SEP IRA vs. Solo 401(k): Which Saves You More in Taxes?

For most self-employed business owners with no employees, a Solo 401(k) usually allows a larger tax-deductible contribution at the same income level than a SEP IRA, because it adds an employee salary-deferral piece on top of the employer contribution. But the SEP IRA is simpler to run and can make more sense if you have eligible employees. Comparing what a Solo 401(k) and a SEP IRA each let a self-employed owner deduct, rather than which is simpler to run, is the first step in choosing the plan that keeps more of what you earn.

This is a decision business owners get wrong all the time, not because the rules are hidden, but because nobody looks at the plan choice as part of a coordinated strategy. The right answer depends on whether you have employees, how much you want to contribute, and how the plan fits alongside your income, taxes, and long-term retirement picture.

How do SEP IRA and Solo 401(k) plans actually work?

Both are retirement plans built for self-employed people and small business owners. Both let you make pre-tax contributions that lower your taxable income for the year. The difference is in how contributions are structured and who the plan has to cover.

SEP IRA

A Simplified Employee Pension. The business makes contributions on behalf of the owner (and any eligible employees). Contributions come only from the employer side. There is no employee salary-deferral piece.

Solo 401(k)

A 401(k) for a business with no full-time employees other than the owner and a spouse. It has two parts: an employee salary deferral and an employer profit-sharing contribution. Also called an individual 401(k) or one-participant 401(k).

Net self-employment earnings

Your business profit after expenses, adjusted for the deductible portion of self-employment tax. This is the number your contribution limits are calculated from, not gross revenue.

The plan choice isn't about which name sounds better. It's about which structure lets you contribute more, cover the right people, and fit your broader tax picture.

What are the SEP IRA contribution limits for business owners?

A SEP IRA contribution is calculated as a percentage of your net self-employment earnings, up to an annual dollar cap set by the IRS. For 2024, the total employer contribution to a SEP IRA is capped at 25% of eligible compensation, up to an IRS-set dollar limit that adjusts each year. Because self-employed owners calculate against net earnings rather than a W-2 salary, the effective rate works out lower than a flat 25% once self-employment tax is factored in.

The key point for business owners: SEP IRA contribution limits are entirely employer-driven. There is no separate deferral you can add as an individual. So your contribution is tied directly to your business profit.

If you have eligible employees, a SEP IRA generally requires you to contribute the same percentage of pay for them as you do for yourself. That can turn a personal tax move into a meaningful payroll cost, which is exactly the kind of downstream consequence proactive planning is meant to catch before you sign the paperwork.

Why does a Solo 401(k) usually allow a bigger contribution?

The Solo 401(k) stacks two contributions on top of each other:

• Employee salary deferral: You can defer up to the annual IRS elective deferral limit, plus a catch-up amount if you are age 50 or older.
• Employer profit-sharing: On top of the deferral, the business can contribute up to 25% of eligible compensation.

Because the deferral portion is a flat dollar amount rather than a percentage, a Solo 401(k) lets you reach the total contribution ceiling at a lower income level than a SEP IRA. At modest income, that difference can be substantial. At very high income, both plans approach the same overall dollar cap set by the IRS.

The trade-off: a Solo 401(k) only works if you have no full-time employees other than yourself and a spouse. The moment you hire eligible full-time staff, the Solo 401(k) generally no longer qualifies, and you'd need a different plan structure.

SEP IRA vs. Solo 401(k): side-by-side comparison

If you have no employees and want to maximize contributions, the Solo 401(k) is often the stronger tool. If you have staff or want the simplest possible plan, the SEP IRA earns its place.

Which plan saves more in taxes for a self-employed owner?

Both plans reduce your taxable income by the amount you contribute, so a larger contribution generally means a larger deduction. That's why the Solo 401(k) frequently wins on pure tax reduction for solo owners: it lets you contribute more at the same profit level.

But "which saves more in taxes" is the wrong question to ask in isolation. The contribution deduction is only one lever. The real question is how the plan fits alongside your entity structure, your other income, a possible business sale, and your retirement income plan. A plan that maximizes this year's deduction but ignores your five-year picture may leave money on the table elsewhere.

This is the gap between tax filing and tax strategy. Your CPA files the return and reports what happened. Proactive tax planning looks forward and coordinates the moving parts. If you want to understand that distinction more deeply, see our breakdown of tax compliance vs. tax strategy.

What should business owners consider before choosing?

A few questions tend to settle the decision:

• Do you have employees? If yes, the Solo 401(k) is generally off the table, and a SEP IRA means matching contributions for eligible staff. Other plan types may fit better.
• How much do you want to contribute? If you want to push toward the maximum at a modest income, the Solo 401(k)'s deferral piece helps.
• Do you want Roth or loan features? A Solo 401(k) often offers both; a SEP IRA generally does not.
• How much administrative work can you take on? A SEP IRA is close to set-and-forget. A Solo 401(k) requires more attention once it grows.
• Are you planning a business sale or exit? Retirement plan structures can play a role in reducing tax exposure during a liquidity event. See our guide to tax-efficient business exit planning.

The plan you pick today also shapes your future retirement income. Pre-tax contributions grow tax-deferred, which means the tax bill arrives later, when you take distributions. Building a plan without thinking about how those distributions will be taxed later is a common blind spot, one we cover in how to reduce taxes on IRA distributions and 401(k) withdrawals.

The best plan on paper is the one that fits your whole financial picture, not just this April's return.

Where does coordinated planning fit in?

Choosing between a SEP IRA and a Solo 401(k) is a single decision inside a much larger system. On its own, it's a good move. Coordinated with your entity structure, your tax strategy, your retirement income plan, and your eventual exit, it becomes far more powerful. That coordination is what most business owners never get, because their CPA, financial advisor, and attorney rarely talk to each other.

At Anchor, we operate as a fiduciary under the Investment Advisers Act, a distinct standard from the best interest obligation under Reg BI that applies at all times across the advisory relationship rather than only when a recommendation is made, and our role is to strategize and coordinate, not to file your return or draft your documents. You keep your CPA and your attorney. We connect the pieces so that a retirement plan decision like this one supports every other part of your financial life instead of working against it.

Frequently asked questions

Can I have both a SEP IRA and a Solo 401(k)?

In some situations, yes, but combined contributions are limited by IRS rules and the two plans interact in ways that require careful coordination. Most owners choose one. Talk to a qualified tax professional before running both.

What happens to my Solo 401(k) if I hire an employee?

A Solo 401(k) generally only works with no full-time employees other than a spouse. Once you hire eligible full-time staff, you'd typically need to convert to a different plan structure that covers employees. Plan for this before you hire.

How are SEP IRA contribution limits calculated for a self-employed owner?

They're based on a percentage of your net self-employment earnings (your business profit after expenses and the deductible portion of self-employment tax), up to an annual dollar cap set by the IRS. It is not calculated on gross revenue.

Does a SEP IRA require me to contribute for my employees?

Generally, yes. A SEP IRA typically requires the same contribution percentage for all eligible employees as you contribute for yourself. That can make it a meaningful payroll cost if you have staff.

Which plan is better for reducing my taxes this year?

For a solo owner with no employees, a Solo 401(k) often allows a larger deductible contribution at the same income, which can mean a larger deduction. But the best choice depends on your full financial picture, not just this year's return. Results depend on individual circumstances and current law.

Are these contributions tax-free forever?

No. Pre-tax contributions defer the tax: they grow tax-deferred, and you pay tax when you take distributions in retirement. Coordinating how those future distributions are taxed is an important part of the plan.

Sources

1. IRS, Simplified Employee Pension (SEP) Plans. SEP IRA structure, contribution rules, and employee coverage requirements.
2. IRS, One-Participant 401(k) Plans. Solo 401(k) contribution structure, deferral plus profit-sharing, and eligibility.
3. IRS, Retirement Topics: Contributions. Annual contribution and deferral limits and how they adjust.
4. IRS, Retirement Plans for Self-Employed People. Overview of plan options and net earnings calculations.