Estimate employee and employer solo 401(k) contribution limits for owner-only businesses.
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A Solo 401(k), also called an Individual 401(k) or one-participant 401(k), is the most powerful retirement savings vehicle available to self-employed individuals with no employees (other than a spouse). It combines employee elective deferrals with employer profit-sharing contributions to allow significantly higher total contributions than a SEP IRA or traditional IRA.
Unlike a SEP IRA (which only allows employer contributions), a Solo 401(k) lets you contribute in two capacities. As the employee, you can defer up to $23,000 (or $30,500 if age 50+) of your earned income. As the employer, you can add up to 25% of your net self-employment income after the SE tax deduction. These two contributions stack, often allowing you to shelter $40,000-$69,000 or more per year.
The Solo 401(k) advantage is most dramatic at lower income levels. If you earn $60,000, a SEP IRA limits you to about $11,000 (25% of adjusted income). A Solo 401(k) allows $23,000 in employee deferrals plus $11,000 in employer contributions, totaling $34,000 -- more than triple the SEP. At very high incomes (above $280,000+), the two plans converge near the same limit.
Many Solo 401(k) providers offer a Roth option for the employee deferral portion. This lets you make after-tax contributions that grow and are withdrawn completely tax-free in retirement. SEP IRAs do not offer a Roth option at all. This makes the Solo 401(k) uniquely flexible for tax planning.