A founder we worked with had $20 million in QSBS gains on the table this year and ran the numbers three different ways before finding out what they'd actually keep. Hold the stock three years and the IRS takes $6.36 million. Hold it five and they take nothing. That's not a rounding error. It's the entire difference between a good exit and a life-changing one, and almost no founder runs this math until the term sheet is already on the table. Here's the actual QSBS tax savings example, using the rules that changed in July 2025, and the one date that decides which version of the math applies to you.
The math nobody shows you before the term sheet
QSBS, or Qualified Small Business Stock under Section 1202, lets founders exclude some or all of their capital gains tax on a sale, if the stock qualifies and you've held it long enough. Before July 2025, the rule was simple and brutal: hold five years, exclude up to $10 million (or 10 times your basis, whichever is bigger), or get nothing. One day short of five years and you're back to paying full capital gains rates.
The One Big Beautiful Bill Act changed that, but only for stock issued after July 4, 2025. For that stock, the five-year cliff became a ladder: hold three years and exclude 50% of the gain, hold four and exclude 75%, hold five and you're back to the full 100%. The dollar cap also went up, from $10 million to $15 million, indexed to inflation going forward.
Run the same $20 million gain through both timelines and the difference is stark. At the old flat rate with a three-year hold, you get zero exclusion and pay roughly $6.36 million in federal tax (28% capital gains plus 3.8% net investment income tax). Under the new tiered system with that same three-year hold, you exclude 50%, or $10 million, and pay tax on the remaining $10 million, about $3.18 million. Wait one more year and the exclusion jumps to 75%, cutting your tax bill to roughly $1.59 million. Hold the full five and the federal bill on that $20 million goes to zero.
The mistake that costs founders the most
Here's what trips people up, and it's not the math. It's the date. The tiered exclusion only applies to stock acquired after July 4, 2025. If your shares were issued before that date, you're still on the old rules: a hard five-year requirement, a $10 million cap, no partial credit for years three and four.
We've seen founders read a headline about "QSBS now works after three years" and assume it applies to options or founder shares they were issued back in 2022 or 2023. It doesn't. Your acquisition date is fixed the moment the stock is issued, not the moment you decide to sell, and not the moment a new law passes. If you have multiple tranches of stock issued at different times, which is common after option exercises, follow-on grants, or a refresh, each tranche gets evaluated on its own issuance date and its own clock.
The second mistake is assuming QSBS status is guaranteed just because you're a C-corp. It isn't. The company has to stay under $50 million in gross assets at the time the stock was issued, has to be an active business (not a holding company or certain excluded industries like professional services, finance, or hospitality), and the stock has to be acquired directly from the company, not bought from another shareholder on the secondary market.
The exact calculation, step by step
- Confirm your stock's issuance date on your cap table, not your start date at the company.
- Check whether that date is before or after July 4, 2025, since that decides which rule set applies.
- Confirm the company met the $50 million gross assets test at issuance and has stayed an active qualified trade or business since.
- Calculate your holding period as of the expected closing date, not today.
- Apply the correct exclusion percentage: 100% if pre-July 2025 stock held five-plus years, or the applicable tier (50/75/100%) if issued after July 4, 2025.
- Apply the dollar cap: the greater of $10M or $15M (depending on issuance date) or 10 times your adjusted basis in the stock.
- Calculate federal tax on the non-excluded portion at 28% plus 3.8% NIIT, then check your state's treatment separately, since not every state honors the federal exclusion.
What this looked like for one exit
The founder in our example had two tranches: an early batch of founder shares issued in 2021, well past the five-year mark and fully eligible for the old $10 million cap at 100% exclusion, and a second batch from a 2025 option exercise, issued in September, after the July 4 cutoff. That second tranche was only three years from a five-year hold at the time of the offer.
Running both tranches separately meant the 2021 shares excluded $10 million tax-free outright. The 2025 tranche, sold at the three-year mark, only qualified for the 50% tier on its portion of the gain. Waiting eighteen more months to cross the four-year threshold on that tranche alone was worth roughly $900,000 in additional exclusion. That's the kind of number that changes whether you take a deal this quarter or push the close date.
The one thing to check this week
Pull your cap table and note the issuance date on every tranche of stock you hold, not just the total share count. If you're anywhere near a sale conversation, get a QSBS eligibility opinion from a tax attorney now, not during diligence. It's the cheapest insurance policy you'll buy this year, and it's the only way to know which version of this math actually applies to your shares before you're negotiating a closing date under pressure.
Frequently asked questions
How much does QSBS actually save a founder?
It depends on the gain size, the exclusion cap that applies to your stock's issuance date, and how long you've held it. On a $20 million gain, the difference between a three-year hold and a five-year hold under the new rules is roughly $4.77 million in federal tax.
Does the new 3-year QSBS rule apply to stock I already own?
Only if it was issued after July 4, 2025. Stock issued on or before that date still needs a full five-year hold for any exclusion, under the old $10 million cap.
What disqualifies a company from QSBS?
Gross assets over $50 million at the time the stock was issued, being in an excluded industry like professional services or finance, or the company failing to remain an active qualified trade or business.
Do I need a lawyer to confirm QSBS eligibility?
Yes, before you're in a live deal. Eligibility depends on facts specific to your cap table and your company's history, and getting it wrong after closing is far more expensive than confirming it beforehand.
Does every state honor the federal QSBS exclusion?
No. Several states, including California, do not conform to the federal exclusion and tax the gain in full at the state level, so check your state's treatment separately from the federal math.