Freelancer Retirement: Solo 401(k) vs SEP-IRA (2026)

No employer means no HR department auto-enrolling you in a 401(k), no match showing up quietly every payday, and no plan administrator deciding the rules for you. If you're self-employed, building a retirement account is one more thing you have to set up yourself — and the two accounts built for exactly this, a Solo 401(k) and a SEP-IRA, aren't equivalent. At the same income, one of them usually lets you shelter thousands of dollars more. Below is what each account actually is, the real 2026 contribution limits, why the gap between them is often an exact number rather than a rough one, and what that room is actually worth in deferred tax.

The two accounts, side by side

Both are built for a self-employed person with no full-time common-law employees other than a spouse — a sole proprietor, a single-member LLC, a freelancer paid on 1099s. Past that, they work differently.

A SEP-IRA (Simplified Employee Pension) is close to the simplest retirement account the IRS offers a business owner. There's no separate employee-vs-employer contribution split — you make one contribution, calculated as a percentage of your income, and that's the whole plan. No annual filing, no plan document to draft yourself (most brokerages set one up with a form), and — this matters more than it sounds like it should — you can open a SEP-IRA and fund it as late as your tax filing deadline, including extensions. Decide in September that you want a retirement account for the year that ended the previous December, and a SEP-IRA is still on the table.

A Solo 401(k) (also called a one-participant 401(k) or individual 401(k)) splits your contribution into two pieces: an employee elective deferral, the same kind of contribution a W-2 employee makes from a paycheck, and an employer profit-sharing contribution, calculated the same way a SEP's contribution is. Stacking both is what usually lets a Solo 401(k) hold more than a SEP-IRA at the same income. The tradeoff is timing and paperwork: per IRS guidance on one-participant 401(k) plans, the plan itself has to exist — the account opened, the plan document signed — by December 31 of the tax year, even though you have until your filing deadline to actually fund it. Miss that date and you're a SEP-IRA (or nothing) for that tax year. Many providers also let a Solo 401(k) accept Roth contributions on the deferral piece and offer a loan feature against the balance — neither of which a standard SEP-IRA offers.

One more real difference, easy to miss until it applies to you: a SEP-IRA has to cover any employee who meets minimal eligibility rules (generally: age 21, three of the last five years of service, minimum compensation) at the same percentage you contribute for yourself. A Solo 401(k), by design, covers only an owner and a spouse — the moment you have another eligible employee, it stops qualifying as "solo" and the plan has to be restructured. If you're planning to hire, that's a real factor beyond the contribution math.

How much you can actually contribute in 2026

Three numbers drive both plans for 2026, all direct from the IRS:

• Employee elective deferral limit: $24,500 — the flat dollar amount you can defer from earnings into a 401(k)-type plan, Solo 401(k) included.
• Age-50-and-over catch-up: $8,000 — an addition to the deferral limit if you're 50 or older any time in the tax year, bringing the deferral to $32,500.
• Overall defined-contribution limit: $72,000 — the combined ceiling on everything going into one plan in a year (employee deferral plus employer contribution), rising to $80,000 once the catch-up applies.

A SEP-IRA only ever gets one of these three numbers: the overall $72,000 cap, applied to an employer-style contribution with no deferral piece and no catch-up. The SEP's contribution formula is 20% of your adjusted net self-employment income — not the 25%-of-compensation figure you'll see on the IRS's general SEP contribution limits page, which describes the W-2-employee version. For a sole proprietor, the circular math of computing your own "compensation" nets out to an effective 20% rate — this is standard IRS guidance for self-employed SEP contributions, and it's what the calculator below uses.

"Adjusted" net self-employment income means your net profit minus the deductible half of your self-employment tax — the same figure that lands on Schedule 1, and the same adjustment the Self-Employment Tax Calculator works out on its own. It's worth running that number first: since the SEP and Solo 401(k) contribution base both shrink as this figure shrinks, every dollar of deductible business expense — including vehicle mileage at the IRS standard rate — lowers this year's tax bill and next year's retirement room at the same time. That's not a reason to skip deductions, just a tradeoff worth knowing about.

A Solo 401(k) gets all three numbers: the flat deferral ($24,500, or $32,500 with the catch-up), plus the same 20%-of-adjusted-income employer contribution a SEP-IRA gets, all still capped by the overall limit ($72,000, or $80,000 with the catch-up).

Try it with your own numbers

Enter your net self-employment income and age, and it works out both maximums using the exact 2026 IRS figures above — the page URL becomes a shareable permalink of your inputs.

Why the Solo 401(k) usually wins at lower income

Here's the part that isn't obvious until you look at the formulas side by side: until either number hits the overall dollar cap, the gap between a Solo 401(k) and a SEP-IRA is exactly the deferral amount you qualify for — not roughly, exactly. Both plans apply the identical 20%-of-adjusted-income calculation for the employer piece; the Solo 401(k) just bolts the flat deferral on top of the same number. So at any income low enough that neither plan is capped, a Solo 401(k) beats a SEP-IRA by precisely $24,500 (or $32,500 with the catch-up) — dollar for dollar, every time.

That gap only shrinks once income climbs high enough that both plans' totals start bumping into the $72,000 (or $80,000) ceiling. Above that income, the 20% employer piece alone is enough to hit the cap on its own, so the deferral stops adding anything — both accounts land on the same number, and the Solo 401(k)'s only remaining edge is the catch-up itself, if you qualify for it. Below that income, the deferral is the entire advantage. This is why a Solo 401(k) matters most for exactly the freelancers who might assume it doesn't — solid but unspectacular income, not obviously "high earner" territory.

Two worked examples

A mid-career freelancer, $100,000 net self-employment income, age 45 (under the catch-up threshold):

• Deductible half of self-employment tax: $7,064.78
• Adjusted base: $100,000 − $7,064.78 = $92,935.22
• SEP-IRA max: 20% × $92,935.22 = $18,587.04
• Solo 401(k) max: $24,500 + $18,587.04 = $43,087.04
• The gap: $24,500.00 — exactly the deferral limit, as the math above predicts.

A freelancer earning less but old enough for the catch-up, $50,000 net self-employment income, age 50:

• Deductible half of self-employment tax: $3,532.39
• Adjusted base: $50,000 − $3,532.39 = $46,467.61
• SEP-IRA max: 20% × $46,467.61 = $9,293.52
• Solo 401(k) max: $32,500 + $9,293.52 = $41,793.52
• The gap: $32,500.00 — again, exactly the catch-up-boosted deferral.

That second example is worth sitting with: on $50,000 of net income, a Solo 401(k) can theoretically shelter $41,793.52 — over 83% of it — versus $9,293.52 in a SEP-IRA. Real life clamps this in ways the formula doesn't: you can't actually defer more than you earn after other obligations, and this calculator (like most public ones) doesn't model that floor. Treat the output as the IRS ceiling, not a spending plan.

Push income high enough and the gap disappears. At $400,000 and age 55, the SEP-IRA caps at the full $72,000 overall limit, and the Solo 401(k) — with its own cap raised to $80,000 by the catch-up — tops out at $80,000. The remaining $8,000 difference is the catch-up alone; the deferral itself stopped mattering once the employer-side 20% passed $72,000 on its own.

What the extra room is worth in taxes

A traditional (pre-tax) contribution to either plan is a deduction against this year's income tax — it does not touch your self-employment tax. That distinction trips people up: self-employment tax is calculated on Schedule SE from your net profit before any retirement contribution is subtracted, so maxing out a Solo 401(k) doesn't lower the Social-Security-and-Medicare bill the Self-Employment Tax Calculator shows you — only the income-tax side moves.

On the income-tax side, though, the deduction is real money, deferred rather than eliminated — you'll owe ordinary income tax when you eventually withdraw it, ideally in retirement at a lower rate, or sooner with a penalty if you tap it early. Take the $100,000 example above: the extra $24,500 a Solo 401(k) shelters that a SEP-IRA doesn't, at an illustrative combined 29% federal-plus-state marginal rate (24% federal, 5% state), defers $7,105.00 of income tax this year that would otherwise be due on top of everything else. Contribute the Solo 401(k)'s full $43,087.04 instead of stopping at the SEP-IRA's $18,587.04, and the deferral on the whole amount comes to $12,495.24 at that same rate — real cash that stays out of the IRS's hands until a future year, not a rate this site can quote for your actual bracket. Before deciding how much of your income to lock away rather than spend, the 1099 Take-Home Pay Calculator is a useful first stop — it shows what's actually left after self-employment tax and income tax, so you're deciding how much of that number to redirect, not the gross figure.

One more wrinkle worth knowing: under the SECURE 2.0 Act, some custodians now offer a Roth (after-tax) version of a SEP-IRA, not just a Solo 401(k) — support varies by provider, so ask before assuming either account is pre-tax-only. A Roth contribution skips this year's deduction in exchange for tax-free withdrawals later, which is a different trade than the deferral math above and depends on whether you expect your tax rate to be higher or lower in retirement.

Deadlines, paperwork, and the fine print that decides for you

The single most common way freelancers end up with a SEP-IRA by default isn't a deliberate choice — it's missing the Solo 401(k)'s December 31 plan-establishment deadline. If it's already past year-end and you haven't opened a Solo 401(k) for that tax year, a SEP-IRA (fundable up to your filing deadline, extensions included) is still available; a Solo 401(k) for that year generally isn't.

Once a Solo 401(k) is running, there's ongoing paperwork a SEP-IRA doesn't have: per the IRS, a one-participant 401(k) generally has to file Form 5500-EZ annually once plan assets hit $250,000 — not onerous, but it's a filing obligation a SEP-IRA never triggers regardless of balance.

If you're mid-year and deciding how much to route toward retirement instead of spending it, run your numbers through the Tax Set-Aside Calculator with that in mind: a retirement contribution lowers the income-tax portion of your estimate but not the self-employment-tax portion, so don't zero out your whole set-aside percentage just because you maxed a retirement plan this year — only part of what you set aside was ever going toward income tax in the first place.

Which one should you actually open

Lean Solo 401(k) if: your income is moderate enough that the flat deferral is doing real work (roughly, income where the 20%-of-adjusted-base contribution alone wouldn't already hit $72,000), you want a Roth option for at least part of your contribution, you might want to borrow against the balance later, and you can get the plan opened before December 31.

Lean SEP-IRA if: it's already past year-end and you need a plan for the prior tax year, you want zero ongoing paperwork regardless of balance, your income is high enough that both plans land on roughly the same number anyway, or you plan to bring on employees soon and don't want to restructure a Solo 401(k) later.

Either way, this is a limits comparison, not a full financial plan — it doesn't weigh investment options, fees, Roth-versus-traditional tradeoffs in depth, or how a retirement account interacts with the rest of your finances. Run the numbers, then talk to a tax professional or plan provider before you commit real money.

Methodology & sources

This guide and its calculator cover US federal rules only, for a sole proprietor or single-member LLC with no common-law employees besides a spouse — not partnerships, S-corps, or businesses with staff, which follow different rules. The adjusted contribution base is net self-employment income minus the deductible half of self-employment tax, computed the same way as this site's Self-Employment Tax Calculator. SEP-IRA and Solo 401(k) employer-contribution math both use the standard 20%-of-adjusted-base rate for the self-employed; the Solo 401(k) adds the flat elective deferral on top. Figures shown are ceilings under the IRS formulas, not a guarantee your specific plan document or income supports contributing the full amount. Nothing here is tax, investment, or financial advice — verify current-year limits directly with the IRS or a licensed professional before funding an account, since these figures are adjusted annually and this page will lag until it's updated.

The $24,500 deferral limit and $8,000 catch-up come from the IRS's own announcement, 401(k) limit increases to $24,500 for 2026, IRA limit increases to $7,500; the $72,000 overall defined-contribution limit comes from the IRS's COLA increases for dollar limitations on benefits and contributions table. Plan mechanics and deadlines are drawn from the IRS's Publication 560, Retirement Plans for Small Business and its One-Participant 401(k) Plans page.