Yes, you can have both a Solo 401(k) and a Roth IRA, and contributing to one has no effect on how much you can put into the other. The IRS treats them as separate accounts with independent limits. For 2026, a self-employed business owner under 50 could set aside up to $79,500 across the two accounts, and considerably more with catch-up contributions. The only real friction comes from the Roth IRA’s income limits, which the Solo 401(k) does not share.
Who Can Open Each Account
The Solo 401(k) is built for self-employed people with no full-time employees other than a spouse. The IRS calls it a “one-participant 401(k) plan,” and it works for sole proprietors, single-member LLCs, S-corps, and partnerships alike.1Internal Revenue Service. One Participant 401k Plans Hire someone who works more than 1,000 hours in a year and you lose eligibility, at which point you would need to move to a standard 401(k) with its testing requirements.
Roth IRA eligibility rests on two things: you need earned income (wages, salary, or self-employment earnings), and your modified adjusted gross income has to fall below certain thresholds. Passive income such as dividends, rent, or interest does not count as earned income for this purpose.
2026 Contribution Limits for Both Accounts
The Solo 401(k) has two contribution buckets that stack. The employee elective deferral is capped at $24,500 for 2026. The employer profit-sharing piece can go up to 25% of your W-2 compensation if your business pays you a salary, or roughly 20% of net self-employment earnings for sole proprietors. Combined, the two buckets cannot exceed $72,000.2Internal Revenue Service. Retirement Topics – 401(k) and Profit-Sharing Plan Contribution Limits
Catch-up contributions push the ceiling higher if you are 50 or older. The standard 2026 catch-up is $8,000, raising the total to $80,000. A SECURE 2.0 provision creates a higher catch-up tier for people who turn 60, 61, 62, or 63 during the year: $11,250 in 2026, taking the maximum to $83,250.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
The Roth IRA runs on a separate track entirely. For 2026, the limit is $7,500 under 50, or $8,600 at 50 and older thanks to the newly indexed $1,100 catch-up.4Internal Revenue Service. Retirement Topics – IRA Contribution Limits Maxing the Solo 401(k) does not shrink your Roth IRA limit by a dollar. A business owner under 50 who fills both accounts saves $79,500 in a year. Someone aged 60 through 63 could reach $91,850.
Roth IRA Income Phaseouts
The Solo 401(k) has no income ceiling. You could earn $2 million and still contribute the full amount. The Roth IRA works differently. Your ability to contribute directly phases out once your modified adjusted gross income (MAGI) crosses certain thresholds. For 2026:3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
- Single or head of household: full contributions below $153,000 MAGI, reduced contributions between $153,000 and $168,000, none above $168,000.
- Married filing jointly: full contributions below $242,000, reduced between $242,000 and $252,000, none above $252,000.
- Married filing separately: the phaseout runs from $0 to $10,000, which cuts off direct contributions for anyone in this filing status with meaningful income.
If your MAGI lands inside the phaseout range, the IRS reduces your allowable contribution proportionally. Cross the top of the range and direct contributions stop entirely. That does not mean Roth savings are off the table.
The Backdoor Roth When You Earn Too Much
Business owners priced out of a direct Roth IRA contribution commonly use the backdoor Roth. Two steps: contribute to a traditional IRA on a nondeductible basis (no tax break on the deposit), then convert those funds to a Roth IRA. Federal tax law imposes no waiting period between the two.
File Form 8606 with your tax return in any year you make nondeductible traditional IRA contributions or convert to a Roth. The form records your cost basis so the same dollars are not taxed twice at conversion.5Internal Revenue Service. Instructions for Form 8606 Skipping it triggers a $50 penalty and, more consequentially, can leave you paying tax again on money you already paid tax on if the IRS has no record of your basis during a future audit.
The pro-rata rule is what trips people up. When you convert, the IRS looks at the total balance across all your traditional, SEP, and SIMPLE IRAs and calculates what share is pre-tax versus after-tax. Say you have $95,000 of pre-tax money in a rollover IRA and you contribute $7,500 nondeductible. Only about 7% of the conversion comes out tax-free; the rest is taxed as ordinary income.
This is where holding a Solo 401(k) genuinely helps. You can roll pre-tax traditional IRA balances into the Solo 401(k), zeroing out the pre-tax IRA figure the IRS uses in its pro-rata calculation. With no pre-tax IRA money in view, the backdoor conversion is essentially tax-free. People who leave old IRA balances in place get an unpleasant surprise at tax time.
The Mega Backdoor Roth
Some Solo 401(k) plans support a larger Roth conversion strategy. If the plan document allows voluntary after-tax contributions (distinct from Roth elective deferrals) and in-plan conversions, you can put after-tax dollars in above the $24,500 elective deferral limit, up to the $72,000 overall 415(c) ceiling, and convert them to the plan’s Roth account. Earnings between contribution and conversion are taxable; the contributed principal is not. This can move tens of thousands of extra dollars into Roth status each year, but only if your plan document is written to permit it.
Roth Options Inside the Solo 401(k) Itself
Beyond the separate Roth IRA, your Solo 401(k) plan document can include a designated Roth account. You direct some or all of your $24,500 employee elective deferrals into the Roth bucket within the 401(k), where the money grows tax-free.6Office of the Law Revision Counsel. 26 USC 402A – Optional Treatment of Elective Deferrals as Roth Contributions The important difference from a Roth IRA: no income phaseouts. An owner earning $500,000 can still put the full $24,500 into the plan’s Roth side.
Employer profit-sharing contributions used to be pre-tax only, but the SECURE 2.0 Act changed that. Plans can now allow matching and nonelective contributions to be designated as Roth.7Internal Revenue Service. SECURE 2.0 Act Impacts How Businesses Complete Forms W-2 If your plan document is updated for this feature, the entire $72,000 annual addition could go to Roth. The tradeoff is that Roth employer contributions are included in your taxable income for the year, which can be a heavy upfront tax bill. Most owners mix pre-tax and Roth based on their current bracket and expected future rates.
Contribution Deadlines
The Solo 401(k) has split deadlines. Employee elective deferrals require a written election by December 31 of the tax year, so you have to decide how much of your compensation you are deferring before the year closes. Employer profit-sharing contributions can be made up to your business’s tax filing deadline, including extensions. For most sole proprietors and single-member LLCs, that stretches as late as October 15 of the following year with an extension.
Roth IRA contributions follow the personal return deadline, meaning April 15, 2027 for 2026 contributions (adjusted if the date lands on a weekend or holiday). Extending your tax return does not extend the Roth IRA contribution deadline.
Watch-Outs Before You Fund Both Accounts
Two Roth five-year clocks run independently. Your Roth IRA’s clock starts on January 1 of the first tax year you make any Roth IRA contribution, and once five years have passed and you reach 59½ (or qualify through disability or a first-time home purchase), both contributions and earnings come out tax-free.8Internal Revenue Service. Publication 590-B, Distributions from Individual Retirement Arrangements (IRAs) A designated Roth account inside a 401(k) has its own separate five-year clock, measured from the first Roth contribution to that specific plan. A 15-year-old Roth IRA does nothing for a designated Roth account you just opened.9Internal Revenue Service. Roth Account in Your Retirement Plan Rolling the designated Roth 401(k) balance into a Roth IRA later can let you piggyback on the Roth IRA’s older clock if it has already cleared five years.
Over-contributing to a Roth IRA triggers a 6% excise tax on the excess for every year it stays in the account.4Internal Revenue Service. Retirement Topics – IRA Contribution Limits You can avoid the penalty by pulling out the excess and any earnings on it before your tax filing deadline, including extensions. Miss that window and the 6% keeps compounding until you fix it. Solo 401(k) excess elective deferrals must be distributed by April 15 of the following year to avoid double taxation. Employer contributions that push past the $72,000 Section 415(c) ceiling require correction through the IRS’s programs, and the employer may owe a 10% excise tax on the excess.10Internal Revenue Service. Fixing Common Plan Mistakes – Failure to Limit Contributions for a Participant
One coordination trap catches business owners who also participate in another employer’s 401(k) alongside their Solo 401(k). The $24,500 elective deferral cap applies across all 401(k) plans combined, not per plan. Tracking that aggregate is entirely the participant’s responsibility, and over-deferring across multiple plans is one of the most common errors the IRS sees in this area.