500 limit applies per person across all 401(k) plans. If you have another job with a 401(k), your Solo 401(k) deferral limit is reduced accordingly.
- Hiring without checking your plan eligibility. Adding your first eligible employee can disqualify your Solo 401(k). Consult your provider before extending an offer letter.
- Neglecting the Form 5500-EZ filing. Solo 401(k) plans with assets over $250,000 must file annually. Missing this can result in significant penalties.
The Bottom Line
For sole proprietors and solo business owners, the Solo 401(k) is usually the strongest retirement vehicle. It allows higher savings on less income, offers catch-up contributions, includes a genuine Roth option, and permits loans in emergencies. The SEP IRA earns its place when you have employees, when your earnings are high enough for both plans to max out, or when timing forces your hand.
Your business already pays you — make sure it pays your future self too by selecting the right account before December 31 chooses for you.
This article is educational and does not constitute personal tax, legal, or financial advice. Contribution limits, entity type, and individual circumstances vary. Consult a CPA, enrolled agent, or fiduciary financial adviser before opening or funding any 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 with no employees, a Solo 401(k) is better. It allows a $24,500 employee deferral on top of the employer contribution, 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 in 2026. The Solo 401(k) adds an $8,000 catch-up for those 50 or older, or $11,250 for ages 60 to 63. SEP IRAs offer no catch-up contribution.
When is the deadline to open a Solo 401(k) for 2026?
Generally, the plan must be adopted by December 31, 2026, to make employee deferrals for that year. 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, but contributions from the same business share a single $72,000 limit. You cannot use the IRS model SEP form if you maintain another retirement plan. Most solo founders choose one. Always check with your provider and tax professional first.
Does a SEP IRA allow Roth contributions?
Since SECURE 2.0, Roth SEP contributions are allowed, but few custodians offer this feature yet. SEPs do not allow employee deferrals. If Roth savings are important, a Solo 401(k) with a Roth option is generally the better choice.
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