Novak Financial Partners · April 2026
The Solo 401(k) Guide for 1099 Earners
2026 Edition
What's the best retirement plan for a 1099 earner? For most self-employed high earners, a Solo 401(k) beats a SEP IRA on every measure that matters: higher contributions at lower income, Roth access, and compatibility with the backdoor Roth IRA.
If you're self-employed, a contractor, or earning 1099 income on the side, you already know the tax bill is brutal. A Solo 401(k) is one of the most powerful retirement plans available to anyone, and most 1099 earners either don't have one or are using a SEP IRA when they shouldn't be.
For most of our clients, the optimal approach is to max pre-tax contributions first (employee and employer) and contribute the remainder as after-tax with mega backdoor Roth conversions. That combination delivers both an immediate tax deduction and tax-free growth in the same plan, in the same year.
This guide covers why a Solo 401(k) beats a SEP IRA, how the mega backdoor Roth works inside it, and what to watch for when choosing a provider.
Key takeaways
- Solo 401(k) reaches the $72,000 limit at lower income than a SEP IRA (~$190,000 vs. ~$288,000)
- The best-of-both-worlds strategy: max pre-tax first, then add after-tax and mega backdoor Roth on top
- SEP IRA balances trigger the pro-rata rule, which makes backdoor Roth IRA conversions not worth doing. Solo 401(k) balances do not.
- Most off-the-shelf Solo 401(k) plans don't support after-tax contributions. You need a specialized provider.
Why a Solo 401(k) beats a SEP IRA for most 1099 earners
Both plans have the same $72,000 total contribution limit in 2026. But that's where the similarity ends. The Solo 401(k) wins on four fronts that matter for most self-employed high earners.
| Feature | Solo 401(k) | SEP IRA |
|---|---|---|
| 2026 contribution limit | $72,000 | $72,000 |
| Income needed to max out | ~$190,000 | ~$288,000 |
| Employee contribution | Up to $24,500 | Not allowed |
| Employer contribution | Up to 25% of comp | Up to 25% of comp |
| Roth contributions | Yes | No |
| Mega backdoor Roth | Yes (with right provider) | No |
| Backdoor Roth IRA compatible | Yes | No (pro-rata rule) |
| Catch-up for age 50+ | +$8,000 | None |
| Participant loans | Up to $50,000 | Not allowed |
| Allows employees | No (spouse only) | Yes |
1. Reach higher contributions at lower income.
A SEP IRA is funded only from the employer side, capped at 25% of compensation. To hit $72,000, you'd need roughly $288,000 in self-employment income. A Solo 401(k) lets you contribute as both employee and employer. You can put in $24,500 as the employee before any employer math starts, so you can max out with closer to $190,000 in income. That's roughly $98,000 less income needed to hit the same limit.
2. Access Roth contributions and the mega backdoor.
SEP IRAs are pre-tax only. No Roth option, no after-tax contributions, no mega backdoor. A Solo 401(k) allows Roth contributions on the employee side, and with the right provider, it allows after-tax contributions with in-plan Roth conversions. This is the mega backdoor, and it's the single biggest difference between the two plans for anyone who wants meaningful Roth exposure.
3. Keep the backdoor Roth IRA usable.
This is the one most people miss. The backdoor Roth IRA (a non-deductible traditional IRA contribution followed by a Roth conversion) is subject to the pro-rata rule, which considers all of your pre-tax IRA balances when calculating how much of a conversion is taxable. SEP IRA balances count. The more you contribute to a SEP IRA, the more of each backdoor Roth conversion becomes taxable, often making the strategy not worth doing. Solo 401(k) balances do not count toward the pro-rata rule, which keeps your backdoor Roth IRA fully usable. For high earners who want to keep stacking Roth every way possible, this matters.
4. Borrow from the plan if needed.
Solo 401(k)s allow loans of up to 50% of the account value, capped at $50,000. SEP IRAs do not allow loans at all. For most people, this doesn't come up. But if you ever need short-term liquidity, it's useful optionality.
When a SEP IRA still makes sense: if you have employees beyond a spouse, or if you want the simplest possible setup and don't care about Roth access, a SEP IRA may be easier. For most solo 1099 earners, though, the Solo 401(k) is the stronger tool.
How the mega backdoor Roth works inside a Solo 401(k)
A Solo 401(k) has three contribution buckets:
Employee contribution: Up to $24,500 in 2026 ($32,500 if age 50+). Can be pre-tax or Roth.
Employer contribution: Up to 25% of compensation (around 20% for sole proprietors). Pre-tax only.
After-tax contribution: Fills whatever's left between the first two buckets and the overall $72,000 limit. This is the bucket that unlocks the mega backdoor.
The after-tax bucket on its own is not that attractive. You contribute with after-tax dollars, and any growth is taxable. But the mega backdoor fixes that by converting the after-tax contribution to Roth immediately, before any growth happens. Once converted, the money grows tax-free and comes out tax-free in retirement.
The best-of-both-worlds strategy
For most of our clients, the optimal approach is to max pre-tax first and contribute the remainder to Roth via after-tax contributions and in-plan conversions:
Step 1: Max pre-tax first. Contribute $24,500 as pre-tax employee deferrals, plus the full employer contribution. At a 32% federal marginal bracket, this produces roughly $7,840 in immediate federal tax savings on the employee portion alone, plus more on the employer side. That deduction is real money back in your pocket this year.
Step 2: Contribute the remainder to Roth. Fill the remaining space up to the $72,000 cap with after-tax contributions, then immediately convert to Roth. This part grows tax-free and comes out tax-free in retirement.
The result: an immediate tax deduction on the pre-tax portion and tax-free growth on the Roth portion, inside the same plan, in the same year.
A worked example. Say you earn $200,000 in net self-employment income in 2026 as a sole proprietor:
| Employee contribution (pre-tax) | $24,500 |
| Employer contribution, ~20% as sole proprietor (pre-tax) | $40,000 |
| Pre-tax subtotal (deductible this year) | $64,500 |
| After-tax contribution, converted to Roth | $7,500 |
| Total contributed | $72,000 |
A pre-tax deduction of roughly $20,000 to $25,000 in combined federal and state tax savings this year, plus $7,500 of tax-free Roth growth compounding for decades. At a SEP IRA, the same $200,000 income would max out at $40,000, all pre-tax, with no Roth component at all.
How to set it up correctly
This is where most people get stuck. The mega backdoor Roth is not available at most free or off-the-shelf Solo 401(k) providers. To make it work, your plan must allow three specific features:
1. After-tax contributions beyond the standard pre-tax and Roth employee contributions.
2. In-plan Roth conversions or in-service distributions to a Roth IRA.
3. Enough income to make contributions beyond the employee + employer limit.
Most brokerage-based Solo 401(k)s (Fidelity, Schwab, Vanguard, E*TRADE) do not allow after-tax contributions or in-plan conversions. They're designed for simple setups, which means no mega backdoor.
Specialized Solo 401(k) providers like My Solo 401k Financial, Carry, and Employee Fiduciary offer plans that support the mega backdoor. They charge setup and annual administration fees, typically in the $300 to $1,500 range, which is modest relative to the tax savings.
The key steps:
1. Open a Solo 401(k) with a provider that supports after-tax contributions and in-plan conversions.
2. Make your employee and employer contributions first.
3. Calculate remaining room up to the $72,000 cap. Contribute that as after-tax.
4. Convert the after-tax contribution to Roth immediately, before it earns any growth. Any gains that accrue before conversion are taxable.
Common mistakes
Using a SEP IRA when a Solo 401(k) would be better. SEP IRAs get set up first because they're simpler, but most 1099 earners are giving up Roth access and higher contributions at lower income. The Solo 401(k) is usually the better long-term choice.
Assuming every Solo 401(k) supports the mega backdoor. Most don't. The big-name brokerage plans are free and simple, but they strip out after-tax contributions and in-plan conversions. You need a specialized provider for the mega backdoor to work.
Waiting to convert after-tax contributions. Any gains in the after-tax bucket before conversion are taxable as ordinary income. Convert immediately, same day if possible.
Ignoring it because you also have W-2 income. If you earn 1099 income on the side, you can still open a Solo 401(k) for that business. Your employee contribution limit is shared across all 401(k)s, but the employer and after-tax buckets are separate. There may be room to contribute even if your W-2 401(k) is maxed.
Frequently asked questions
What is the mega backdoor Roth Solo 401(k)?
A strategy that lets self-employed individuals contribute after-tax dollars to a Solo 401(k) and immediately convert them to Roth. Combined with pre-tax employee and employer contributions, total annual contributions can reach $72,000 in 2026. Most clients use it to layer a Roth bucket on top of their pre-tax contributions, capturing both an immediate tax deduction and tax-free Roth growth. It requires a Solo 401(k) that supports after-tax contributions and in-plan Roth conversions.
Is a Solo 401(k) better than a SEP IRA for 1099 earners?
For most self-employed individuals without employees, yes. A Solo 401(k) reaches the $72,000 limit with about $190,000 in income versus $288,000 for a SEP IRA. It also allows Roth contributions and the mega backdoor Roth, which a SEP IRA does not. SEP IRAs may still be simpler for businesses with multiple employees.
Should I make pre-tax or Roth contributions in my Solo 401(k)?
For most high earners, the optimal approach is to max pre-tax contributions first (employee and employer) to capture the immediate tax deduction, and contribute the remainder as after-tax with mega backdoor Roth conversions. This gives you both a current-year deduction on the pre-tax portion and tax-free growth on the Roth portion.
Does a SEP IRA affect the backdoor Roth IRA?
Yes, and not in a good way. SEP IRA balances count toward the pro-rata rule, which is used to calculate how much of a backdoor Roth conversion is taxable. The more you have in a SEP IRA, the more of each backdoor Roth conversion becomes taxable, often making the strategy not worth doing. Solo 401(k) balances do not count toward the pro-rata rule, which keeps the backdoor Roth IRA fully usable.
Can I contribute to both a Solo 401(k) and a SEP IRA in the same year?
Usually not for the same business. Both plans count toward the same $72,000 overall limit. If you run two separate businesses that are not treated as a controlled group, you may be able to maintain both. Confirm with a qualified tax professional.
Can I have a Solo 401(k) if I also have a W-2 job with a 401(k)?
Yes. If you earn 1099 income on the side, you can open a Solo 401(k) for that business. The $24,500 employee contribution limit is shared across all 401(k)s, but the employer and after-tax buckets are separate. Many people with maxed W-2 401(k)s can still contribute meaningfully on the employer and after-tax side of a Solo 401(k).
Which Solo 401(k) providers support the mega backdoor Roth?
Most large brokerages (Fidelity, Schwab, Vanguard, E*TRADE) do not support after-tax contributions or in-plan Roth conversions. Specialized providers like My Solo 401k Financial, Carry, and Employee Fiduciary do, typically for a setup fee and annual administration cost in the $300 to $1,500 range.
What is the deadline to open a Solo 401(k) for 2026?
You must establish the plan by December 31, 2026 to make employee contributions for 2026. Employer contributions can be made up to your business tax filing deadline (including extensions). SEP IRAs can be opened and funded up to the tax deadline, which is one reason they are sometimes set up last-minute.
How much income do I need to fully max out a Solo 401(k)?
To reach the $72,000 limit using only employee and employer contributions, you need roughly $190,000 in net self-employment income. With the mega backdoor Roth, after-tax contributions can fill any gap below that, so you can effectively max out at lower income levels.
The bottom line
For 1099 earners who want to maximize tax-advantaged savings, a Solo 401(k) with the mega backdoor Roth feature is one of the most powerful tools available. Used well, it lets you move up to $72,000 per year into tax-advantaged accounts: some of it pre-tax for the immediate deduction, the rest in Roth for tax-free growth. A SEP IRA at the same income might get you a third of that amount, all pre-tax, with no Roth component and the additional drawback of blocking clean backdoor Roth IRA contributions.
The catch is setup. The wrong provider makes the strategy impossible. The right one makes it automatic.
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Schedule your intro callThis document is for educational and informational purposes only and does not constitute personalized investment, tax, legal, or financial planning advice. Contribution limits, tax rates, and rules referenced are based on 2026 IRS guidance and are subject to change. Solo 401(k) eligibility, mega backdoor Roth strategy, and contribution math depend on individual business structure, income, and plan design. Third-party providers are mentioned for informational purposes only and are not endorsements. Consult a qualified financial, tax, or legal professional before implementing any strategy. Advisory services are offered through Core Planning LLC, a Registered Investment Advisor. For additional disclosures please visit corepln.com/disclosures.