OBBBA Mid-Year Tax Audit: 5 Moves Every Solo Founder Should Make Before September 15

Every year has a tax rhythm. Most founders feel it as a series of unpleasant surprises — a Q4 scramble, an underpayment penalty, a missed deduction window. But 2026 is different, and it rewards the operators who treat their tax position the way they treat their P&L: as a system to be monitored mid-year, not just reconciled in April. The One Big Beautiful Bill Act (OBBBA), signed into law on July 4, 2025, changed enough of the underlying rules that the right OBBBA tax strategy for founders in 2026 starts now — specifically, before the September 15 Q3 estimated-tax deadline.

This is not a post about general budgeting. It is a mid-year audit checklist for bootstrapped operators and exit-oriented builders with $80K or more in annual profit. If you run a pass-through entity — sole proprietorship, single-member LLC, partnership, or S-corp — the five moves below are the ones that will matter most between now and December 31.

Last updated: June 7, 2026.

This is general information, not tax or financial advice. Consult a qualified CPA or tax professional before making decisions based on your specific situation.

What OBBBA Actually Changed (The Numbers That Matter)

Before the checklist, a quick systems-level summary of the OBBBA provisions that are live for the 2026 tax year. These are the inputs that change your estimated tax math.

Sources: BDO — OBBBA Expands 100% Depreciation Expensing; Kitces — Breaking Down the OBBBA; Landmark CPAs — QBI Deduction 2026 Changes.

One clarification worth making explicit: the House version of OBBBA proposed raising the QBI deduction from 20% to 23%. That increase was stripped in the final Senate version. The deduction stays at 20% — but its permanent status and the widened phaseout ranges are still materially valuable for operators near the threshold.

Move 1: Recompute Your QBI Deduction With 2026 Phaseout Numbers

The §199A deduction lets pass-through owners deduct up to 20% of qualified business income before calculating income tax. For a founder running $150,000 of profit through a single-member LLC, that’s a $30,000 deduction — real money that many operators underestimate because they calculated it under old phaseout rules and concluded they didn’t qualify.

Under OBBBA, the phaseout range is now $75,000 wide (single) and $150,000 wide (joint), up from $50,000 and $100,000 respectively. That means you can have more income inside the phaseout band before the deduction zeros out — and some founders who were fully phased out in 2025 will partially qualify in 2026.

Worked example (single filer, non-SSTB): If your total taxable income is $230,000 and the phaseout begins at $197,300 (approximate 2026 threshold for single filers), you are $32,700 into the phaseout range. With a $75,000 wide band, you’ve used 43.6% of the range, so your QBI deduction is reduced by 43.6% — meaning you still get roughly 56.4% of your full 20% deduction. On $150,000 of QBI that’s approximately $16,920 rather than zero. Check your 2025 return: if you got nothing, run the 2026 math again.

If you run a Specified Service Trade or Business (SSTB — consulting, financial services, law, health) the phase-out rules are more aggressive. At income above the upper threshold (~$272,300 single / ~$544,600 joint), the deduction goes to zero. For SSTB operators near those thresholds, income timing and retirement contributions become critical levers before September 15.

Move 2: True-Up Your Estimated Tax Payments Before September 15

The Q3 estimated tax deadline is September 15, 2026. This is the moment in the year where most founders are running at enough actual revenue to make an informed projection — not guessing, the way they were in April. Use that data.

The safe-harbor rule (IRS Publication 505) says you avoid underpayment penalties by paying the lesser of: (a) 100% of last year’s tax liability (110% if your 2025 AGI exceeded $150,000), or (b) 90% of your 2026 actual liability. For most growing businesses, option (a) anchors you to a lower number that may not reflect your actual trajectory.

Mid-year projection process:

1. Pull your YTD revenue and expenses through June 30.
2. Annualize the net profit (multiply by 2 if your business is roughly linear, or model seasonality if it isn’t).
3. Apply the 20% QBI deduction to your projected QBI.
4. Run your projected taxable income through the 2026 brackets.
5. Subtract payments already made (Q1 April 15, Q2 June 15).
6. Divide the remaining liability roughly in half across Q3 (Sep 15) and Q4 (Jan 15, 2027).

If you are an S-corp owner, also factor in the payroll taxes on your W-2 salary — those are separate from estimated income tax and flow through the payroll cycle, not the 1040-ES system. The salary you set as an S-corp owner directly affects both your FICA exposure and your QBI deduction ceiling (see Move 3 for the full interaction).

Move 3: Review Your S-Corp Reasonable Salary Before Year-End

If you are an S-corp owner, the salary/distribution split is the most powerful payroll-tax lever you have — and it needs to be calibrated annually, not set-and-forgotten. The IRS requires that you pay yourself a “reasonable salary” for the services you perform. Too low a salary triggers audit risk; too high a salary unnecessarily exposes profit to FICA taxes (15.3% up to the $176,100 Social Security wage base for 2026, then 2.9% Medicare on everything above — IRS Topic 751).

The general heuristic most CPAs use is 30–50% of net profit as the salary, but the correct number is market-rate compensation for your role. Here is what the math actually looks like across two scenarios:

Breakeven point: S-corp election typically pays off above approximately $60,000 in net profit, after accounting for the added administrative cost of running payroll (roughly $1,500–$2,500/year for a payroll service) and filing a separate S-corp return (Form 1120-S, typically $500–$1,500 additional CPA cost). Below $50,000–$60,000 in net profit, the overhead usually exceeds the FICA savings — stay a sole prop or single-member LLC.

The OBBBA wrinkle: Your QBI deduction is limited to the greater of 50% of W-2 wages paid or 25% of W-2 wages plus 2.5% of qualified property. That means the salary you set directly affects your QBI deduction ceiling. Setting your salary too low to save payroll tax can inadvertently reduce your QBI deduction. Model both variables together — they interact. At $80,000 W-2, the QBI wage limit is $40,000 (50% × $80K); your $150K profit at 20% QBI = $30,000 deduction, which is under that cap, so you’re fine. But if you drop salary to $40,000 trying to save FICA, your QBI wage cap drops to $20,000 — and if your business scales, that ceiling bites.

This is general information, not tax or financial advice — consult a CPA or tax professional who specializes in S-corp structuring before adjusting your salary.

Move 4: Plan Any Equipment Purchases Before December 31

The restoration of 100% bonus depreciation under OBBBA is one of the most founder-favorable provisions in the law. Any qualifying asset — computers, servers, software, equipment with a 20-year or shorter MACRS class life — placed in service before December 31, 2026 can be fully expensed in the year of purchase. No depreciation schedules. No partial-year calculations.

Section 179 runs alongside bonus depreciation with a $2.56M ceiling (inflation-adjusted) and a phaseout that doesn’t begin until $4.09M of total asset purchases — well above what any solo founder is likely to spend. For most bootstrapped operators, the practical distinction is small: both routes get you to 100% immediate expensing on qualifying purchases.

The mid-year decision framework:

• If you need equipment or software in the next 6 months, pull the purchase into 2026 to guarantee the deduction lands this tax year.
• If you were planning a major equipment investment for early 2027, run the math: the deduction is permanent now, so timing is less urgent than it was under the phasedown — but accelerating the purchase still accelerates the deduction.
• If the asset would be financed, here is the complete math: A $30,000 equipment purchase at a 22% marginal rate yields $6,600 in immediate tax savings. At 8% financing over 36 months, total interest on that $30,000 is approximately $3,900. That interest is also deductible — at 22%, you recover about $858 of it in tax savings. Net financing cost after tax: roughly $3,042. Net benefit of the deduction minus the financing cost: approximately $3,558 this year — a real positive if your cash flow can handle the payment. If your marginal rate is 37%, the immediate tax savings jump to $11,100, making the $3,042 net financing cost an even easier hurdle to clear.
• Be aware that Section 163(j) interest deduction limitations and Section 263A capitalization rules can interact with accelerated expensing — particularly if you carry inventory. Flag this with your CPA before December.

Move 5: Harvest Deductions and Accelerate Retirement Contributions

The final move is the most straightforward but requires action before December 31 — and ideally before September 15, so you can factor it into your Q3 estimated payment calculation.

Retirement contributions (IRS Retirement Topics — Contributions): If you have a Solo 401(k), your employee deferral limit for 2026 is $23,500 (plus $7,500 catch-up if you’re 50+). Your employer contribution can add up to 25% of W-2 wages (S-corp) or roughly 20% of net self-employment income (sole prop/LLC). Total contribution limit is $70,000 for 2026. Every dollar contributed reduces your AGI dollar-for-dollar — which also directly reduces your QBI phaseout exposure.

Deduction harvesting: Pre-pay deductible business expenses where the timing is genuinely business-driven — subscriptions, professional development, software licenses. The rule is that the expense must be paid and the service must start within 12 months; you can’t pre-pay three years of hosting to manufacture a deduction. But pulling legitimate Q1 2027 expenses into Q4 2026 is clean planning.

Health insurance premiums: If you are a self-employed founder (including S-corp shareholders who own more than 2%), you can deduct 100% of health insurance premiums as an above-the-line deduction. If you’re not tracking this separately and reconciling it annually, you’re likely leaving a clean deduction behind.

The September 15 Deadline: Why It’s the Right Moment

The Q3 estimated-tax deadline is not just a payment date — it’s the last moment in the year where you have enough actual data to make precise projections and enough runway to change outcomes. After September 15, you still have Q4, but your operating leverage decreases: major equipment purchases need lead time, retirement contribution decisions get more complex under year-end cash pressure, and your CPA’s availability narrows.

Treat September 15 as your mid-year board meeting with your own P&L. Run the five moves above as a structured review, not a last-minute scramble. The founders who use the OBBBA well in 2026 will not be the ones who learned about it in March 2027 — they’ll be the ones who updated their tax model in July.

FAQ: OBBBA Tax Strategy for Founders 2026

What is the Q3 estimated tax deadline for self-employed founders in 2026?

The Q3 estimated tax deadline for self-employed founders is September 15, 2026. Miss it and you risk an underpayment penalty on Q3 income. If you cannot pay the full amount, pay at least the safe-harbor minimum (100% of last year’s tax, or 110% if your 2025 AGI exceeded $150,000) to avoid the penalty on the underpaid portion.

Did the OBBBA increase the QBI deduction from 20% to 23%?

No. The House version proposed raising the §199A QBI deduction from 20% to 23%, but the Senate stripped that increase before final passage. The deduction stays at 20% of qualified business income — but it is now permanent (it was set to expire end of 2025 under TCJA) and the phaseout ranges are widened, so more founders will qualify for a full or partial deduction in 2026.

How do I calculate my QBI deduction if I’m near the phaseout threshold in 2026?

Determine how far your taxable income falls into the phaseout band (starts at ~$197,300 single, $394,600 joint for 2026; band is $75,000 wide single / $150,000 wide joint). Divide that excess by the band width to get your reduction percentage. Multiply your full 20% QBI deduction by (1 − reduction%). Example: $32,700 into a $75,000 band = 43.6% reduction; you retain 56.4% of your deduction. Consult a CPA or use IRS Form 8995-A for the full calculation.

Should I set up a Solo 401(k) before September 15, 2026?

Yes, if you are self-employed and do not already have one. The Solo 401(k) plan must be established by December 31, 2026 to make 2026 contributions, but setting it up before September 15 lets you factor the contribution into your Q3 estimated tax calculation. A $23,500 employee deferral (plus employer contributions up to the $70,000 total limit) directly reduces your AGI, which can pull you below QBI phaseout thresholds and reduce your Q3 payment.

How much can I contribute to a Solo 401(k) in 2026?

The total Solo 401(k) contribution limit for 2026 is $70,000 (IRS Retirement Topics — Contributions). This combines the employee deferral ($23,500, plus $7,500 catch-up if age 50+) and the employer contribution (up to 25% of W-2 wages for S-corp owners, or approximately 20% of net self-employment income for sole proprietors and single-member LLCs).

How does bonus depreciation interact with Section 179 under OBBBA?

Both provisions now deliver 100% immediate expensing for qualifying assets placed in service in 2026, but they apply in a specific order: Section 179 applies first, then bonus depreciation covers remaining basis. Section 179 is capped at $2.56M (2026 inflation-adjusted) and phases out above $4.09M in total asset purchases. Bonus depreciation has no dollar cap but cannot create a net operating loss above the $256,000 excess business loss threshold for single filers in 2026 (deferred to future years). Your CPA can help you sequence these to maximize current-year benefit while managing loss limitation rules.

I’m an S-corp owner. Should I adjust my salary before the September 15 deadline?

Potentially, yes — but model the salary/distribution/QBI interaction together before changing anything. Your W-2 salary sets the ceiling for your QBI deduction (50% of W-2 wages for non-capital-intensive businesses). Lowering salary to cut FICA can inadvertently reduce your QBI deduction and cost more in income tax than you saved on payroll tax. Mid-year is the right time to run this model; changing payroll in Q4 is administratively cleaner than unwinding a change after year-end. Consult a qualified professional — this is general information, not tax advice.

Does S-corp election affect QSBS eligibility for exit-oriented founders?

Yes — this is a critical interaction that exit-planning founders must understand. S-corps do not qualify for the Section 1202 QSBS exclusion. If you converted from a C-corp to an S-corp, stock issued after the conversion date loses QSBS eligibility. If you are still a C-corp considering S-corp election purely for FICA savings, model whether the payroll-tax benefit outweighs potential loss of up to $10M in QSBS gain exclusion. Consult a tax attorney before electing S-corp status if an exit is on your horizon.

Conclusion: Build the Tax System, Not Just the Filing

The OBBBA changes are not a one-time event — they are a new baseline. The permanent QBI deduction, restored 100% bonus depreciation, and elevated Section 179 limit are now infrastructure, not temporary windows. The founders who will compound the most value out of these rules are the ones who integrate them into quarterly operating rhythm rather than treating tax as an annual event.

A concrete benchmark: A founder with $150,000 in net profit who correctly applies the permanent QBI deduction, maximizes Solo 401(k) contributions (employee deferral + employer match), and routes equipment purchases through 100% bonus depreciation could reduce 2026 federal taxable income by $55,000–$65,000 before any state-level strategies — a real five-figure difference that compounds forward into reinvested capital.

Your concrete next step before September 15: open your YTD P&L, run the five-move checklist above, and book 30 minutes with your CPA to pressure-test the projections. The best OBBBA tax strategy for founders in 2026 is one that runs in the background like a well-tuned system — not one that fires as a crisis in Q1 2027.

Disclaimer: This post is for general informational purposes only and does not constitute tax, legal, or financial advice. Tax laws are complex and fact-specific. Consult a licensed CPA, enrolled agent, or tax attorney before making decisions based on this content.