Yes, you can have both a SEP IRA and a 401(k) in the same year. The arrangement works because the IRS ties each plan to a different pot of compensation: the 401(k) runs off W-2 wages from an employer, and the SEP IRA runs off net earnings from self-employment. As long as genuine, separate earned income supports each plan, you can fund both and take the tax benefits of both.
What actually limits you is not the existence of two plans but two IRS ceilings that apply across them, plus one aggregation rule that reshapes the math when you control both sponsoring businesses.
Why Both Plans Can Exist at Once
A 401(k) and a SEP IRA coexist because the IRS treats them as separate accounts tied to separate compensation. Your 401(k) contributions come out of W-2 wages from an employer. Your SEP IRA contributions are based on net earnings from self-employment, the income you report on Schedule C or receive as a partner. One paycheck does not bleed into the other plan’s calculations.
The most common setup is someone with a full-time W-2 job who also runs a side business. The W-2 employer sponsors the 401(k). The side business funds the SEP IRA. The same structure works if you own two businesses organized differently, or in certain cases where a single entity generates both W-2 wages and Schedule C income for you.
2026 Contribution Limits
Two ceilings govern how much can go into defined contribution plans each year. You need both before the interaction makes sense.
Elective Deferral Limit
The elective deferral limit caps what you personally contribute from your paycheck to 401(k), 403(b), and similar salary-deferral plans. For 2026, that limit is $24,500 across all such plans combined. If you happen to participate in two employers’ 401(k) plans, you share the $24,500 between them; you don’t get $24,500 at each one.1Internal Revenue Service. Retirement Topics – 401(k) and Profit-Sharing Plan Contribution Limits
SEP IRA contributions are not elective deferrals. They are classified as employer contributions, even when you’re both the employer and the employee. SEP IRA money therefore does not count against the $24,500 cap at all.
Annual Additions Limit
The annual additions limit (Section 415(c)) caps the total of all contributions to a single defined contribution plan in a year: your deferrals, employer matching or profit-sharing contributions, and any forfeitures allocated to your account. For 2026, the ceiling is $72,000 per plan.2Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living Catch-up contributions don’t count against this figure.3eCFR. 26 CFR 1.415(c)-1 – Limitations for Defined Contribution Plans
Employer contributions to a SEP IRA cannot exceed the lesser of 25% of the employee’s compensation or $72,000 for 2026.4Internal Revenue Service. SEP Contribution Limits (Including Grandfathered SARSEPs) If you’re self-employed, the effective ceiling drops to roughly 20% of net self-employment earnings, because the IRS requires you to reduce net income by both the deductible half of self-employment tax and the contribution itself before applying the 25% rate. The circular math produces an effective maximum near 20%.5Internal Revenue Service. Self-Employed Individuals: Calculating Your Own Retirement Plan Contribution and Deduction
How the Limits Interact Across the Two Plans
When the 401(k) and the SEP IRA are sponsored by truly unrelated businesses, each plan gets its own $72,000 annual additions limit. Your W-2 employer’s 401(k) can receive up to $72,000 in combined deferrals and employer contributions, and your self-employment SEP IRA can separately receive up to $72,000 (or roughly 20% of net earnings, whichever is less). The only ceiling you share across both is the $24,500 elective deferral limit.
A practical example: you earn $200,000 at a W-2 job and $80,000 of net self-employment income on the side. You defer $24,500 into your employer’s 401(k). Your employer adds a $10,000 profit-sharing contribution, bringing 401(k) annual additions to $34,500. Separately, you contribute roughly $16,000 to your SEP IRA (20% of $80,000). Total for the year lands around $50,500, before any catch-up.
When the Two Businesses Are Related
The math changes when you control both the business sponsoring the 401(k) and the business funding the SEP IRA. Under IRC Section 414(b) and 414(c), businesses under common ownership or control are treated as a single employer for retirement plan purposes.6Office of the Law Revision Counsel. 26 USC 414 – Definitions and Special Rules The $72,000 annual additions limit is then shared across the plans, not stacked.
A common approach in that scenario: max your $24,500 elective deferral into the 401(k) first. That leaves $47,500 of the combined $72,000 to split between employer contributions to the 401(k) (profit-sharing) and contributions to the SEP IRA. Where the split lands depends on each plan’s compensation-based limits. If your self-employment income is $100,000, your SEP IRA tops out around $20,000, leaving about $27,500 of capacity for a corporate profit-sharing contribution to the 401(k).
This is where owners get into trouble. Treating the entities as separate for contribution purposes when the IRS views them as one employer can push you past the combined limit and trigger penalties.
Catch-Up Contributions
If you’re 50 or older by the end of the tax year, you can add an $8,000 catch-up to your 401(k) in 2026 on top of the $24,500 elective deferral, bringing your personal deferral ceiling to $32,500.7Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
SECURE 2.0 added a higher tier for participants aged 60 through 63. In 2026, those individuals can contribute an extra $11,250 instead of $8,000, pushing their total elective deferral ceiling to $35,750. Once you turn 64, you drop back to the standard catch-up.
Catch-up dollars are excluded from the $72,000 annual additions limit, so they don’t reduce the room available for employer contributions. SEP IRAs have no catch-up provision. If you want catch-up dollars in the mix, they have to go through the 401(k) side.
Deadlines and Timing
The two plans run on different clocks, and that’s part of why combining them is useful.
Your 401(k) elective deferrals happen during the calendar year, deducted from paychecks as you go. The employer’s profit-sharing contribution to the 401(k) has a longer window and can be made up to the business’s tax filing deadline, including extensions.
SEP IRA contributions can be made after the tax year ends. The deadline is the due date of your federal income tax return for that year, including extensions.8Internal Revenue Service. Retirement Plans: FAQs Regarding SEPs For sole proprietors filing Form 1040, that’s April 15. If you file Form 4868 for an automatic extension, the deadline stretches to October 15.9Internal Revenue Service. Get an Extension to File Your Tax Return You can even establish a new SEP IRA by that extended deadline and fund it for the prior year.
That extension is genuinely useful. It gives you time to close the books on self-employment income, calculate the exact contribution, and decide how much shelter you actually want. The contribution is deducted on Schedule 1 of Form 1040, reducing your adjusted gross income.5Internal Revenue Service. Self-Employed Individuals: Calculating Your Own Retirement Plan Contribution and Deduction
Penalties for Going Over
Contribute more than the allowed amount to your SEP IRA and the IRS imposes a 6% excise tax on the excess for every year it stays in the account.10Office of the Law Revision Counsel. 26 USC 4973 – Tax on Excess Contributions to Certain Tax-Favored Accounts and Annuities The tax compounds annually until you withdraw or correct the excess. You report and pay it on Form 5329.
Overcontributions on the 401(k) side work differently. Excess elective deferrals above $24,500 get included in taxable income for the year. If the plan doesn’t distribute the excess by April 15 of the following year, you can end up taxed on the same money twice, once at contribution and again at distribution.
For plan-level mistakes like exceeding the annual additions limit, the IRS Employee Plans Compliance Resolution System (EPCRS) provides a path to fix errors without disqualifying the plan. Small errors caught quickly can be self-corrected; larger or systemic problems may need a formal submission through the Voluntary Correction Program.11Internal Revenue Service. EPCRS Overview A disqualified plan loses its tax-favored status retroactively, which is the outcome you’re trying to avoid.
Is a Solo 401(k) a Better Fit Than a SEP IRA?
If your reason for wanting a SEP IRA is that you have self-employment income alongside a W-2 job, a solo 401(k) is worth comparing. Both plans share the same $72,000 annual additions limit, but the solo 401(k) lets you contribute as both employee and employer.
The catch for someone already covered by a W-2 401(k): the $24,500 elective deferral limit is shared across all 401(k) plans, so you can’t defer $24,500 at work and another $24,500 into a solo 401(k). The employer profit-sharing side of the solo 401(k) still gives you room, at roughly 20% of net self-employment earnings, the same rate that governs a SEP IRA. Where the solo 401(k) pulls ahead is when the W-2 job doesn’t already consume your elective deferral. If your net self-employment earnings are $60,000 and you have deferral room left, a SEP IRA maxes out around $12,000 while a solo 401(k) lets you defer up to $24,500 as employee plus roughly $12,000 as employer, for about $36,500 total.
Solo 401(k) plans also allow Roth elective deferrals, plan loans in many cases, and catch-up contributions. The tradeoff is administrative complexity. A solo 401(k) requires a written plan document, and once plan assets exceed $250,000 you file Form 5500-EZ annually.12Internal Revenue Service. 2025 Instructions for Form 5500-EZ SEP IRAs have almost no ongoing paperwork.