How MUCH of 1099 Income Can I Put in SOLO 401k?

Watch: How much of your 1099 income you can really contribute to a Solo 401k — and how the Mega Backdoor Roth fits in.

If you receive income reported on Form 1099-NEC, a Solo 401k can be one of the most powerful ways to save for retirement and reduce your current-year taxable income. But how much of that 1099 income can actually go into the plan isn’t a simple fixed percentage — it depends on your net self-employment income, how your business is taxed, whether you also contribute to another employer plan, your age, and which contribution types your Solo 401k plan allows.

What Counts as 1099 Income for Solo 401k Purposes?

Your gross Form 1099-NEC amount is only the starting point — it is not the figure used to calculate your Solo 401k contribution. As a sole proprietor, that income flows onto Schedule C, where business expenses are deducted first.

Step	What Happens
1. Start with gross 1099-NEC income	This is reported income from clients — not your final contribution base.
2. Report on Schedule C	Deduct business expenses to arrive at net self-employment income.
3. Identify Line 31	This is your net profit figure — the starting point for all Solo 401k contribution calculations.
4. Subtract ½ of self-employment tax	The resulting figure is what’s actually used to calculate employee, employer, and voluntary after-tax contributions.

Warning: A common misconception is calculating Solo 401k contributions directly off the gross 1099-NEC amount. My Solo 401k Financial stresses that you must first move that income to Schedule C, subtract expenses and one-half of self-employment tax, and use that final figure — not the gross 1099 number.

Info Highlight: The Solo 401k contribution calculator from My Solo 401k Financial performs this calculation for you — just plug in Line 31 of your Schedule C, and it will subtract one-half of self-employment tax automatically.

Employee, Employer, and Voluntary After-Tax Contributions

A Solo 401k plan offered by My Solo 401k Financial is drafted for maximum flexibility, allowing employee salary deferrals, employer profit sharing contributions, and voluntary after-tax contributions — whether pre-tax or Roth.

Contribution Type	2026 Limit / Calculation
Employee salary deferral	Up to $24,500 (dollar-for-dollar)
Employer profit sharing (sole proprietorship)	20% of net self-employment income (after Line 31 minus ½ SE tax)
Voluntary after-tax	Remaining room up to the $72,000 overall limit

Example: You can also choose to skip employee and employer contributions entirely and make the full $72,000 overall limit as a single voluntary after-tax contribution, then convert it to the Roth Solo 401k using the Mega Backdoor Roth strategy — as long as your net self-employment income supports it.

What If I Also Have a Daytime Job 401k?

Many 1099 contractors also hold a full-time job with its own employer 401k. Whether your Solo 401k contributions are limited by that daytime plan depends on the contribution type.

Contribution Type	Aggregated With Day-Job 401k?
Employee salary deferral	Yes — shared $24,500 limit across both plans
Employer profit sharing	No — calculated separately from net self-employment income
Voluntary after-tax (Mega Backdoor Roth)	No — calculated separately from net self-employment income

Example: You max out your $72,000 daytime employer 401k. As long as your 1099 side business has enough net self-employment income, you can still make a full $72,000 voluntary after-tax contribution to your Solo 401k and convert it to the Roth Solo 401k or Roth IRA — supercharging your total retirement savings across both plans.

2026 Catch-Up Contribution Rules

Age Range	2026 Catch-Up Amount
50–59, and 64+	$8,000 (normal catch-up)
60–63 (SECURE 2.0 super catch-up)	$11,250 (in place of the normal catch-up)

Important: Catch-up and super catch-up contributions can never be made as voluntary after-tax contributions. For a sole proprietorship, they can be made as either pre-tax or Roth Solo 401k contributions. Starting in 2026, a mandatory Roth catch-up rule under SECURE 2.0 requires higher-earning S-corp and C-corp owners to make catch-up contributions as Roth — but this rule does not apply to 1099-NEC contractors, sole proprietorships, or partnerships.

Is Your LLC Actually a Self-Employed Business?

Example: A couple asked whether their Solo 401k’s profit-and-loss allocation in a family-owned LLC holding rental real estate needs to match their capital contribution percentage. The more fundamental question comes first: is the LLC actually a self-employed business, or just a passive investment entity? Simply forming an LLC doesn’t make you self-employed — what matters is whether you’re performing material services (doing the actual work) and reporting it as earned income, rather than investment, passive, or distribution income.

Info Highlight: Solo 401k eligibility and contributions are based on true self-employment activity — earned income from work performed — not on rental income, capital gains, or other passive or investment income.

Common Mistakes to Avoid

Mistake	Why It’s Wrong
Using gross 1099-NEC income to calculate contributions	You must use net self-employment income from Schedule C, Line 31, minus ½ self-employment tax.
Contributing without earned income	No earned income from self-employment activity means no contributions of any type — employee, employer, or voluntary after-tax.
Assuming employer profit sharing contributions don’t need earned income	Even though these are deducted on the business return, they still require sufficient earned income to justify them.
Assuming every Solo 401k plan allows the Mega Backdoor Roth	Not all providers allow voluntary after-tax contributions — confirm your plan supports it before relying on the strategy.

The Mega Backdoor Roth Solo 401k in Action

My Solo 401k Financial was the first provider in the industry to offer the Mega Backdoor Roth strategy for Solo 401k plans, going back to 2013. For a one-participant plan — say, a 1099-NEC contractor operating as a sole proprietorship — the plan is sponsored by the self-employed business itself, with three separate holding accounts (often at Fidelity or Schwab) for pre-tax, Roth, and voluntary after-tax funds. It’s one plan, not three.

Steps to Complete the Mega Backdoor Roth

Example: Contribute to the voluntary after-tax holding account, then convert those funds to the Roth Solo 401k (or Roth IRA) holding account. My Solo 401k Financial reports the conversion to the IRS via Form 1099-R once the online conversion form is timely submitted through the Forms tab. For a two-participant plan — such as spouses both self-employed in the same S-corp — each spouse maintains separate holding accounts and can independently perform the Mega Backdoor Roth strategy, each receiving their own Form 1099-R.

Ready to Maximize Your 1099 Income in a Solo 401k?
Whether you want to calculate your exact contribution limit, run the Mega Backdoor Roth strategy, or figure out if your side business truly qualifies, our team can help you set up the right Solo 401k structure.

Next Steps:
Get Started Today — or watch more videos and read more posts from My Solo 401k Financial to learn how to grow your retirement account tax-efficiently.

Remember: This information is provided for educational purposes only. Always consult with qualified tax, legal, and investment professionals before making investment decisions with your retirement funds.