What Startup Founders Need to Know About the 2026 Capital Gains Tax Landscape

You spend years building a company, negotiating financing rounds, and working toward an eventual exit. Then the acquisition offer finally arrives, or IPO discussions become real.

Most founders immediately focus on valuation and headline numbers.

The problem is that your final proceeds are not determined solely by deal value. Tax treatment can materially change what actually ends up in your bank account, and the tax picture in 2026 looks different from what it did even a year ago.

Recent legislative changes, including the One Big Beautiful Bill Act signed into law in 2025, preserved important parts of the prior tax framework while keeping several rules founders need to understand.

For startup founders approaching liquidity events, three variables often matter most:

• Long-term capital gains rates
• Qualified Small Business Stock treatment under Section 1202
• Net Investment Income Tax rules

Understanding these factors before an exit process begins can significantly affect planning decisions.

Long-Term Capital Gains Rates Still Matter

For shares held longer than twelve months, gains generally qualify for long-term capital gains treatment.

Current rates remain:

• 0 percent
• 15 percent
• 20 percent, depending on income levels

The One Big Beautiful Bill Act preserved the broader TCJA rate structure and maintained the top 20 percent rate thresholds.

For founders, this matters because holding periods can dramatically affect tax outcomes.

Selling shares before qualifying for long-term treatment can create significantly different tax consequences.

QSBS May Be the Most Valuable Founder Tax Benefit Available

For many startup founders, Section 1202 Qualified Small Business Stock rules create one of the largest planning opportunities available.

QSBS potentially allows founders and early investors to exclude up to:

• $10 million of capital gains
• Or ten times adjusted basis, whichever is greater

For companies and founders who qualify, the impact can be enormous.

However, the requirements matter.

To qualify:

• The company must have had less than $50 million in assets when shares were issued
• Shares generally must be held longer than five years
• The company must be a C corporation engaged in a qualifying business activity

Many founders assume QSBS automatically applies across all stock holdings.

That assumption often creates surprises.

The Net Investment Income Tax Adds Another Layer

Even founders already planning for capital gains taxes sometimes overlook the Net Investment Income Tax, commonly called NIIT.

The NIIT adds an additional 3.8 percent surtax on investment income for taxpayers above certain income thresholds:

• $200,000 for single filers
• $250,000 for married filers

For meaningful startup exits, many founders exceed these thresholds. Importantly, the surtax remains in place under current law.

Founders sometimes focus entirely on capital gains rates and underestimate the impact of additional taxes on overall proceeds.

State Taxes Can Change Exit Economics

Federal treatment is only part of the picture. State tax treatment varies significantly and can materially change outcomes.

California creates one of the most common examples. Unlike federal rules, California taxes capital gains as ordinary income and does not provide a state QSBS benefit.

For founders in higher tax jurisdictions, state taxes can substantially affect net proceeds after a transaction closes.

This is one reason sophisticated exit modeling often includes both federal and state-level analysis.

Timing Decisions Often Matter Years Earlier Than Founders Expect

Many founders think exit tax planning starts once acquisition discussions begin. Usually, major tax outcomes depend on decisions made years before any term sheet appears.

Examples include:

• Option exercise timing
• 83(b) election decisions
• Holding periods
• Entity structure choices
• Stock issuance timing

By the time a deal is signed, many of the most important tax variables may already be fixed.

Common Founder Mistakes

• Waiting Until The Exit Process Starts: Many founders begin thinking about taxes only after a term sheet appears. By then, many important planning opportunities have already passed. Decisions affecting tax outcomes often start years before an acquisition or IPO process begins.
• Assuming QSBS Applies Automatically: QSBS has very specific eligibility requirements and not every startup qualifies. Industry restrictions, asset thresholds, and issuance timing can all affect treatment. Founders should verify eligibility grant by grant rather than relying on assumptions.
• Ignoring State Tax Treatment: Federal treatment receives most of the attention during exit planning discussions. State tax rules can materially change net proceeds and sometimes produce very different outcomes. California remains one of the clearest examples.
• Overlooking NIIT Exposure: Founders sometimes focus on capital gains rates while forgetting the additional 3.8 percent surtax. Large exits often trigger NIIT exposure automatically. Ignoring it can create inaccurate payout expectations.

10 Minute Founder Self Check

Before entering an acquisition or IPO process, ask:

• Do you know the acquisition date for each block of shares?
• Have you verified QSBS qualification under Section 1202?
• Have you modeled NIIT exposure?
• Do you understand how your state taxes capital gains?
• Have tax advisors reviewed the structure before signing a deal?

If several of these answers remain unclear, your exit planning may not be as complete as you think.

Understanding Your Exit Economics Starts Long Before The Exit

Founders often think valuation determines success. In reality, taxes, structure, and long-term planning decisions can materially change what founders actually keep after a transaction closes.

Schedule a free discovery call with our team today to learn more about startup growth and fundraising considerations as companies move toward major liquidity events.

Book here: https://calendly.com/primumlaw/30min

Sources Used

• IRS Section 1202 Qualified Small Business Stock — Internal Revenue Service, https://www.irs.gov
• One Big Beautiful Bill Act Tax Provisions Summary — Tax Foundation, https://taxfoundation.org
• Capital Gains Tax Rates 2026 — Tax Policy Center, https://www.taxpolicycenter.org