SEP-IRA vs. SIMPLE vs. Solo 401(k): Choosing a Retirement Plan for Your Business

A retirement plan is one of the few tools that lets a business owner cut this year's tax bill and build long-term wealth at the same time. The catch: there are several plans, and the "best" one depends entirely on your income, whether you have employees, and how much paperwork you're willing to run.

Here's a plain-English comparison of the three plans most small businesses actually use — the SEP-IRA, the SIMPLE IRA, and the Solo 401(k) — and how to think about which fits.

SEP-IRA — the simplest big deduction

A SEP-IRA (Simplified Employee Pension) is the easiest plan to open and the one many self-employed owners start with. The business contributes up to 25% of compensation (about 20% of net self-employment income for a sole proprietor), up to a generous annual dollar cap that adjusts each year.

• Best for: self-employed owners and businesses with few or no employees who want a large, flexible deduction with almost no administration.
• Watch out: contributions must be the same percentage for every eligible employee. If you have staff, funding your own account also means funding theirs — which gets expensive fast.
• Admin: minimal. No annual government filing.

SIMPLE IRA — built for small teams

A SIMPLE IRA (Savings Incentive Match Plan for Employees) is designed for businesses with up to 100 employees. Employees defer part of their salary, and the employer either matches up to 3% of pay or contributes a flat 2% for everyone.

• Best for: established small businesses with employees that want to offer a retirement benefit without the cost and complexity of a full 401(k).
• Watch out: contribution limits are lower than a SEP or Solo 401(k), so it's less powerful for a high-earning owner trying to maximize their own deferral.
• Admin: low, but the employer contribution is mandatory each year.

Solo 401(k) — the maximizer for owner-only businesses

A Solo 401(k) (also called an Individual or One-Participant 401(k)) is for a business with no employees other than the owner and a spouse. It's powerful because you contribute in two capacities: as the employee (a salary deferral) and as the employer (a profit-sharing contribution of up to 25%). Stacked together, this usually allows a larger total contribution than a SEP at the same income — especially at moderate income levels.

• Best for: owner-only businesses (and owner + spouse) who want to contribute the maximum.
• Bonuses: many Solo 401(k)s allow a Roth option and loans, which SEPs and SIMPLEs generally don't.
• Watch out: once you hire a non-spouse employee, you generally can't keep it as a Solo plan. Once assets exceed a threshold, a simple annual information return is required.

Quick decision guide

• Just you (or you + spouse), want the maximum? → Solo 401(k).
• Just you, want the absolute simplest large deduction? → SEP-IRA.
• You have employees and want a low-cost team benefit? → SIMPLE IRA (or step up to a traditional 401(k) as you grow).

The tax math that makes this worth doing

Every dollar you contribute to a traditional version of these plans is generally deducted from taxable income now. For an owner in a combined 30–40% federal-and-state bracket, a five-figure contribution can translate into thousands of dollars of tax saved this year — while the money grows tax-deferred until retirement. That is the rare win-win in the tax code: pay yourself first and pay the IRS less.

Deadlines matter

Timing rules differ by plan — a SEP can often be established and funded up until your extended tax-filing deadline, while a SIMPLE and the salary-deferral portion of a Solo 401(k) generally must be set up earlier. Missing the window means losing the deduction for the year, so this is a conversation to have before year-end, not at filing time.

Contribution limits and rules change annually and depend on your specific facts. This is general information, not tax advice — confirm the current-year numbers and deadlines with your CPA.