Solo 401(k) vs SEP IRA 2026: A SEP Needs $124,162 More Profit to Reach the Same Ceiling
Both cap at $72,000 in 2026. Computed from the IRS formulas, a Solo 401(k) reaches that ceiling at $252,316 of net profit and a SEP IRA at $376,478 — and the advantage is a flat $24,500 for most of the range.
Both share a $72,000 total limit for 2026 (the section 415(c) cap), but they reach it at very different incomes: a Solo 401(k) at $252,316 of net profit, a SEP IRA not until $376,478. A Solo 401(k) also adds an $8,000 catch-up at 50+ ($11,250 at ages 60–63), raising its ceiling to $80,000 or $83,250; a SEP IRA has no catch-up.
Get new posts in your inbox
No spam, unsubscribe anytime.
About the Author
Sujit KarkiFinance Researcher & Market Analyst
Independent finance researcher and market analyst with expertise in macroeconomics, equity markets, and personal finance. I help regular investors make better-informed decisions through rigorous, data-driven analysis.
Both cap at $72,000 for 2026; the Solo 401(k) adds catch-up contributions on top.
Solo 401(k) employee deferral is $24,500 in 2026.
A Solo 401(k) reaches the $72,000 cap at $252,316 of net profit; a SEP IRA needs $376,478.
Between roughly $40,000 and $252,000 of profit the Solo 401(k) advantage is a flat $24,500.
SEP IRA wins on simplicity and a later setup deadline — good for last-minute filers.
If you earn 1099 income — freelancing, consulting, a real side hustle — the retirement account you pick can change your tax bill by thousands of dollars. The two workhorses are the Solo 401(k) and the SEP IRA. They land at the same $72,000 ceiling in 2026, which makes people assume they're interchangeable. They aren't. The difference is how you climb to that ceiling, and on modest income it isn't close.
Same ceiling, different ladder
For 2026 both plans max out at $72,000 — that's the section 415(c) annual-addition limit. But they get there differently.
A SEP IRA is funded entirely by the "employer" (you). The limit is 25% of compensation, which for a sole proprietor works out to roughly 20% of net self-employment earnings after you back out the deduction for half your self-employment tax. No employee piece, no catch-up.
A Solo 401(k) has two buckets: an employee deferral of up to $24,500 in 2026, plus employer profit-sharing of up to 25% of compensation, up to the same $72,000 combined. And it allows catch-up contributions: $8,000 at 50+, or an enhanced $11,250 for anyone who turns 60, 61, 62, or 63 in 2026.
Why income level decides it
Both plans are defined entirely by statute, so this isn't a matter of judgement — the crossover is a closed-form consequence of four IRS figures and can be stated to the dollar. I computed the whole curve rather than quoting a round number for it (the script is published, as is the dataset below).
Net profit
SEP IRA max
Solo 401(k) max
Solo advantage
$40,000
$7,435
$31,935
$24,500
$60,000
$11,152
$35,652
$24,500
$100,000
$18,587
$43,087
$24,500
$150,000
$27,881
$52,381
$24,500
$200,000
$37,177
$61,677
$24,500
$250,000
$47,043
$71,543
$24,500
$275,000
$51,976
$72,000
$20,024
$300,000
$56,909
$72,000
$15,091
$350,000
$66,775
$72,000
$5,225
$400,000
$72,000
$72,000
$0
Two things fall out of that table that the usual write-up misses.
The advantage is flat, not shrinking. From about $40,000 of profit — the point where your net earnings can actually absorb the full deferral — all the way to $252,316, the Solo 401(k) lets you contribute exactly $24,500 more. Not proportionally more. The same $24,500, every year, whether you profit $50,000 or $250,000. It is simply the employee deferral, which the SEP has no equivalent of.
The convergence point is much higher than usually quoted. A Solo 401(k) reaches the $72,000 ceiling at $252,316 of net profit. A SEP IRA does not get there until $376,478 — it needs $124,162 more profit to arrive at the identical ceiling. Anywhere below that, the SEP is leaving room on the table.
Why $360,000 is the number that ends it
The SEP catches up at exactly $360,000 of net earnings, and that is not a coincidence. $360,000 is the section 401(a)(17) compensation limit for 2026, and 20% of it is $72,000 — precisely the section 415(c) cap. Two limits set by different statutes and adjusted separately happen to be calibrated so that a SEP's maximum lands on the overall maximum at exactly the point where compensation stops counting. The script checks that identity still holds each year and says so loudly if a future adjustment breaks it.
Below the crossover the Solo 401(k) is unambiguously more generous; above it the two are identical and the SEP's simpler paperwork is a real advantage for no cost in contribution room.
Pro Tip
If you have a W-2 job with a 401(k) and a side hustle, your $24,500 employee deferral limit is shared across all 401(k)s — you don't get a fresh $24,500 in the Solo plan. But the employer profit-sharing side is separate for each plan, so a Solo 401(k) can still add real room on top of what you're already deferring at your day job.
The deadlines that trip people up
This is where people lose money by accident. To make 2026 contributions to a Solo 401(k), the plan must be established by December 31, 2026. Miss that date and the door is closed for the year, even though you can still fund the account you already opened after year-end.
A SEP IRA can be opened and funded up to your tax-filing deadline, including extensions — as late as October 2027 for a 2026 contribution if you file an extension. So if it's December and you don't have a plan yet, the Solo 401(k) is your last call; if it's spring and you're scrambling, the SEP is your rescue plan.
Roth, loans, and paperwork
The Solo 401(k) usually offers a Roth option and permits plan loans, typically up to $50,000. The SEP IRA has no Roth option at most custodians and no loan provision. On administration, the SEP wins: one form, no annual filing until assets hit $250,000. A Solo 401(k) is more paperwork and requires filing Form 5500-EZ once assets cross that same $250,000 threshold.
I'll name the counterargument: if you might hire employees beyond a spouse, the Solo 401(k) stops being available, and a SEP (or a different plan entirely) becomes the practical choice. Pick for where your business is going, not just where it is today.
How I calculated this: SEP-IRA max = 25% of net self-employment earnings (after the deduction for half your self-employment tax), capped at the $72,000 2026 limit. Solo 401(k) max = your employee elective deferral ($24,500, or $32,500 with the 50+ catch-up) plus the same 25%-of-net-earnings employer contribution, combined still capped at $72,000 — the gap between the two is that employee-deferral piece, which is why a solo 401(k) usually wins at lower income and the two converge as income rises. Figures are the 2026 IRS limits cited below.
Interactive · see which plan lets you save more
Solo 401(k) vs SEP IRA: your 2026 max contribution
Net self-employment income$60,000
Your age40
At $60,000 of net income, a Solo 401(k) lets you save $24,500 more than a SEP IRA this year.
SEP IRA max
$0
Solo 401(k) max
$0
Estimate only, not tax advice; assumes a sole proprietor / single-member LLC. S-corp math differs.
Solo 401(k) vs SEP IRA max contribution — data table
Net income
SEP IRA max
Solo 401(k) max
$40,000
$9,294
$33,794
$60,000
$13,940
$38,440
$120,000
$27,881
$52,381
$200,000
$46,468
$70,968
Methodology
The arithmetic, from IRS Publication 560's deduction worksheet. Net earnings from self-employment are net profit less one-half of the deductible SE tax. The employer contribution rate is not 25% but 0.25 / 1.25 = 0.20, because a sole proprietor's own compensation is itself reduced by the contribution — this is the step most write-ups skip, and it is why a SEP on $100,000 of profit funds $18,587 rather than $25,000. Net earnings are then capped at the section 401(a)(17) compensation limit, and both plans' totals at the section 415(c) limit.
SE tax is 15.3% on 92.35% of net profit, with the 12.4% Social Security half stopping at the $184,500 wage base and the 2.9% Medicare half uncapped. The additional 0.9% Medicare tax above $200,000 is included in SE tax but excluded from the one-half deduction, per section 164(f).
The four statutory figures, each quoted from an IRS page rather than a secondary source: elective deferral $24,500, section 415(c) annual additions $72,000, section 401(a)(17) compensation limit $360,000, Social Security wage base $184,500. All four are linked in the sources below.
Verification. The script recomputes SE tax at $100,000 against a hand-derived figure and refuses to publish if they disagree. It also asserts the calibration described above — that 20% of the compensation limit equals the 415(c) cap exactly — and reports loudly rather than silently if a future year's adjustments break it, because the entire "$360,000 ends it" framing depends on that identity holding.
What this does not model. A sole proprietor on Schedule C, under 50, with no employees. An S-corp owner's base is W-2 wages rather than net profit, which changes everything. Catch-up contributions raise both ceilings and move both crossovers. State tax, the QBI deduction, and hiring anyone beyond a spouse all affect the decision without affecting these ceilings.
Here's What I'd Actually Do
Estimate your 2026 net self-employment income. That single number drives the decision more than anything else here.
If it's under $252,316 and you want to save aggressively, open a Solo 401(k) — before December 31, 2026. Below that figure the SEP cannot reach the same ceiling no matter what you do.
If you're time-crunched or want zero paperwork, use a SEP IRA and take advantage of the later setup deadline.
Decide Roth vs. pre-tax deliberately. If you expect higher future tax rates, the Solo 401(k)'s Roth bucket is worth having even if it's not required.
If you have a day-job 401(k), coordinate the $24,500 deferral across both plans so you don't accidentally over-contribute.
Not financial advice — talk to a CPA about your entity type before you fund anything.
Frequently Asked Questions
Both share a $72,000 total limit for 2026 (the section 415(c) cap), but they reach it at very different incomes: a Solo 401(k) at $252,316 of net profit, a SEP IRA not until $376,478. A Solo 401(k) also adds an $8,000 catch-up at 50+ ($11,250 at ages 60–63), raising its ceiling to $80,000 or $83,250; a SEP IRA has no catch-up.
This is educational content, not financial or tax advice. I'm a researcher, not your advisor, and I don't know your business structure or tax situation. Rules and limits change. Talk to a CPA or financial advisor before opening or funding a retirement plan. See the full disclaimer.
Sujit Karki|||8 min read