On numerous occasions a business owner has sat across from me with a SEP-IRA already open, funded, and humming along, simply because that’s what their CPA told them to do five years ago. It’s understandable, SEP-IRAs are the default answer because they’re easy to explain in a five-minute conversation at tax time. But “easy to explain” and “best account for you” are two very different things, and for a lot of self-employed people and small business owners, that default is quietly costing them real money every single year.
SEP IRA vs. Solo 401(k): The Quick Answer
If you’re a solo operator with no employees other than maybe a spouse, a Solo 401(k) will almost always let you contribute more than a SEP-IRA at the same income level, it gives you access to a Roth option that actually works in practice, and it protects a backdoor Roth strategy if that’s part of your plan. A SEP-IRA wins on pure simplicity, and it’s still the better choice the moment you have employees you’d need to cover.
Now here’s the part most articles on this topic skip, because most of them are written by someone who’s never actually had to explain this to a client with real money on the line.
SEP IRA vs. Solo 401(k) Contribution Limits for 2026
A SEP-IRA is funded entirely by the employer side. This means that if you’re self-employed, that’s you wearing your “employer hat.” You can contribute up to 25% of compensation (for a sole proprietor or single-member LLC, the actual math nets out closer to about 20% of net self-employment income, once you account for the self-employment tax adjustment (this trips people up constantly). For 2026, the overall cap is $72,000. There’s no catch-up contribution for SEP-IRAs, regardless of your age. None. That surprises a lot of clients in their late 50s who assumed catch-up provisions applied everywhere.
A Solo 401(k) gives you two separate buckets. You can contribute as the “employee” up to $24,500 in 2026, or $32,500 if you’re 50 or older, or $35,750 if you’re 60 through 63 thanks to the newer SECURE 2.0 super catch-up. On top of that, you contribute as the “employer,” using essentially the same 25%/20% calculation as the SEP. Add both buckets together and you’re still capped by the same overall $72,000 (or $80,000, or $83,250 depending on your age bracket), but you get there with meaningfully less income, because that employee deferral bucket doesn’t care what your net self-employment income actually is.
Here’s what that looks like in practice. I’ll use a simplified example: a 45-year-old consultant netting $150,000 in self-employment income. With a SEP-IRA, the employer-only calculation caps out around $37,500. With a Solo 401(k), that same person adds the $24,500 employee deferral on top of a similar employer contribution, and can realistically get north of $60,000 into the account. Same income, meaningfully more saved, same tax deduction principle. That gap is the whole ballgame for most people below roughly $280,000–$300,000 in net self-employment income. Above that range, the two plans tend to converge toward the same overall cap anyway.
How a SEP IRA Affects a Backdoor Roth IRA
This issue is something else to keep in mind, because it’s the piece that costs sophisticated clients real money and almost nobody brings it up until it’s too late.
If you ever plan to make backdoor Roth IRA contributions, a SEP-IRA balance will work against you. The IRS treats SEP-IRAs as traditional IRA assets for purposes of the pro-rata rule, meaning your SEP balance gets lumped in with any other IRAs you own when calculating the taxable portion of a backdoor Roth conversion. If you’ve got a healthy six-figure SEP balance sitting there, that backdoor Roth strategy you thought was clean is now generating a tax bill you weren’t expecting.
A Solo 401(k), on the other hand, is a qualified plan, not an IRA. Due to this, it sits completely outside that pro-rata calculation. If backdoor Roth contributions are or might become part of your plan, this alone can be the deciding factor, full stop.
Where the SEP-IRA Still Wins
I don’t want this to read like I think SEP-IRAs are obsolete, because they’re not, and I still recommend them regularly. Disclaimer: I still have a SEP-IRA, I just can’t contribute to it anymore because I started my own Solo 401(k) last year.
The paperwork is much simpler. A SEP-IRA requires a one-page adoption form (Form 5305-SEP), no annual government filing regardless of balance size, and you can open and fully fund a SEP-IRA as late as your tax filing deadline, extensions included, for the prior year. That flexibility is real. I have clients (including myself) who don’t know their exact net income until their CPA finishes their return, and a SEP-IRA lets them make the entire decision and contribution at that point. A Solo 401(k) generally needs to be established by December 31st of the tax year for you to make an employee deferral for that year. If you miss that window and you’re limited to the employer-side contribution only, even if you fund it later.
And if you have, or think you might soon have, actual employees (not your spouse, but real W-2 employees) a SEP-IRA remains available to you, while a Solo 401(k) simply isn’t an option anymore once that happens. You’d have to cover eligible employees at the same contribution percentage as yourself, which gets expensive fast, but at least the plan still exists in that scenario.
SEP IRA or Solo 401(k): What I Recommend to Clients
If you’re truly solo, comfortable with a bit more paperwork, and your income supports it, I lean Solo 401(k) more often than not. The higher contribution ceiling at the same income, the loan feature (for plan where the plan document allows it), and the backdoor Roth protection usually outweigh the extra administrative lift.
If your income is unpredictable, you want maximum flexibility on when you decide and fund, or there’s a real chance you’ll bring on employees in the next couple of years, the SEP-IRA is still a perfectly good choice.
This is exactly the kind of decision where “it depends” isn’t a cop-out, it’s the actual answer, and it depends on specifics that are worth an actual conversation rather than a default from five years ago.
This article is for informational purposes only and does not constitute tax, legal, or investment advice. Contribution limits and rules are current as of 2026 and subject to change. Please consult your CPA or tax advisor before establishing or funding a retirement plan, as individual circumstances vary. Advisory services are offered through OneSeven. Services are provided under the name JTM Williams Capital Management, a DBA of OneSeven. OneSeven is a registered investment adviser with the U.S. Securities and Exchange Commission (SEC). Registration with the SEC does not imply a certain level of skill or training.
Have questions about which plan fits your business? Reach out anytime at Matt@JTMWilliams.com or 703.782.3110, or schedule a complimentary 15-minute call.
