Introduction
SEP IRA vs Solo 401k is the question almost every freelancer runs into the moment they stop scrambling for clients and start wondering where the money actually goes long-term. Both are retirement accounts built for self-employed people, both offer real tax advantages, and both get recommended constantly — but they aren’t interchangeable, and picking the wrong one can quietly cap how much you’re allowed to save every single year.
This guide breaks down what each account actually lets you contribute, where the real gap shows up, and which one tends to win depending on your income and setup. If you’ve already sorted out your business structure and have pricing that reflects your actual worth, retirement is the next place freelancers tend to leave money on the table without realizing it.
Disclaimer: this is general information, not financial or tax advice. Contribution limits and eligibility rules have real exceptions depending on your specific situation — talk to a CPA or financial advisor before opening or funding either account.
What a SEP IRA Actually Is
A SEP (Simplified Employee Pension) IRA is about as close to “set it up in an afternoon” as retirement accounts get. Most major brokerages let you open one online in minutes, with no annual filing requirement regardless of how much you have saved in it. Contributions are employer-only — as a freelancer, that “employer” is you, and you can contribute up to 25% of your net self-employment income, capped at $72,000 for 2026.
The catch is that the 25% figure is calculated after adjusting for self-employment tax, which usually works out closer to about 20% of your gross net profit in practice. There’s no separate “employee” contribution the way a 401(k) has — the entire contribution comes from that single percentage-of-income formula.
What a Solo 401(k) Actually Is
A Solo 401(k) — also called an individual 401(k) — works in two parts, the same way an employer-sponsored 401(k) does, except you’re both the employee and the employer. As the “employee,” you can defer up to $24,500 of your own income in 2026 (or up to 100% of compensation if you earn less than that), regardless of your net profit percentage. As the “employer,” you can then add up to 25% of compensation on top, subject to the same combined cap of $72,000 for 2026 (higher with catch-up contributions once you’re 50+).
This is the core of the SEP IRA vs Solo 401k gap: the Solo 401(k)’s employee deferral isn’t tied to a percentage of income at all, which means it can let you contribute far more than a SEP IRA at the exact same income level.
The Contribution Gap That Actually Matters
This is where SEP IRA vs Solo 401k stops being theoretical. A concrete example on $60,000 in net self-employment income: a SEP IRA caps you at roughly 20% of that, around $12,000. A Solo 401(k) at the same income lets you defer up to $24,500 as the “employee,” then add roughly 20% as the “employer” — landing well above the SEP figure, since the employee piece isn’t limited by the percentage formula at all.
At lower and moderate income levels specifically, the Solo 401(k) almost always lets you save more, purely because the employee deferral is a flat dollar cap rather than a percentage of anything. The gap narrows as income climbs, because the 25% employer-side math starts to dominate for both accounts once profit is high enough.
SEP IRA vs Solo 401(k): Which Wins at Your Income Level
- Under $40,000/year in net profit — a Solo 401(k) usually lets you save meaningfully more, since the flat employee deferral isn’t limited by the 25% formula that caps a SEP IRA at this income range.
- $40,000-$100,000/year — a Solo 401(k) still tends to win on pure contribution room, though the gap narrows as the employer-side percentage becomes the bigger piece of both accounts.
- Over $100,000/year, want maximum simplicity — a SEP IRA can get close to the same cap with far less paperwork, since there’s no employee/employer split to track and no Form 5500-EZ filing once assets grow past $250,000.
- Have part-time or seasonal employees — this changes the math a lot. A SEP IRA generally requires you to contribute the same percentage for every eligible employee, which gets expensive fast. A Solo 401(k) is only available if you have no common-law employees other than a spouse.
Other Real Differences Worth Knowing
- Roth option. A Solo 401(k) can offer a Roth (after-tax) option for the employee-deferral portion at most providers. A standard SEP IRA is pre-tax only, though some providers have started offering Roth SEP contributions since SECURE 2.0.
- Participant loans. A Solo 401(k) can allow you to borrow against your own balance (typically up to $50,000 or half the balance, whichever is less). A SEP IRA offers no loan provision at all.
- The backdoor Roth IRA trap. If you use, or plan to use, the backdoor Roth IRA strategy, a SEP IRA balance counts against you under the IRS pro-rata rule, making the conversion partly taxable. A Solo 401(k) balance doesn’t count toward that calculation at all, since it isn’t an IRA.
How to Actually Open One
Both accounts are easy to open at major brokerages like Fidelity, Schwab, or Vanguard, typically with no setup fee. A SEP IRA can usually be opened and funded any time up to your tax filing deadline (including extensions) for the previous year. A Solo 401(k) has a harder deadline: the account itself must be opened by December 31 of the tax year, even though you can still fund the employer-side contribution up until your filing deadline. Missing that December 31 cutoff for a Solo 401(k) means waiting until the following year — a mistake worth marking on a calendar well in advance.
Common Mistakes With Retirement Accounts
- Opening a Solo 401(k) after December 31. By far the most common and completely avoidable mistake — the account has to exist before year-end even if you fund it later.
- Defaulting to a SEP IRA without running the numbers. It’s simpler to open, so people default to it, then leave real contribution room on the table at moderate income levels where a Solo 401(k) would let them save thousands more.
- Ignoring the backdoor Roth interaction. Opening a SEP IRA while also planning backdoor Roth conversions can create an unexpected tax bill that a Solo 401(k) would have avoided entirely.
- Forgetting the employee deferral has its own deadline. The Solo 401(k) employee-deferral election generally needs to be made before year-end, separate from the employer-contribution funding deadline.
Frequently Asked Questions
Which is better for freelancers, SEP IRA or Solo 401(k)?
For most freelancers earning under roughly $100,000/year, a Solo 401(k) usually allows higher contributions because the employee deferral isn’t tied to a percentage of income. A SEP IRA can make sense for simplicity, especially at higher income where the gap narrows.
Can I have both a SEP IRA and a Solo 401(k)?
Not usefully in the same year for the same business — contribution limits are shared across employer-sponsored plans for the same self-employment income, so stacking them doesn’t let you exceed the combined cap.
What happens if I miss the Solo 401(k) December 31 deadline?
You can’t open a Solo 401(k) for that tax year anymore — the account itself must exist by December 31, though a SEP IRA can still be opened as late as your tax filing deadline for the same year.
Does a SEP IRA affect a backdoor Roth IRA?
Yes. SEP IRA balances count under the IRS pro-rata rule for backdoor Roth conversions, which can make part of the conversion taxable. A Solo 401(k) balance doesn’t create this problem since it isn’t classified as an IRA.
Do I need an accountant to set either of these up?
Not strictly — major brokerages walk you through opening either account. But given how the contribution math depends on your specific net self-employment income, a CPA is worth it at least once to confirm you’re maximizing the right account.
Final Thoughts
SEP IRA vs Solo 401(k) isn’t a decision to make based on which name sounds more familiar — the actual dollar difference in how much you’re allowed to save can be significant at moderate income levels. Run the numbers for your specific net profit before defaulting to whichever account your brokerage suggests first, and mark that December 31 Solo 401(k) deadline somewhere you’ll actually see it.
