The Solo 401(k) for S-Corp Owners: 2026 Limits and Deadlines
August 17, 2026
A solo 401(k) can shelter far more than a SEP or IRA, up to $72,000 in 2026. Here is how it works for S-Corp owners and why year-end timing matters.
If you run a business with no employees other than yourself, and maybe a spouse, there is a retirement account built for your exact situation that can often shelter more than a SEP-IRA or a traditional IRA, especially at lower and moderate income. It is called a solo 401(k), also known as a one-participant 401(k), and most owners who qualify for one either do not have it or are not using it to its full potential.
Here is how it works, what it can do for 2026, and why the calendar matters more than most people realize.
Why a Solo 401(k) Can Beat a SEP or a Traditional IRA
The reason a solo 401(k) is so powerful is that it lets you contribute in two capacities at once: as the employee and as the employer. A SEP-IRA only allows the employer piece, and a traditional IRA is capped far lower. A SEP and a solo 401(k) top out at the same overall limit for the year, but the solo 401(k) often reaches that ceiling at a much lower income, because the employee deferral stacks on top of the employer contribution.
You wear both hats. As the employee, you make a salary deferral. As the employer, your business makes a profit-sharing contribution on top of it. For a profitable year, that combination can move a meaningful amount of income either off this year's tax bill or into decades of tax-advantaged growth.
The 2026 Numbers
For 2026, the pieces work like this:
Employee deferral: up to $24,500, with an extra $8,000 if you are 50 or older, or $11,250 if you are age 60 to 63 during the year.
Employer contribution: up to 25% of compensation. For an S-corp owner, that means 25% of your W-2 wages. For a sole proprietor or partner, it is based on a special earned-income calculation that works out to less than a flat 25% of business profit.
Combined limit: up to $72,000 for the year, before any catch-up.
A Roth option is often available. Many solo 401(k) plans let you make the employee deferral as Roth, so you can choose whether that money is sheltered now or set up to grow tax-free for later. Which one is right depends on your bracket today versus the one you expect in retirement.
The Part That Makes This a Fall Decision, Not a December One
This is where owners lose money to the calendar without realizing it.
Timing is the catch, and it depends on your entity. If your business is taxed as an S-corp, your employee deferrals run through payroll, so the plan needs to be in place and the deferrals flowing before year-end. Waiting until the final weeks of December leaves almost no room to actually get the money in, because there are not enough remaining paychecks to run the deferrals through. Sole proprietors with no employees generally have more room, since the rules let an owner-only business adopt a plan after year-end, up to the tax filing deadline. But if you pay yourself a W-2 wage through an S-corp, the payroll clock is real.
Set the plan up now, while there is still runway, and the rest of the year quietly does the work.
Is a Solo 401(k) Right for You?
The fit is cleanest for a profitable solo business with no non-spouse employees. If you have had a strong year and no plan in place, it is one of the more reliable wins available to an owner, and the window to use it fully for 2026 is open right now. As with any retirement plan decision, the exact numbers depend on your entity type, your compensation, and your broader plan, so it is worth confirming the specifics for your situation.
Frequently Asked Questions
How much can I contribute to a solo 401(k) in 2026? Up to $72,000 combined for the year before catch-up contributions: as much as $24,500 as an employee deferral, plus an employer contribution of up to 25% of compensation. For a sole proprietor or partner, that employer piece runs off a special earned-income calculation and lands below a flat 25%. Owners who are 50 or older can add $8,000, and those age 60 to 63 can add $11,250.
Can an S-corp owner have a solo 401(k)? Yes. For an S-corp owner, the employer contribution is based on your W-2 wages, and employee deferrals are made through payroll. The plan generally must be established by December 31 to count for that year.
What is the deadline to set up a solo 401(k)? For an S-corp, the plan generally needs to be in place before year-end for this year's employee deferrals, since those run through payroll, and because deferrals depend on remaining paychecks, setting it up in the fall rather than late December matters. Sole proprietors with no employees generally have more flexibility, since the rules allow adopting an owner-only 401(k) after year-end, up to the tax filing deadline.
Solo 401(k) versus SEP-IRA: which allows a larger contribution? Both top out at the same overall limit for the year, $72,000 before catch-up. The difference is that a solo 401(k) often reaches that ceiling at a lower income, because it adds an employee salary deferral on top of the employer contribution that a SEP-IRA offers on its own. The right answer depends on your income and entity type.
Is there a Roth version of a solo 401(k)? Many solo 401(k) plans offer a Roth option for the employee deferral, depending on how the plan is designed. That lets you choose tax-free growth later instead of a deduction now.
Where This Leaves You
A solo 401(k) is one of the largest, simplest levers a solo owner has, and it is quietly time-sensitive. The contribution room is generous, the Roth flexibility is useful, and the only real enemy is the calendar. The decision belongs on the fall to-do list, not the year-end scramble, because by the time December arrives most of the opportunity has already run out through the payroll you did not adjust.
If something here hits close to home, get in touch. Reader questions are what shaped this issue in the first place.
This article was adapted from The Kindled Brief, a monthly newsletter on keeping more of what you earn.
Written by Kindled Planning: Light the way to your financial future.
A CPA-led personal CFO service helping equity compensation earners and entrepreneurs make confident, tax-smart financial decisions.
