QUICK ANSWER
For most self-employed owners with no employees, the Solo 401(k) beats the SEP IRA in 2026 — it lets you contribute more at lower income levels, offers a Roth option, and allows loans, while the SEP only pulls ahead on simplicity. The math is straightforward: a Solo 401(k) combines an employee deferral of up to $24,500 with an employer contribution of up to 25% of compensation, while a SEP IRA gives you only the 25% employer piece. A consultant netting $80,000 can shelter roughly $39,000 in a Solo 401(k) versus about $15,000 in a SEP. Choose the SEP if you have eligible employees, want five-minute setup, or routinely decide on contributions only at tax-filing time.
Key Takeaways
- Same ceiling, different ladders — both plans cap total contributions at $72,000 for 2026, but the Solo 401(k) reaches it at far lower income because of the employee deferral layer.
- Catch-up favors the Solo 401(k) — owners 50 and older can add a catch-up deferral of $8,000, and those aged 60 to 63 get an enhanced catch-up; SEP IRAs have no catch-up at all.
- Employees change everything — a SEP requires contributing the same percentage for eligible employees as for yourself, and a Solo 401(k) is off the table entirely once you hire non-spouse W-2 staff.
- Deadlines differ in one key way — a Solo 401(k) must generally exist by year-end to capture employee deferrals for that year, while a SEP can be opened and funded as late as your extended filing deadline.
Contribution Limits: Where the Solo 401(k) Wins
A SEP IRA allows employer contributions of up to 25% of W-2 compensation — or roughly 20% of net self-employment earnings after the self-employment tax adjustment for sole proprietors — capped at $72,000 for 2026. That single lever means low-to-mid six-figure earners leave a lot of room unused. The Solo 401(k) stacks two levers: you defer up to $24,500 of compensation as the employee (Roth or pre-tax), then add the same 25% employer contribution on top. A sole proprietor with $100,000 of net earnings can put away roughly $43,000 in a Solo 401(k) versus about $18,500 in a SEP. The gap only closes around $330,000 of compensation, where both plans hit the $72,000 ceiling — which is exactly why high earners are the only group for whom the SEP is mathematically equivalent.
Setup, Paperwork, and Ongoing Administration
This is the SEP’s home turf. Opening one takes minutes at any major brokerage, there is no annual filing, and you can create and fund it after year-end — up to your tax deadline including extensions — once you know exactly what the business earned. A Solo 401(k) requires a plan document, and while brokerages provide free prototype plans, you take on two obligations: the plan generally must be established by December 31 to allow that year’s employee deferrals, and once plan assets exceed $250,000 you must file Form 5500-EZ each year. Miss that filing and penalties accrue quickly, though the IRS late-filer program caps the damage if you catch it yourself. Neither plan requires discrimination testing when it covers only you and a spouse.
Flexibility: Roth, Loans, and Employees
The Solo 401(k) offers three features a SEP cannot match. First, Roth deferrals: you can direct your $24,500 employee contribution to a Roth account, locking in tax-free growth — valuable in low-income years when your marginal rate is temporarily down. Second, loans: most Solo 401(k) plan documents permit borrowing up to 50% of the balance or $50,000, whichever is less, which functions as an emergency credit line no IRA can offer. Third, no pro-rata headaches: SEP balances count against you in backdoor Roth IRA conversions, a real issue for consultants above the Roth income limits. The SEP counters with one structural advantage — it works when you have employees. You must contribute the same percentage of pay for every eligible employee (generally those 21 or older who worked for you in three of the last five years), which gets expensive, but it is at least available; a Solo 401(k) simply cannot cover a workforce beyond you and your spouse.
Verdict: Which Should You Pick?
Pick the Solo 401(k) if you are a true solo operator (or work only with your spouse) and earn under roughly $330,000 — the higher contribution room, Roth option, and loan feature outweigh the modest paperwork. Pick the SEP IRA if you have eligible employees, if you want to make a prior-year contribution after December 31, or if you value zero administration above all else. Plenty of owners run a hybrid path: start with a SEP in the scramble of the first profitable year, then open a Solo 401(k) the following January and roll the SEP into it.
| Feature | SEP IRA | Solo 401(k) |
|---|---|---|
| 2026 max contribution | 25% of compensation, up to $72,000 | $24,500 deferral + 25% employer, up to $72,000 |
| Catch-up (50+) | None | $8,000 (more at ages 60–63) |
| Roth option | Limited availability | Yes, on deferrals |
| Loans | No | Yes, up to $50,000 |
| Works with employees | Yes (equal % required) | No (owner and spouse only) |
| Setup deadline | Tax deadline incl. extensions | Generally Dec 31 for deferrals |
| Annual filing | None | Form 5500-EZ above $250K assets |
Recommended Resources
TurboTax Home & Business 2025 — Calculates your maximum SEP or Solo 401(k) contribution from your Schedule C numbers and shows the tax savings before you fund the plan.
Accounting All-in-One For Dummies — Explains how retirement contributions flow through your books and tax return, including the self-employment earnings calculation that trips up first-time SEP funders.
Frequently Asked Questions
Can I contribute to both a SEP IRA and a Solo 401(k) in the same year?
Technically yes, but for the same business it rarely helps, because the plans share the same employer contribution limit — you cannot double up to $144,000 by opening both. Contributions from one employer aggregate under a combined cap, so a SEP plus a Solo 401(k) funded by the same LLC still tops out at $72,000 total for 2026 (plus catch-up if you qualify). Where dual plans genuinely pay off is with genuinely separate income streams. If you have a W-2 day job with a 401(k) and a side consultancy, you can max the employee deferral at work and still make employer contributions to a SEP or Solo 401(k) funded by the side business — the $24,500 deferral limit is per person across all plans, but the employer limit is per unrelated employer. That combination lets a well-paid employee with a strong side business shelter well over $100,000 in a single year. One caution: the IRS controlled-group rules treat businesses under common ownership as one employer, so you cannot split your own company in two to double the cap. If your situation involves multiple entities, spend an hour with a CPA before funding anything — unwinding excess contributions involves excise taxes and amended returns, and it is far cheaper to get the plan design right up front.