Solo 401(k) vs SEP IRA: Choosing the Right Retirement Plan for 2026
When deciding between a Solo 401(k) and a SEP IRA for your retirement savings in 2026, it essentially boils down to one key factor: both accounts impose a total contribution limit of $72,000, yet a Solo 401(k) offers you the unique advantage of contributing both as an employee and employer. This dual contribution capability means you can stash away significantly more retirement funds on the same income compared to a SEP IRA. For most solo entrepreneurs without employees, the Solo 401(k) typically emerges as the superior choice. Conversely, a SEP IRA shines when simplicity is paramount, if you have eligible employees, or if you missed the December 31 deadline to establish a Solo 401(k) for that tax year.
To put it succinctly, a SEP IRA rewards high earnings, while a Solo 401(k) rewards the business of one. Many founders miss out on the Solo 401(k) simply because their financial institution initially offers the SEP IRA instead. For those who prefer to see the numbers first, tax attorney Mat Sorensen’s analysis of a $100,000 income illustrates how the Solo 401(k) can nearly double the savings potential compared to the 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 2026 figures are sourced from the IRS: the employee deferral limit of $24,500 and the $8,000 catch-up, alongside the overall $72,000 contribution cap and $360,000 compensation limit applicable to both plans.
Why the Solo 401(k) Lets You Save More on the Same Income
Despite sharing the same overall contribution ceiling, the Solo 401(k) and SEP IRA differ significantly in how quickly you can reach that limit. A SEP IRA offers a single contribution bucket—employer contributions—allowing you to contribute up to 25% of W-2 wages (or roughly 20% of net self-employment earnings for sole proprietors). In contrast, a Solo 401(k) provides two contribution buckets: as the employee, you can defer up to $24,500 of your income, and as the employer, you can add the same 25% profit-sharing contribution. Combined, this dual-contribution strategy substantially increases your savings potential.
For example, consider a sole proprietor’s 2026 contributions based on IRS calculations (net profit minus half self-employment tax, multiplied by roughly 20%, under age 50):
| 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) |
From the table, a freelancer earning $40,000 can shelter roughly four times more with a Solo 401(k). The Solo 401(k) hits the $72,000 limit at around $252,000 in profit, whereas the SEP requires about $377,000 to max out. Additionally, if you’re 50 or older, a Solo 401(k) offers an $8,000 catch-up contribution, which a SEP IRA does not provide.
It’s wise to calculate your own numbers using the IRS worksheet for self-employed retirement plan contributions or consult a CPA, as your contribution limits can vary based on business structure, other retirement plans, and income.
The S-Corp Salary Trap
If your business is taxed as an S corporation, your retirement contributions hinge on your W-2 salary rather than your overall business profit. This distinction significantly alters the savings potential.
For instance, if you pay yourself a $60,000 salary and take the remainder as distributions, a SEP IRA allows contributions up to 25% of that salary—$15,000. Meanwhile, a Solo 401(k) permits employee deferrals of $24,500 plus the same $15,000 employer contribution, totaling $39,500. To reach the $72,000 cap, a SEP IRA needs a $288,000 salary, while a Solo 401(k) requires about $190,000.
This scenario explains why many low-salary S-corp owners gravitate toward the Solo 401(k). Note that employee deferrals must be processed through payroll, withheld from paychecks by year-end, and reported on your W-2. If you’re still paying yourself informally (e.g., via transfers labeled as salary), it’s crucial to formalize payroll first. As one founder learned the hard way, sloppy payroll practices won’t be overlooked by the IRS or retirement plan administrators.
Another important 2026 update: if you’re 50 or older and earned over $150,000 in W-2 wages in 2025, your catch-up contributions must be made as Roth contributions. In contrast, sole proprietors and partners with self-employment income aren’t subject to this Roth-only catch-up rule, as clarified by the IRS’s catch-up contribution guidance.
When a SEP IRA Is the Smarter Choice
The SEP IRA remains a valuable retirement tool when used appropriately. Consider a SEP IRA if:
- You have eligible employees. Solo 401(k)s only cover you and your spouse. Hiring qualifying employees means you must switch to a different plan. A SEP IRA allows employee coverage but requires contributions at the same percentage of pay for all eligible employees as for yourself.
- You earn well above $377,000. At very high profits, both accounts max out at $72,000. The SEP’s simplicity then becomes more attractive.
- You missed the December 31 deadline for Solo 401(k) setup. You can still open and fund a SEP IRA up to your tax filing deadline, including extensions—making it the go-to “oops” account.
- Your income fluctuates significantly. SEP contributions are fully discretionary. You can skip contributions in a lean year and max out when profits surge.
One subtle factor often overlooked: SEP IRA account balances count in the pro-rata calculation for backdoor Roth IRA conversions, potentially complicating that strategy. Solo 401(k) balances do not count in this calculation. If backdoor Roth contributions are part of your financial plan, consult your tax advisor before funding a large SEP balance.
The December 31 Deadline Most Founders Miss
Many founders miss the critical deadline for Solo 401(k) setup, which is why this topic is addressed in November rather than April. To make 2026 employee deferrals, you generally must have your Solo 401(k) plan adopted by December 31, 2026, and your deferral election made by that date. This deadline applies especially to those paying themselves W-2 wages through an S corporation, and it’s the safest approach for all.
Once the plan is adopted, you usually have until your tax return due date to deposit the contributions. There is a rare exception under SECURE 2.0: sole proprietors or single-member LLCs with no employees may adopt a new Solo 401(k) after the year ends and still make employee deferrals for the prior year, provided the contributions are made by the tax filing deadline without extensions (typically April 15). However, not all providers support this, so don’t rely on it as your primary planning strategy.
In contrast, SEP IRAs offer more flexibility. IRS Publication 560 states you can establish and fund a SEP up to your business tax filing deadline, including extensions. With extensions, SEP contributions for 2026 may be made as late as September or October 2027, depending on your entity type.
Retirement planning is just one of many decisions to make before the calendar flips. For additional year-end tax strategies for solo business owners, 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 Steps
- Confirm who’s on your team. If anyone besides you and your spouse works enough hours to be eligible, a Solo 401(k) is off the table. Consider a SEP, SIMPLE IRA, or traditional 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.
- Run both contributions. SEP: approximately 20% of net self-employment earnings (or 25% of W-2 pay). Solo 401(k): that amount plus up to $24,500 employee deferral and catch-up if over 50.
- Decide on Roth vs pre-tax. If Roth savings or 401(k) loan access matter, Solo 401(k) is usually the practical choice.
- Check the calendar. Before December 31: open the Solo 401(k) if it fits your needs. After December 31: a SEP may be your only option for 2026, barring the sole proprietor first-year exception.
- Bring it to a pro, then open the account. Choose a provider, sign the plan documents, set up deferrals with payroll if applicable, and remember to file Form 5500-EZ annually once assets reach $250,000.
Common Mistakes I See With Solo 401(k)s and SEPs
- Opening a SEP by default. The bank offered it first, so you took it. This often leaves you $24,500 per year of contribution room unused.
- Using profit instead of W-2 pay as an S-corp owner. Contributions are based solely on your salary. Distributions do not count.
- Doubling up on the deferral. The $24,500 employee deferral limit applies across all 401(k) plans you participate in. If you also have a 401(k) at a day job, your Solo 401(k) deferrals share this limit.
- Hiring without checking the plan. Adding a first employee can disqualify you from Solo 401(k) eligibility. Consult your plan provider before extending an offer.
- Forgetting the 5500-EZ filing. Once your Solo 401(k) assets exceed $250,000, you must file Form 5500-EZ annually. Missing this can trigger significant penalties.
The Bottom Line
If you are a business of one, the Solo 401(k) is generally the strongest retirement savings vehicle available. It allows you to save more on less income, provides catch-up contribution opportunities, offers a genuine Roth option, and permits loans in emergencies. The SEP IRA rightfully earns its place when you have employees, your business profits are high enough to max out both plans, or when timing and deadlines dictate your choice.
Your business already pays you. Make sure it pays your future self too, and pick your retirement account before December 31 picks it for you.
This article is educational and does not constitute personal tax, legal, or financial advice. Contribution limits, entity type, 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, a Solo 401(k) is better. It permits a $24,500 employee deferral in addition to the same employer contribution a SEP allows, plus catch-up contributions, Roth deferrals, and loans. 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. The Solo 401(k) adds an $8,000 catch-up contribution for those aged 50 or older, increasing to $11,250 for ages 60 to 63. SEP IRAs do not offer catch-up contributions.
When is the deadline to open a Solo 401(k) for 2026?
The general deadline is December 31, 2026, to make employee deferrals for that year. However, sole proprietors with no employees who are opening their first Solo 401(k) 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 are subject to a combined $72,000 limit, and maintaining a SEP IRA alongside another retirement plan may disqualify you from using the IRS model SEP form. Most solo business owners select one account. Always consult your provider and tax advisor first.
Does a SEP IRA allow Roth contributions?
SECURE 2.0 permits Roth contributions to SEP IRAs, but many custodians have yet to offer this feature. SEP IRAs also do not allow employee deferrals. If Roth savings are important to you, a Solo 401(k) with a Roth option is typically the better choice.
