SEP IRA 2026: Contribution Limits, the 20% Rule, and When It Beats a Solo 401(k)

A SEP IRA is the simplest high-contribution retirement account for self-employed owners. You can contribute up to $72,000 for 2026, and you have until October 15 to fund it — even if you decide in September. Here's what it costs you compared to a solo 401(k), and when each is the right call.

What is a SEP IRA?

A Simplified Employee Pension (SEP) IRA is an employer-funded retirement account that lets a business owner make deductible contributions to an IRA set up for each eligible employee — including themselves. For a solo self-employed person, "each eligible employee" is just you, so setup is as simple as opening an IRA at any major custodian and filing IRS Form 5305-SEP. There are no annual plan documents, no 5500-EZ filing requirement, and no December 31 deadline to worry about.

Why sole proprietors effectively use a 20% rate

The IRS formula looks circular at first: the SEP contribution reduces your net self-employment income, which is the base the contribution is calculated on. To cut through the math, the IRS provides a simplified rate: for self-employed owners, the contribution rate is 20% of net self-employment income (net profit before the SEP deduction).¹ This is algebraically equivalent to applying the nominal 25% rate to income after the SE tax deduction — just simpler to calculate.

For S-corp owner-employees, the rate remains 25% of your W-2 salary from the corporation, because the SE deduction issue doesn't apply to W-2 income.

2026 contribution by income level

Solo 401(k) figures: $24,500 employee deferral + 20% employer profit-sharing (sole-prop rate), capped at $72,000 total per IRC §415(c), 2026. SEP IRA has no catch-up; solo 401(k) allows $8,000 catch-up (ages 50–59, 64+) or $11,250 super catch-up (ages 60–63), increasing the solo 401(k) advantage further for those age groups.

The key takeaway: the solo 401(k) advantage is exactly the employee deferral amount ($24,500) at nearly every income level, because the employer contribution rates are the same. That gap only narrows above ~$300K as both plans approach their common $72,000 ceiling. Below $360K, the solo 401(k) lets you shelter materially more income.

The deadline advantage: SEP IRA's biggest selling point

A solo 401(k) requires you to elect your deferral amount by December 31 — in writing — before you even know what your year-end income will be. Miss that deadline and you lose the employee deferral portion for that year entirely. A SEP IRA has no such deadline: contributions can be made all the way to your tax-filing deadline including extensions, which is October 15, 2027 for the 2026 tax year for most filers.

This matters most for owners with genuinely unpredictable income. A consultant whose $400K engagement lands in November might not know final net income until March. A SEP IRA lets them wait until September and still fund the full $72,000.

When SEP IRA wins over a solo 401(k)

• You have W-2 employees. A solo 401(k) requires no full-time non-owner employees. The moment you hire someone full-time, you must offer the same SEP contribution rate to them. A SEP IRA handles this uniformly by design — same rate, applied to all eligible employees' compensation.
• Income is above ~$360K and you value simplicity. Both plans max at $72,000. If you don't need the catch-up contribution room and you'd rather skip the December 31 election paperwork, the SEP IRA delivers the same limit with less friction.
• You're in a volatile year. Irregular income owners benefit most from the SEP's October deadline. See the full analysis in the Irregular Income Retirement Calculator.
• You're starting mid-year. A SEP IRA can be opened and funded retroactively for the prior tax year, any time before the filing deadline. No year-end plan adoption required.

The pro-rata trap: SEP IRA and backdoor Roth

If your income exceeds the Roth IRA phase-out threshold ($165,000 single / $246,000 MFJ in 2026²), you can't contribute directly to a Roth IRA. The workaround — a backdoor Roth IRA — involves making a non-deductible traditional IRA contribution and converting it to Roth. But the IRS's pro-rata rule aggregates all your traditional IRA balances, including your SEP IRA, when calculating how much of the conversion is taxable.

Example: you have $180,000 in a SEP IRA and make a $7,000 non-deductible traditional IRA contribution. When you convert the $7,000, only 3.7% of it ($7K / $187K) is tax-free. You'll owe tax on 96.3% of the conversion. The SEP IRA makes the backdoor Roth almost useless.

A solo 401(k) solves this: qualified plans are not subject to the pro-rata rule, and a solo 401(k) can absorb your SEP IRA balance via rollover — clearing the deck for clean backdoor Roth contributions going forward.

Employee coverage rules

If you have employees, you must cover all employees who are at least 21 years old, earned at least $800 in 2026 from your business, and worked for you in at least 3 of the last 5 years.³ You must contribute the same percentage of compensation for every covered employee as you contribute for yourself. At a 20% SEP contribution rate and multiple employees, this can add significant cost — another reason to run the numbers before committing to the plan type.

Setting up a SEP IRA

Setup takes 15 minutes. You have two options:

1. IRS Form 5305-SEP (free): a standard prototype plan document the IRS provides. Sign it, keep a copy, open an IRA at any major custodian, and you're done. You don't file 5305-SEP with the IRS — it's just your internal plan document.
2. Custodian prototype plan: Fidelity, Schwab, Vanguard, and others offer their own prototype SEP IRA agreements that accomplish the same thing. Functionally identical to 5305-SEP for most solo operators.

Unlike the solo 401(k), SEP IRA accounts are funded directly into each participant's IRA account at the custodian — there is no plan trust account, no IRS 5500-EZ filing, and no year-end compliance checklist.