How LLC Owners Save on Taxes in 2026

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Tax Strategy • §401(k) / §402(g)

Mega Backdoor Roth

Contribute up to $46,500 in after-tax dollars to your 401(k) and convert to Roth — tax-free growth for high earners blocked from direct Roth contributions.

$46,500Max after-tax 401(k) add-on (2026)

The Mega Backdoor Roth is an advanced retirement strategy available inside certain 401(k) plans that allows high-income earners to contribute after-tax dollars beyond the standard $23,500 elective deferral limit, then convert those dollars to Roth — creating a pool of tax-free retirement assets that is not subject to income limits or the standard Roth IRA contribution cap of $7,000. The strategy is especially powerful for S-Corp owners, tech employees, and high-income professionals who are phased out of direct Roth IRA contributions.

How the Mega Backdoor Roth Works

The 2026 §415(c) total annual additions limit for a 401(k) is $70,000 ($77,500 if age 50+). This limit encompasses three components:

Component2026 LimitTax Treatment
Employee elective deferrals (pre-tax or Roth)$23,500Pre-tax or Roth
Employer match / profit sharingUp to plan limitPre-tax
After-tax voluntary contributions (Mega Backdoor)Up to $46,500 remaining roomAfter-tax — converted to Roth

The strategy requires two plan features: (1) the plan must allow after-tax voluntary contributions beyond the elective deferral limit, and (2) the plan must allow in-service distributions or in-plan Roth conversions (also called in-plan Roth rollovers under §402A(c)(4)). Without both features, the strategy is unavailable.

S-Corp Owner Advantage

S-Corp owners who sponsor their own 401(k) plan can design the plan to allow both after-tax contributions and in-plan Roth conversions. A solo 401(k) with Mega Backdoor Roth capability allows an owner-employee to:

Contribution TypeAmountNotes
Employee elective deferral (Roth)$23,500After-tax, grows tax-free
Employer profit sharing (pre-tax)25% of W-2 wagesDeductible to the S-Corp
After-tax voluntary (Mega Backdoor)Remaining §415(c) roomConverted to Roth immediately

Example: S-Corp owner with $150,000 W-2 salary. Elective deferral: $23,500 (Roth). Employer profit sharing: $37,500 (25% × $150K). Remaining §415(c) room: $70,000 − $23,500 − $37,500 = $9,000 Mega Backdoor Roth. Total Roth-equivalent contributions: $32,500/year.

Income Limits and Eligibility

Unlike direct Roth IRA contributions, the Mega Backdoor Roth has no income limit. It is available to any participant whose 401(k) plan allows after-tax contributions and in-service conversions, regardless of AGI. This makes it the primary Roth accumulation vehicle for high earners above the $165,000 (single) / $246,000 (MFJ) Roth IRA phase-out range in 2026.

Pro-rata rule does not apply. Unlike the standard Backdoor Roth IRA (which is affected by the pro-rata rule if you have pre-tax IRA balances), the Mega Backdoor Roth operates entirely within the 401(k) plan and is not subject to the IRA aggregation rules of §408(d)(2).

Tax Treatment of the Conversion

After-tax contributions to a 401(k) have a cost basis equal to the amount contributed. When converted to Roth via an in-plan Roth conversion, only the earnings on the after-tax contributions are taxable — not the principal. If the conversion is done promptly (same day or within days of the contribution), earnings are minimal and the tax cost is negligible. This is why the strategy is sometimes called the “in-plan Backdoor Roth.”

Converted amounts are reported on Form 1099-R with distribution code G (direct rollover) or H (direct rollover to Roth). The taxable portion (earnings only) is included in gross income in the year of conversion.

Plan Design Requirements

Not all 401(k) plans support the Mega Backdoor Roth. Key plan design requirements:

RequirementDetails
After-tax voluntary contributionsPlan must explicitly allow after-tax contributions beyond the elective deferral limit
In-plan Roth conversion or in-service distributionPlan must allow either in-plan Roth rollovers (§402A(c)(4)) or in-service distributions to a Roth IRA
ACP nondiscrimination testingAfter-tax contributions are subject to ACP testing — solo plans (one participant) are exempt
Plan document amendmentThird-party administrator (TPA) must amend plan document to include these features

Solo 401(k) plans (owner-only or owner + spouse) are exempt from ACP and ADP nondiscrimination testing, making them the simplest vehicle for implementing the Mega Backdoor Roth.

Frequently Asked Questions

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More Tax Planning FAQs

What is the S-Corp election and how does it reduce self-employment tax?
An S-Corp election allows the owner to split income between a reasonable salary (subject to 15.3% FICA) and distributions (not subject to FICA). For a business owner with $200,000 in net profit paying an $80,000 salary, the annual SE tax savings are approximately $15,500–$18,500. The S-Corp must file Form 2553 within 75 days of formation.
What is the Section 199A QBI deduction and how does it apply?
The §199A deduction allows pass-through business owners to deduct up to 23% of qualified business income (QBI) from taxable income under OBBBA. For taxpayers above $403,500 (MFJ) in 2026, the deduction is limited to the greater of 50% of W-2 wages or 25% of W-2 wages plus 2.5% of qualified property.
What retirement plan options are available for self-employed professionals?
Self-employed professionals can establish a Solo 401(k) (up to $70,000 in 2026), a SEP-IRA (25% of net self-employment income up to $70,000), a SIMPLE IRA ($16,500 + $3,500 catch-up), or a Defined Benefit Plan (up to $280,000+ depending on age). The Solo 401(k) is the best option for most self-employed professionals.
How does the home office deduction work for self-employed professionals?
Self-employed professionals who use a dedicated home office space exclusively and regularly for business qualify for the home office deduction under §280A. The deduction is calculated as a percentage of home expenses equal to the office square footage divided by total home square footage. The simplified method allows $5/sq ft up to 300 sq ft ($1,500 maximum).
What vehicle deductions are available for self-employed professionals?
Self-employed professionals can deduct vehicle expenses using either the standard mileage rate (70 cents/mile in 2026) or actual expenses. Vehicles with a GVWR over 6,000 lbs qualify for §179 expensing and bonus depreciation without luxury auto limits. A mileage log must be maintained for either method.
What is the Augusta Rule and how can it benefit business owners?
The Augusta Rule (§280A(g)) allows homeowners to rent their primary or secondary residence to their business for up to 14 days per year. The rental income is completely tax-free to the homeowner, and the business deducts the rent as a business expense. At $2,000–$3,000/day for 14 days, this strategy generates $28,000–$42,000 of tax-free income.
How does cost segregation apply to business owners who own real estate?
Cost segregation reclassifies building components into shorter depreciation categories eligible for bonus depreciation. For a $1M commercial property, cost segregation typically identifies $150,000–$250,000 of accelerated depreciation, generating $60,000–$100,000 in first-year deductions at the 100% bonus depreciation (restored by OBBBA for property placed in service after Jan 19, 2025) rate in 2026.
What is the self-employed health insurance deduction?
Self-employed professionals can deduct 100% of health insurance premiums (for themselves, their spouse, and dependents) as an above-the-line deduction under §162(l). This deduction reduces AGI and is available even if the taxpayer does not itemize. S-Corp owners must include premiums in W-2 wages before claiming the deduction.
How should a self-employed professional handle estimated tax payments?
Self-employed professionals must make quarterly estimated tax payments by April 15, June 15, September 15, and January 15. The safe harbor is 100% of prior year tax (110% if prior year AGI exceeded $150,000). Failure to pay sufficient estimated taxes results in an underpayment penalty under §6654.
How should a client establish a mega backdoor Roth to maximize after-tax contributions in 2026?
To set up a mega backdoor Roth, the client must first confirm their employer's 401(k) plan permits after-tax contributions and in-service withdrawals or in-plan Roth conversions. For 2026, the total 401(k) contribution limit, including employee pre-tax, Roth, and after-tax contributions, is $69,000 for individuals under 50, and $76,500 for those 50 or older. The client should elect to contribute the maximum allowable after-tax amount up to these limits, then convert those funds to a Roth IRA or Roth 401(k) as soon as possible to avoid earnings accumulation. Timing and plan-specific rules are critical for avoiding unintended tax consequences.
What steps must be taken to properly report and file a mega backdoor Roth conversion on the client's tax return?
When the client executes a mega backdoor Roth conversion, Form 1099-R will report the distribution from the after-tax account. The tax preparer must carefully complete Form 8606 to report the non-taxable basis and conversion of after-tax contributions. It is essential to maintain records substantiating the after-tax contributions to avoid IRS challenges. The conversion amount generally should not be included in gross income, but any earnings on after-tax contributions before conversion are taxable. Filing deadlines align with the regular Form 1040 deadline, including extensions.
What compliance risks and audit triggers should tax professionals watch for with mega backdoor Roth strategies?
IRS scrutiny often focuses on whether after-tax contributions were properly tracked and whether conversions were timely executed to avoid earnings taxation. A common audit trigger is failure to file Form 8606 or incorrect reporting of basis, leading to double taxation. Additionally, if the plan does not officially allow after-tax contributions or in-service withdrawals, the IRS may disallow the mega backdoor Roth. Professionals should ensure plans comply with IRC §401(a)(4) nondiscrimination rules and document all transactions thoroughly.
What documentation is required to substantiate mega backdoor Roth contributions and conversions during an IRS examination?
Tax professionals should retain detailed plan statements showing after-tax contributions, dates and amounts of in-service withdrawals or in-plan conversions, and corresponding Form 1099-Rs. Documentation should clearly separate after-tax contributions from pre-tax amounts to support basis calculations on Form 8606. Maintaining plan documents evidencing the employer's authorization of after-tax contributions and in-service distributions is advisable. These records help defend against IRS challenges regarding the timing and taxability of conversions.
How does the mega backdoor Roth compare to a standard backdoor Roth IRA in terms of contribution limits and tax planning?
The mega backdoor Roth allows for significantly higher after-tax contributions via the 401(k) vehicle, aggregating up to $69,000 in 2026 including employee deferrals and employer contributions, compared to the $7,500 annual Roth IRA contribution limit. Unlike the traditional backdoor Roth IRA, which involves nondeductible IRA contributions converted to Roth, the mega backdoor Roth uses after-tax 401(k) contributions converted either in-plan or rolled over. This strategy can accelerate Roth accumulation but requires an accommodating 401(k) plan and careful coordination to avoid the pro-rata rule per IRC §408A.
If a client has both a traditional backdoor Roth IRA and a mega backdoor Roth via their 401(k), can they combine these strategies in the same tax year?
Yes, clients can utilize both strategies in the same tax year, but each has distinct IRS reporting requirements and potential tax implications. The traditional backdoor Roth involves nondeductible IRA contributions converted to a Roth IRA, subject to the pro-rata rule under IRC §408(d)(2)(B), which aggregates all IRA balances. The mega backdoor Roth utilizes after-tax 401(k) contributions and conversions, reported separately on Form 1099-R. Coordinating timing and documentation is key to minimizing taxable income and avoiding errors on Forms 8606 and 1099-R.
What client questions should tax professionals ask to determine suitability for implementing a mega backdoor Roth strategy?
Professionals should inquire whether the client’s 401(k) plan permits after-tax contributions and in-service withdrawals or in-plan Roth conversions, as these are prerequisites. It's important to assess the client’s total compensation and ability to maximize contributions up to the $69,000 2026 limit. Understanding the client’s current IRA balances is necessary to anticipate pro-rata rule impacts on related Roth conversions. Finally, professionals should discuss the client’s long-term tax planning goals, liquidity needs, and willingness to maintain detailed records for compliance.

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