Solo 401(k) vs. SEP IRA: Which Retirement Plan Fits Your Business?

The short comparison

A SEP IRA takes employer contributions only and is easy to open. A solo 401(k) allows both employee and employer contributions but is for owners with no employees other than a spouse.

Here is a side-by-side overview. Contribution limits change yearly, so we describe the structure instead of quoting dollar amounts. Check IRS.gov for current figures.

The right choice depends on your income, your staff and how much you want to save.

How a SEP IRA works

A SEP IRA lets the business contribute a percentage of compensation to an IRA for the owner and any eligible employees. The same percentage applies to everyone.

With a SEP IRA, only the employer makes contributions. As a sole proprietor, you are both employer and owner. Contributions are tax-deductible to the business within IRS limits, and you can decide each year how much to put in, or whether to skip a year.

The big drawback is that if you have eligible employees, you must contribute the same percentage for them as for yourself. A one-person shop does not face this issue, but a growing business might.

Opening one is quick. Most major brokerages offer a form you can complete in minutes. You can often fund it up to your tax filing deadline, but confirm the date with your accountant.

How a solo 401(k) works

A solo 401(k) lets you contribute as both employee and employer, which often allows higher savings when income is modest. It is limited to owners without other employees.

As the employee, you defer part of your pay. As the employer, you add a profit-sharing contribution. Combined, these can let a lower-income owner save more than a SEP IRA would permit, because the employee deferral does not depend on a percentage of profit in the same way.

Added features may include a Roth option and plan loans, depending on the provider. Those features make the plan flexible, but you must follow the plan rules, and the plan must usually be established by a deadline for the tax year in question.

Once plan assets pass a threshold set by the IRS, you may need to file an annual information return. Ask your provider or accountant about current rules.

Which is better at different income levels

At lower profit, a solo 401(k) often allows more saving. At high profit, both plans can reach similar maximums, so simplicity may decide.

Here is an illustrative example of why structure matters. Suppose Owner A has modest net profit and wants to save as much as possible. The solo 401(k)'s employee deferral lets Owner A set aside a larger share of income than a SEP IRA's percentage-based formula would. Owner B has high profit. Both plans may reach similar totals, so the easier SEP IRA may be enough.

If you expect to hire employees, a SEP IRA could become costly because you must match their contribution percentage. A solo 401(k) is not permitted once you hire eligible employees, so you would need to switch plans. Plan for where your business will be in two or three years.

Setup, deadlines and taxes

Set up the plan with a brokerage, record contributions in your books, and confirm deadlines with your accountant. Contributions are generally deducted on your personal return for self-employed owners.

Steps for either plan:

1. Choose a provider with low fees and the features you want.
2. Open the plan and keep the plan documents.
3. Decide on the annual contribution after you know profit.
4. Make the contribution and keep a record.
5. Report it correctly with your tax preparer.

Deadlines vary by plan type and entity, so do not rely on memory. A sole proprietor, an S corporation owner and a partnership partner may calculate compensation differently. Ask your accountant, and review tax write-offs for the self-employed and single-member LLCs taxed as S corporations for related context.

Retirement saving and business cash flow

Retirement contributions reduce cash available to run the business. Set the amount after you cover taxes, operating costs and your reserve.

A flexible plan matters because income for self-employed owners is uneven. Both plans let you decide the amount each year, so you can save more in a strong year and less when cash is tight. Make sure you are not funding retirement by delaying payroll taxes or running up expensive short-term debt.

Priorities usually run in this order: pay taxes, fund operating costs, build a cash reserve, then make retirement contributions. See our guide to paying yourself from a single-member LLC for help setting a steady draw.

When the business needs capital instead

Do not pull from retirement accounts to fund the business without advice. Early withdrawals may bring taxes and penalties, and financing can be a better tool when payback is clear.

Raiding retirement money to fund a business can cost more than it looks like. Early distributions may be taxed and penalized, and you lose years of growth. Talk to a tax professional before considering it.

If your business has a clear use for capital, such as equipment that will add revenue, outside financing may fit better. ROI Funder considers businesses with 6+ months in business, $20,000+ monthly revenue and 500+ FICO. Options include equipment financing and working capital, with true cost and payback shown up front.