One-participant 401(k) plan is sometimes called a:
Solo 401(k)
Solo-k
Uni-k
One-participant k
The one-participant 401(k) plan isn't a new type of 401(k) plan. It's a traditional 401(k) plan covering a business owner with no employees, or that person and his or her spouse. These plans have the same rules and requirements as any other 401(k) plan.
Contribution limits in a one-participant 401(k) plan
The business owner wears two hats in a 401(k) plan: employee and employer. Contributions can be made to the plan in both capacities. The owner can contribute both:
Elective deferrals up to 100% of compensation (“earned income” in the case of a self-employed individual) up to the annual contribution limit:
$19,000 in 2018, or $25,000 in 2018 if age 50 or over; plus
Employer nonelective contributions up to:
25% of compensation as defined by the plan, or
for self-employed individuals, see discussion below
Example 100k salary - $19,000 elective deferral PLUS 20% employer contribution on net adjusted earnings (Self employed)
If you’ve exceeded the limit for elective deferrals in your 401(k) plan, find out how to correct this mistake.
Total contributions to a participant’s account, not counting catch-up contributions for those age 50 and over, cannot exceed ($55,000 for 2018; $56,000 for 2019).
Example: Ben, age 51, earned $50,000 in W-2 wages from his S Corporation in 2018. He deferred $19,000 in regular elective deferrals plus $6,000 in catch-up contributions to the 401(k) plan. His business contributed 25% of his compensation to the plan, $12,500. Total contributions to the plan for 2018 were $37,000. This is the maximum that can be contributed to the plan for Ben for 2018.
A business owner who is also employed by a second company and participating in its 401(k) plan should bear in mind that his limits on elective deferrals are by person, not by plan. He must consider the limit for all elective deferrals he makes during a year.
Contribution limits for self-employed individuals
You must make a special computation to figure the maximum amount of elective deferrals and non-elective contributions you can make for yourself. When figuring the contribution, compensation is your “earned income,” which is defined as net earnings from self-employment after deducting both:
one-half of your self-employment tax, and
contributions for yourself.
Use the rate table or worksheets in Chapter 5 of IRS Publication 560, “Retirement Plans for Small Business,” for figuring your allowable contribution rate and tax deduction for your 401(k) plan contributions. See also Calculating Your Own Retirement Plan Contribution.
401k Limits/Profit Sharing Plan -
Two annual limits apply to contributions:
A limit on employee elective deferrals; and
An overall limit on contributions to a participant’s plan account (including the total of all employer contributions, employee elective deferrals (but not catch-up contributions) and any forfeiture allocations).
Deferral limits for 401(k) plans
The limit on employee elective deferrals (for traditional and safe harbor plans) is:
$19,000 in 2019
The $19,000 amount may be increased in future years for cost-of-living adjustments
Generally, you aggregate all elective deferrals you made to all plans in which you participate to determine if you have exceeded these limits. If a plan participant’s elective deferrals are more than the annual limit, find out how you can correct this plan mistake.
After tax rollovers - https://www.irs.gov/retirement-plans/rollovers-of-after-tax-contributions-in-retirement-plans