Self-employment means no company retirement plan handed to you, so you build your own. Two accounts dominate the choice, and picking the right one can shape decades of savings.
Two Accounts Built for People Without an Employer Plan
A Solo 401(k), sometimes called a one-participant or individual 401(k), is a full 401(k) plan designed for a business that has no employees other than the owner and, if applicable, a spouse. It gives self-employed people the same structure a large company offers its staff, minus the corporate overhead. Sole proprietors, single-member LLCs, partnerships, and S-corps can all sponsor one.
A SEP IRA (Simplified Employee Pension) is exactly what its name suggests: a stripped-down retirement plan funded entirely through employer contributions. There is no employee salary deferral and almost no ongoing maintenance. You open it much like a regular IRA and fund it from the business side.
Both are tax-advantaged, both let your investments grow without annual taxation on gains, and both are meant for people whose income does not come with a workplace 401(k). The differences show up in how much you can put away, how the money is taxed, and how much paperwork you take on. Treat the numbers here as an educational framework, not personalized tax advice for your specific return.
The Contribution Math Is Where They Split
The headline advantage of a Solo 401(k) is that you contribute in two roles: as the employee and as the employer. For 2025, the employee deferral is up to $23,500, and on top of that you can add an employer profit-sharing contribution of up to 25% of compensation. Combined, the two roles can reach $70,000 before any catch-up contributions.
A SEP IRA only allows the employer piece. Contributions are capped at 25% of compensation, up to that same $70,000 ceiling for 2025, with no separate employee deferral and no catch-up provision. Because it lacks the flat employee contribution, a SEP IRA usually requires substantially higher income to reach the same total.
Consider a sole proprietor with $60,000 of net self-employment income. In a Solo 401(k), that person could set aside the full employee deferral plus a percentage-based employer contribution, often landing north of $30,000. In a SEP IRA at the same income, only the employer contribution applies, so the total is closer to $11,000 or $12,000. At lower and moderate incomes, the employee deferral is the decisive edge.
The gap narrows at high incomes, where both plans can hit the ceiling. Savers age 50 and older can add a catch-up contribution to a Solo 401(k) that a SEP IRA does not offer, and recent rules created an even larger catch-up for a narrow age band in the early 60s. These figures are indexed and change most years, so confirm the current limits before you fund an account.
Roth Options and How Withdrawals Are Taxed
Traditional contributions to either plan are made pre-tax, lowering your taxable income now, with income tax due when you withdraw in retirement. That upfront deduction is often the main appeal for self-employed savers managing an unpredictable tax bill.
Where they diverge is the Roth option. Many Solo 401(k) plans allow Roth contributions, letting you pay tax now so qualified withdrawals later come out tax-free. A traditional SEP IRA historically offered no Roth version, though recent legislation opened the door to Roth SEP contributions where a provider supports them, and availability still varies widely.
The Roth-versus-traditional decision hinges on whether you expect your tax rate to be higher now or in retirement, which is genuinely hard to predict. Younger savers or those in a temporary low-income year sometimes favor Roth; established earners in a high bracket often prefer the immediate deduction. Because this interacts with your other income, deductions, and state taxes, it is a good example of a choice worth reviewing with a qualified tax professional.
Both accounts also share familiar back-end rules: required minimum distributions eventually apply to traditional balances, and early withdrawals before age 59½ generally trigger taxes and a penalty. Neither is meant to be a short-term savings vehicle.
Paperwork, Deadlines, and Ongoing Upkeep
Simplicity is the SEP IRA’s strongest selling point. You can open one with a short form, there is generally no annual government filing, and you decide each year how much, if anything, to contribute. That flexibility suits businesses with lumpy or seasonal income, since you are never locked into a fixed deferral.
A Solo 401(k) carries more structure. It requires a formal plan document, and once total plan assets exceed a threshold (currently $250,000), the IRS expects an annual information return. The trade-off for that extra administration is the higher contribution capacity, plus Roth and loan features that a SEP lacks.
Deadlines differ too. A SEP IRA can typically be established and funded up to your business’s tax-filing deadline, including extensions, which helps if you are deciding in the spring how much to shelter from the prior year. A Solo 401(k) generally must be established by the end of the tax year to make employee deferrals for it, even though some employer contributions can be added later.
One structural limit matters for growing businesses: both plans assume you have no eligible employees beyond an owner and spouse. Hire full-time staff who meet the eligibility rules, and a Solo 401(k) no longer fits, while a SEP would require you to contribute the same percentage for those employees.
Matching the Account to Your Situation
For many solo earners with modest or moderate income, the Solo 401(k) wins on raw contribution room because the employee deferral does not depend on a percentage of profit. Someone earning $50,000 to $80,000 who wants to save aggressively can usually shelter far more in a Solo 401(k) than a SEP would allow at the same income.
The SEP IRA earns its keep on simplicity and timing. If you value being able to open and fund an account after year-end with a single form, dislike paperwork, or have income that swings from year to year, the SEP’s low-maintenance design is a real advantage. High earners who consistently max out either plan may find the practical difference smaller than expected.
These are also not mutually exclusive with every other option. Depending on income, a self-employed person might pair either plan with a traditional or Roth IRA, and business structure, sole proprietor versus S-corp, changes how the contribution math actually works out. Those interactions are exactly where general guidance stops being enough.
The right call comes down to how much you want to contribute, whether Roth access matters to you, and how much administrative simplicity is worth. Because the limits are indexed annually and the rules carry real tax consequences, use this as a starting point and confirm the specifics for your own circumstances before opening an account.
