Yes — as long as your spouse also earns compensation from your business, they can be a second participant in the same Solo 401(k) alongside you. It’s still treated as a “one-participant” plan for IRS purposes, so you keep the simplified paperwork, and each spouse gets their own full contribution limit based on their own earnings — not a shared household limit.
Why a spouse doesn’t turn your Solo 401(k) into something more complicated
The IRS defines a one-participant 401(k) as “a traditional 401(k) plan covering a business owner with no employees, or that person and his or her spouse,” according to the IRS page on one-participant 401(k) plans. A business owner with no other common-law employees doesn’t need to run nondiscrimination testing on the plan — and that stays true even with a participating spouse, since the whole point of the exception is that a spouse isn’t treated as a disqualifying “other employee.”
The IRS’s own annual reporting form makes the same point in its title: Form 5500-EZ is the “Annual Return of A One-Participant (Owners/Partners and Their Spouses) Retirement Plan.” A spouse is baked into the definition, not an exception to it.
The requirement that actually matters: your spouse needs their own earned income
A 401(k) contribution — whether it’s an elective deferral or an employer/profit-sharing contribution — is always based on compensation. No compensation, no contribution base. So the real question isn’t whether your spouse is allowed to participate; it’s whether they actually have earnings from the business to base a contribution on.
There are two common ways to make that true — and which one applies changes how your spouse’s contribution is actually calculated:
- Your spouse is a W-2 employee of the business. They’re paid a wage, and that wage is their compensation for plan purposes.
- You and your spouse run the business as a qualified joint venture. If you materially participate together and file a joint return, you can elect to split a jointly run business into two separate Schedule Cs — one for each of you — so your spouse has their own net self-employment earnings, reported and taxed as their own, per the Schedule SE instructions.
If your spouse is a W-2 employee of the business
Your spouse’s side of the plan is figured the way any employee’s would be — not through the self-employed reduced-rate calculation. The plan can make an employer/nonelective contribution of up to 25% of your spouse’s actual W-2 compensation, per the IRS page on one-participant 401(k) plans, which lists “25% of compensation as defined by the plan” as the employer contribution limit for anyone who isn’t self-employed — no adjustment for self-employment tax, since a W-2 employee doesn’t pay it. On top of that, your spouse can also elect to defer part of their own wage as an employee contribution.
Because this doesn’t run through the self-employment math, our Self-Employed Retirement Contribution Calculator — built around net self-employment profit — doesn’t apply to this side of the plan. You’d figure it directly: 25% of their W-2 wage, capped by the plan’s overall annual-additions limit.
If your spouse is a co-owner (qualified joint venture)
Here, your spouse has their own net self-employment earnings, calculated the same way yours are — so their contribution does go through the same self-employed reduced-rate calculation, and you can use the calculator for each of you separately. If you split the business 50/50 as a qualified joint venture and total net profit is $90,000, for example, each of you would report your own $45,000 share on a separate Schedule C and run that $45,000 through the calculator individually.
Either way, the deferral limit is per person — and shared with any other job
Whichever path applies, the elective deferral piece works the same way for both of you: $24,500 for 2026 plus catch-up if eligible, per person, per IR-2025-111 — not split between you as a household. And if your spouse also has a 401(k) or 403(b) at another job, that limit is shared with it the same way it would be for you — see Can I Have a Solo 401(k) and a 401(k) at Work? for exactly how that works.
A quick example
Say your sole proprietorship’s revenue minus expenses would be $90,000 for the year if you paid your spouse nothing. Paying your spouse doesn’t just move $30,000 out of that figure — it triggers three separate, real deductions on your own Schedule C, per the Instructions for Schedule C:
- The $30,000 wage itself (Line 26).
- Your employer share of Social Security and Medicare tax on that wage — 7.65%, or about $2,295 (Line 23; this is the employer’s matching share, separate from what’s withheld from your spouse’s paycheck).
- The employer/nonelective contribution you make to the plan on your spouse’s behalf — the $7,500 from above (Line 19). This is specifically for contributions made for employees; your own contribution as the self-employed owner goes on Schedule 1, not here.
That’s $90,000 − $30,000 − $2,295 − $7,500 ≈ $50,200 — not $60,000 — as your own Schedule C net profit. That’s what your own Solo 401(k) contribution is based on; run roughly $50,200 through the calculator to see your number.
Your spouse’s side isn’t calculated from that $50,200 at all — it’s the $7,500 employer contribution (25% of their $30,000 wage) plus whatever they separately elect to defer as their own employee contribution. Paying your spouse doesn’t just create a second pot of money inside the same plan; between the wage, the matching payroll tax, and their retirement contribution, it’s a real reduction to your own contribution base too.
Bottom line
A spouse who genuinely works in and earns from your business can join your Solo 401(k) without turning it into a more complicated plan. The thing to get right is making sure your spouse actually has compensation from the business — informal help with no pay doesn’t create a contribution base, no matter how much they’re involved.