SEP IRA vs Solo 401(k): Which Saves More?

The Mistake I Made (and You Might Be Making)

When I started looking at retirement accounts for self-employed people, I picked the SEP IRA because it was the first one I understood. Fidelity let me open one in about 10 minutes. No paperwork beyond the online application. No plan documents. I could contribute up to 25% of my net self-employment income, and the contribution was tax-deductible. Simple, fast, done.

What I didn't realize — and what nobody explained clearly until I stumbled into an r/personalfinance thread at 1 AM — is that the Solo 401(k) would have let me contribute dramatically more money at my income level. Not a little more. Not marginally more. At $50,000 in net self-employment income, the Solo 401(k) allows roughly $33,800 in contributions. The SEP IRA allows roughly $9,300. The gap is the flat $24,500 employee deferral, and the tax deduction on it at the 22% bracket is about $5,390 I left on the table.

I'm sharing this because the SEP IRA is what most people default to: it's simpler, it's faster to open, and every brokerage pushes it as the go-to retirement account for freelancers. It's not a bad choice. But if you have the income to save aggressively and you want to maximize your tax deduction, it might be the wrong one. The difference comes down to a structural feature of 401(k) plans that SEP IRAs don't have, and understanding that feature takes about three minutes.

How Each Account Works

Both accounts are tax-deferred retirement accounts for self-employed people. Contributions reduce your taxable income now, and you pay income tax when you withdraw in retirement. Both have the same early withdrawal penalty (10% before age 59 1/2, with exceptions). Both can be opened at a major brokerage with no account fees; Fidelity and Schwab cover both types (Vanguard left the solo 401(k) business, which is its own story).

The SEP IRA works like a turbocharged traditional IRA. You, as the employer, contribute up to 25% of your net self-employment income (net profit minus half of SE tax). That's it. One contribution type. One calculation. The maximum contribution in 2026 is $72,000, but you'd need roughly $377,000 in net profit to hit that ceiling, because the 25% headline rate works out to 20% of net earnings once the SE-tax adjustment is applied. For most side hustlers, the effective limit is much lower because it's capped at 25%.

The Solo 401(k) (also called an Individual 401(k) or one-participant 401(k)) has two contribution components. As the employee, you can defer up to $24,500 of your compensation (the 2026 employee contribution limit). On top of that, as the employer, you can contribute up to 25% of net self-employment income. The total of both can't exceed $72,000 (or $80,000 if you're 50 or older, thanks to the catch-up contribution).

That employee deferral component is the whole game. It's an additional $24,500 that the SEP IRA simply doesn't have. At lower income levels, where the 25% employer contribution doesn't amount to much, the employee deferral makes the Solo 401(k) dramatically more powerful.

Contribution Limits at Every Income Level

The caps are the whole comparison, which is a strange fact on its own; Money Stack Exchange's “Why is there a cap on 401k contributions?” has 39 votes precisely because the limits, not the investments, decide what these accounts are worth. This table shows the maximum contribution for each account type at various net self-employment income levels. The SEP column uses the 25%-of-adjusted-net formula. The Solo 401(k) column combines the $24,500 employee deferral with the employer contribution. All figures are for 2026, for filers under age 50.

From $50,000 up, the difference column is always the flat $24,500 employee deferral: the SEP IRA has only the employer contribution (effectively 20% of adjusted net), while the Solo 401(k) stacks the deferral on top of that same employer piece. The $30,000 row is the exception that proves a different rule: total contributions can never exceed your compensation, so the account caps out at your adjusted net income itself. The gap is structural, not proportional, and it matters most as a percentage of income at lower levels.

Why the Gap Is So Large at Lower Incomes

Look at the $30,000 row. With a SEP IRA, you can shelter $5,576, about 18.6% of your income. With a Solo 401(k), you can shelter $27,880, about 93% of your income (the binding cap at this level is your own compensation, not the account rules). Obviously, most people making $30,000 can't save 93% of their income. But the point is that the Solo 401(k) gives you the option. If you have other income (a W-2 job, a spouse's salary) and your side hustle income is supplemental, you might actually be able to max out that contribution and reduce your tax bill substantially.

At $50,000, the SEP allows $9,293 in contributions. The Solo 401(k) allows $33,793. If you contributed the Solo 401(k) max, you'd reduce your taxable income by an additional $24,500 compared to the SEP. At the 22% marginal tax rate, that's roughly $5,390 in tax savings. At the 24% bracket, it's $5,880. These numbers compound: $5,000 per year invested at 7% annual return grows to about $90,000 over 12 years. The choice of account type has real long-term consequences.

At higher income levels ($150,000+) the gap becomes less dramatic as a percentage. The SEP already shelters $27,881, and the Solo 401(k) shelters $52,381. Both are meaningful numbers. The employee deferral is still valuable, but the proportional difference shrinks because the 25% employer contribution is doing more of the heavy lifting.

The Case for the SEP IRA

I opened a SEP IRA, and despite the contribution limit difference, I don't regret it. The reasoning:

The SEP IRA can be opened and funded as late as your tax filing deadline, including extensions. That means if you file an extension for your 2026 return, you have until October 15, 2027 to open a SEP IRA and make your contribution. This is incredibly useful if you're not sure whether you'll have the cash to contribute until you see your full-year numbers. I opened mine in March 2024, funded it with my 2023 contribution, and reduced my tax bill for a year that had already ended. No advance planning required.

The Solo 401(k) used to have a hard December 31 deadline, and most articles still repeat it. SECURE 2.0 changed the rule for sole proprietors: for your first plan year, you can now open the account after year-end and still make that year's employee deferral, as long as both happen by the unextended filing deadline (April 15). The catch is the word unextended: a SEP rides along with an October extension, a first-year solo deferral does not, and from the second year on your deferral elections are back on a calendar-year clock. So the SEP still wins on pure procrastination-proofing. But the gap is months narrower than the old advice says, and the confusion is common enough that the deadline question fills its own forum threads:

“Solo 401k as a sole-proprietor - opening/funding deadlines”r/tax, 2026 (a thread title, and a genre)

The SEP IRA also has zero paperwork beyond the initial account opening. No plan document to maintain. No annual filing requirement, ever, regardless of account balance. You open it, you contribute to it, you invest the money. The brokerage handles the rest. For someone who wants the tax benefit with the absolute minimum administrative burden, the SEP is hard to beat.

And then there's the hiring question. If you ever bring on employees, the SEP IRA accommodates that without restructuring. You'd need to contribute the same percentage for employees as you contribute for yourself, which is a cost, but the account structure doesn't change. A Solo 401(k) is specifically for businesses with no full-time employees (other than you and your spouse). Hire someone, and you need to convert to a standard 401(k), a process with real administrative cost and complexity.

The Case for the Solo 401(k)

The math speaks for itself. If you can contribute more, you shelter more income, you pay less in taxes today, and you build more retirement wealth over time. The Solo 401(k)'s employee deferral is a feature that the SEP IRA fundamentally cannot match.

Beyond the contribution limits, the Solo 401(k) has one other significant advantage: Roth contributions. Many Solo 401(k) plans allow you to designate your employee deferrals as Roth contributions, meaning you contribute after-tax dollars that then grow tax-free forever. SEP IRAs gained a Roth option on paper with SECURE 2.0, but most major brokerages still haven't rolled it out, so in practice the Solo 401(k) is where the real Roth flexibility lives. If you're young, in a lower tax bracket now than you expect to be later, and want tax-free growth, the Solo 401(k)'s Roth feature is a major differentiator.

The Solo 401(k) can also allow loans against the account balance (up to $50,000 or 50% of the balance, whichever is less) if the plan document provides for it. One catch I want to be straight about: the free standard plans at Fidelity and Schwab both leave loans out of their documents, so borrowing access means paying for a custom-document provider. You repay yourself with interest, and the interest goes back into your account. This isn't a feature you want to use casually (retirement money should stay retirement money), but as a last-resort liquidity option, it exists. SEP IRAs don't allow loans. Your only option for accessing SEP money early is a withdrawal with the 10% penalty.

The setup is more involved than a SEP. You need to adopt a plan document, which the big brokerages provide for free (Fidelity and Schwab both have prototype plans). You'll fill out more paperwork at account opening: the plan document, an adoption agreement, and the standard brokerage application. It's maybe 30-40 minutes versus 10 for a SEP. Not prohibitive, but it requires a small amount of advance planning.

The Complications

The W-2 job question. If you have a W-2 job and a side hustle, things get more complicated. Your employee deferral limit ($24,500 in 2026) is a combined limit across all your 401(k) plans. If you already defer $15,000 into your employer's 401(k), you can only defer $9,500 into your Solo 401(k). The employer contribution (25% of net SE income) is separate and not affected by your W-2 plan. This matters a lot. I've seen people assume they can defer the full $24,500 into a Solo 401(k) on top of their work 401(k), and that's not how it works. The community answer that gets it right, from a thread on exactly this situation:

“If you get a W2 job later, you can absolutely keep both the Solo 401k and your new employer’s 401k.”r/tax, 2026

Keeping both is fine. It's the deferral limit that's shared, not the accounts.

The Form 5500 threshold. Once your Solo 401(k) balance exceeds $250,000, you must file Form 5500-EZ with the IRS annually. It's not a difficult form (maybe 15 minutes with your year-end balance and contribution numbers), but it's an annual obligation that doesn't exist with a SEP IRA. For most side hustlers starting out, this is years away. But if you're contributing aggressively, $250,000 comes faster than you'd think, especially in a good market.

The spouse consideration. If your spouse works in your business, they can also participate in the Solo 401(k) with their own $24,500 employee deferral. This effectively doubles the household contribution potential. A SEP IRA allows spousal contributions too, but only at the 25%-of-compensation level, so the Solo 401(k) advantage doubles for couples who both work in the business.

Provider limitations. Not all brokerages offer Solo 401(k) plans with the same features, and the market just shifted: Vanguard exited the solo 401(k) business in 2026, handing its plans to Ascensus. Fidelity and Schwab both offer free Solo 401(k)s with Roth options; neither free standard plan offers participant loans (that takes a paid custom-document provider). Newer players are filling the gap; the provider comparison covers who offers what now. If you want the full feature set, stick with a provider that documents it. If you just want the contribution limits, most will do.

How to Decide

The forum version of this entire article is a six-word thread title:

“Is it worth it to open solo 401k?”r/tax, 2026

I've been sitting with this decision since I realized the Solo 401(k) would let me shelter more. How I've come to think about it:

If you want simplicity and flexibility above all else — open a SEP IRA. You can do it right now, fund it whenever you want (up to your tax filing deadline), and never think about paperwork again. The contribution limits are lower, but "lower" still means 25% of your net SE income, which is a meaningful tax deduction. I contributed $8,300 to my SEP for 2025, and it saved me roughly $1,826 in taxes. That's not nothing.

If you want to maximize tax-deferred savings and you have the income to contribute more than 25% — open a Solo 401(k). The $24,500 employee deferral on top of the employer contribution gives you substantially more room to shelter income. The setup takes 30-40 minutes instead of 10, and outside the first-year grace SECURE 2.0 added for sole proprietors, deferral elections run on a calendar-year clock. Those are manageable, mostly one-time costs. The annual math difference can be $5,000+ in tax savings, compounding year over year.

If you're not sure and the year is almost over: you have more room than the old advice says. A first-year solo 401(k) can now be opened after year-end (up to April 15) under SECURE 2.0, so December 31 is no longer a door slamming shut. If even April feels tight, open the SEP now, take the deduction, and revisit next year. You can contribute to the SEP for the current year and the Solo 401(k) for the next; having both accounts is allowed, you just can't double-dip on employer contributions for the same year.

What I'm planning to do: I'm going to open a Solo 401(k) before December 31 of this year to have it in place for 2027. My income is reaching the level where the extra $24,500 in contribution room translates to real tax savings. I'll keep my SEP IRA for the existing balance and stop contributing to it once the Solo 401(k) is active. The SEP served me well for three years. The Solo 401(k) is the next step for where I'm going.

If you're still in the early stages of side hustling and the contribution limit difference doesn't apply (because you can't save $24,500 on top of your employer contribution anyway), the SEP IRA is the better choice. Simpler, faster, and the limits won't constrain you until your income grows. Save the Solo 401(k) for when you actually bump up against the SEP's ceiling. For most side hustlers under $40,000 in net SE income, that day hasn't arrived yet.

Bruce Samuels

Personal Finance Writer

Bruce opened a SEP IRA because it was easy, then spent six months wishing he'd opened a Solo 401(k) instead. He's fixing that this December. He writes about side hustle finances from DeSoto, Texas, and his biggest financial regret is not starting retirement contributions two years earlier.

Bruce Samuels is a pen name; MoneySavvyHQ is written and fact-checked by a small editorial team, none of whom are CPAs. How we work.

Once you have chosen Solo 401k: Solo 401k Providers 2026 (After Vanguard’s Exit), the provider comparison for the account type you picked.