The IRS's 2026 retirement-plan adjustments raised the maximum annual addition for self-employed savers to roughly $72,000, with the figure showing up in both the SEP IRA contribution ceiling and the combined employee-plus-employer cap on a Solo 401(k). On paper, the two accounts now look interchangeable. In practice, for the vast majority of sole proprietors, they are not.
The reason is not the cap. It is the formula used to reach the cap — and a single income threshold near $175,000 in net self-employment earnings that quietly separates "the account that maxes out your savings" from "the account that leaves five-figure sums on the table."
How the Two Accounts Calculate Contributions
Both plans are funded out of self-employment income, but they get there differently.
SEP IRA (2026):
- Single bucket: employer contribution only
- Limit: the lesser of 25% of eligible compensation or $72,000
- For an unincorporated sole proprietor, the effective ceiling is roughly 20% of net self-employment income after the self-employment-tax adjustment
Solo 401(k) (2026):
- Two buckets stacked together
- Employee deferral: up to $24,500 of compensation (age 50+ catch-up of $8,000 and the age 60–63 super catch-up of $11,250 are available on top)
- Employer contribution: up to roughly 20% of net self-employment income for a sole proprietor
- Combined annual addition capped at the same $72,000 figure (or higher with age-based catch-ups)
The Solo 401(k)'s employee deferral is the structural difference. It is a flat-dollar bucket that does not depend on profit. That changes the math dramatically at lower and middle income levels.
The Income Threshold That Decides Everything
Consider a sole proprietor with $60,000 in net self-employment income in 2026:
- SEP IRA contribution: roughly $12,000 (capped by the ~20% formula)
- Solo 401(k) contribution: roughly $36,000 — a full $24,500 employee deferral plus a ~$12,000 employer contribution
Same income. Same person. Triple the tax-advantaged savings under the Solo 401(k). Until net earnings climb high enough that 20% of income alone exceeds the $72,000 cap, the SEP IRA's percentage-only formula simply cannot keep pace.
The crossover sits at approximately $175,000 in net self-employment income for a sole proprietor. Above that line, both accounts are constrained by the same hard dollar cap and the contribution capacity becomes effectively identical. Below it, the Solo 401(k) wins, often by a wide margin.
When the SEP IRA Still Makes Sense
Despite the contribution gap, the SEP IRA is not obsolete. Its design carries a few practical advantages that matter at higher earnings or in specific business structures:
- Lower administrative overhead. A SEP IRA can be opened and funded right up until the tax-filing deadline (including extensions). A Solo 401(k) generally must be established by December 31 of the contribution year, even if it is funded later.
- No annual filing requirement at most asset levels. Solo 401(k) plans with more than $250,000 in assets trigger an annual Form 5500-EZ filing, a paperwork burden the SEP IRA avoids entirely.
- Cleaner option when employees are added. A SEP IRA's pro-rata employer contribution rule is straightforward when a one-person shop hires its first W-2 employees; a Solo 401(k), by definition, can no longer remain "solo" once non-spouse employees are eligible.
For a self-employed worker whose income consistently sits above the $175,000 crossover and who values simplicity over flexibility, the SEP IRA's lighter footprint can outweigh the Solo 401(k)'s structural advantages.
Practical Takeaways for 2026 Planning
- Run the actual contribution math, not the headline cap. Two accounts with the same $72,000 ceiling can produce wildly different contribution capacity at the same income.
- Know your number. If your net self-employment income is likely to sit below roughly $175,000 in 2026, the Solo 401(k) is almost certainly the more generous container.
- Watch the calendar. A Solo 401(k) that exists only on January 2 cannot accept 2025 contributions. If a switch makes sense, the December 31 establishment deadline is the binding constraint.
- Coordinate with the Roth catch-up rule. Beginning in 2026, employees of their own business whose prior-year FICA wages exceeded $150,000 must direct any age-50+ catch-up into a Roth bucket — a planning wrinkle the SEP IRA does not face but also cannot accommodate.
The 2026 limits give self-employed savers more room than ever. The harder question — and the more consequential one — is which container actually unlocks it.
Sources: Internal Revenue Service, Fidelity Investments, Kiplinger, IRA Financial, Self-Employed Quarterly