The Scenario
Devon’s consulting income jumped this year, and his accountant says he is leaving thousands of dollars in tax savings on the table by not having a retirement plan. Devon opens a browser and finds SEP IRA and Solo 401(k) compared in a hundred forum threads with no clear winner.
The winner depends on his situation, and the good news is that the choice comes down to three questions.
Who This Guide Is For
This is for self-employed people and business owners without employees: freelancers, consultants, and side hustlers with meaningful income. If you have employees, check the rules carefully, because both plans carry obligations that change with a team.
What to Look For
Compare the two plans on:
- Contribution limits. How much you can save per year.
- Flexibility. Roth options, loans, and catch-up contributions.
- Paperwork. Opening and ongoing maintenance burden.
- Employee rules. What happens when you hire.
SEP IRA
The SEP IRA is the simple plan. You, as the employer, contribute up to a percentage of each participant’s compensation, with the annual limit set by the IRS. There is minimal paperwork, and you can open and fund it after the year ends, up to the tax filing deadline.
The tradeoffs: contributions come only from the employer side, there is no Roth option, no catch-up contributions, and if you hire staff, you generally must contribute for eligible employees at the same rate.
Solo 401(k)
The Solo 401(k) is built for owner-only businesses. You can contribute as an employee (a salary deferral, with Roth available in many plans) plus as an employer, which pushes the total limit higher. Older owners get catch-up contributions, and some plans allow loans.
The tradeoffs: more setup, plan document requirements, and the December 31 deadline to establish the plan for the current year.
How to Choose
Choose a SEP IRA if you want the simplest possible plan, if you may open it after year-end, or if you prefer the provider’s lowest-friction option.
Choose a Solo 401(k) if you want maximum contributions, Roth savings, or catch-up room, and you are comfortable with slightly more paperwork.
If you plan to hire employees soon, ask a professional before choosing; the Solo 401(k)‘s employee rules are stricter in some ways.
Contribution Math: A Worked Example
Imagine you clear $80,000 of self-employment income. A SEP IRA lets your business contribute up to roughly 20 percent of net profit as a tax deduction. A Solo 401(k) adds an employee salary-deferral layer on top of that employer contribution, so the same income can support a noticeably larger total - and if you are 50 or older, catch-up contributions push it further.
The practical difference: the Solo 401(k) converts more of your income into tax-deferred savings each year, which is why owners with meaningful income often pick it despite the extra paperwork. If your income is modest, the simpler SEP still delivers the core benefit: a deductible contribution that also grows tax-deferred.
What Happens When You Hire
Both plans change when employees arrive. A SEP IRA generally requires contributions for eligible employees at the same percentage you fund for yourself. A Solo 401(k) is designed for owner-only businesses, so hiring staff usually means the plan needs updating or replacing. If you expect to hire within a year or two, run the “with employees” numbers before you commit, because the plan that looked ideal solo can become expensive with a team.
Signs You Are Ready to Open One
You are ready when three things are true: your income is steady enough to fund a contribution, you have the cash-flow cushion to spare the money, and you already know which low-cost provider you will use. If those are not true yet, keep the money in savings and revisit the decision at your next quarterly review - opening the account is the easy part; funding it consistently is the plan. And read the provider’s fee schedule before you open, even when a plan is advertised as free; administrative costs vary and small balances feel them first.
What Not to Overpay For
Do not pay a financial advisor a percentage of assets just to open a plan you can set up yourself at a low-cost brokerage. Do not choose a plan with high administrative fees because of marketing.
And do not let the plan choice delay saving entirely. The best plan is the one you fund.
What to Buy
Vanguard and Fidelity both offer low-cost SEP IRAs and individual 401(k)s with straightforward setup and index-fund options. If you want an automated approach with professional management, Betterment offers retirement accounts with hands-off investing.
Pick the plan that fits, set an automatic contribution, and let the tax savings and compound growth do the rest.