Selling shares in a private company triggers federal income tax on the difference between what you paid for the stock and what you received for it, at rates that run from 0% to more than 37% depending on how you got the shares and how long you held them. The tax implications of selling shares in a private company are shaped less by the sale itself than by decisions made months or years earlier: how the equity was granted, whether an election was filed on time, whether the company qualifies as a small business under Section 1202, and how the deal is papered. For many founders and early employees, the tax bill is the single largest cost of a liquidity event, and most of the tools to reduce it have to be in place before closing.
How Your Gain Is Calculated and Taxed
Your taxable gain equals the sale proceeds minus your adjusted basis. Basis is usually what you paid for the stock plus any additional capital you put in. If you got the shares through options or restricted stock, basis is calculated differently, and that’s covered further down.
Holding period drives the rate. Shares held more than one year produce long-term capital gains, taxed at 0%, 15%, or 20% depending on your income and filing status.1Internal Revenue Service. Topic No. 409, Capital Gains and Losses Shares held a year or less are short-term, taxed at ordinary rates reaching 37% federally.
A private company sale usually pushes the seller into the top bracket for the year. On top of the capital gains rate, sellers with modified adjusted gross income above $200,000 (single) or $250,000 (married filing jointly) owe an additional 3.8% Net Investment Income Tax on the lesser of net investment income or the amount by which income exceeds the threshold.2Internal Revenue Service. Net Investment Income Tax Those thresholds don’t adjust for inflation. A high-income founder selling long-held stock will pay a combined federal rate of 23.8% before state taxes.
The Qualified Small Business Stock Exclusion
Section 1202 is the most valuable break available to sellers of private company stock. It lets an individual taxpayer exclude a large portion of the gain from selling qualified small business stock (QSBS), sometimes reducing federal tax to zero. The rules changed on July 4, 2025 with the enactment of the One, Big, Beautiful Bill, so the requirements depend on when the stock was issued.
Requirements That Apply to All QSBS
The company must be a domestic C corporation. You must have acquired the stock at original issuance, meaning directly from the company in exchange for cash, property, or services, rather than buying it from another shareholder.3Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock
The company also has to pass an active business test for substantially all of your holding period, with at least 80% of assets used in a qualifying active business. Several industries are disqualified, including financial services, banking, insurance, farming, mining, hospitality, and professional services where the main asset is employee skill or reputation. Technology, manufacturing, and retail generally qualify.
Stock Issued Before July 5, 2025
For QSBS acquired after September 27, 2010 and issued before July 5, 2025, you can exclude up to 100% of the gain, capped at the greater of $10 million or 10 times your adjusted basis in the stock, per company.3Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock The stock must be held more than five years, and the company’s aggregate gross assets (measured by tax basis) must not have exceeded $50 million at any point before or immediately after issuance. A founder who paid $1,000 for stock and sells for $8 million after five years can exclude the entire gain and pay zero federal tax.
Stock Issued After July 4, 2025
The new law expands the benefit for stock issued after enactment. The gross assets ceiling rises from $50 million to $75 million. The required holding period drops from more than five years to at least three years. The per-issuer exclusion cap increases to $15 million, or 10 times adjusted basis if greater.3Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock
The cap is per taxpayer, per issuer. If you sell QSBS in Company A and later in Company B, each sale gets its own limit. Founders who paid a nominal amount for their shares should track basis carefully, because the 10x-basis alternative cap barely helps when basis is $1,000.
Documenting a QSBS Claim
The IRS does not pre-certify QSBS status. The burden of proof is on you. Collect documentation from the company covering the gross assets balance at the time your stock was issued, the date of original issuance, and the business activities during your holding period. Board representations or officer certifications on these points are common in acquisition agreements. If the company converted from an LLC or partnership, the gross assets test at conversion may be measured at fair market value rather than tax basis, which complicates the analysis and can warrant a professional valuation.
Deferring Gain With a Section 1045 Rollover
If you sell QSBS before hitting the Section 1202 holding period, you may still defer the gain by rolling proceeds into replacement QSBS. Section 1045 lets a non-corporate taxpayer who has held QSBS for more than six months defer gain by buying new QSBS within 60 days of the sale.4Office of the Law Revision Counsel. 26 USC 1045 – Rollover of Gain From Qualified Small Business Stock to Another Qualified Small Business Stock
Gain is recognized only to the extent proceeds exceed what you spend on the replacement stock, and deferred gain reduces your basis in the new shares. The tax is postponed, not erased. The 60-day window is strict and cannot be extended.
How the Deal Is Structured
Stock Sale vs. Asset Sale
In a stock sale, you sell shares directly to the buyer. Your gain is proceeds minus basis, taxed at capital gains rates. This is the cleanest outcome and the structure most sellers prefer.
In an asset sale, the company sells its underlying business assets. The company recognizes gain and pays corporate-level tax, and the remaining proceeds are distributed to shareholders in liquidation, generating a second layer of tax at the individual level. That double taxation hits C corporation shareholders hardest. S corporations and LLCs generally avoid the corporate-level tax, so an asset sale is less painful for those entity types.
Earnouts and Escrow Holdbacks
Escrow holdbacks reserved for indemnification claims keep the same capital gains character as the rest of the proceeds. When escrow releases, you report additional gain in the year of receipt.
Earnouts create more complexity. If the maximum earnout amount can be determined at closing, you may elect the installment method under Section 453 to spread gain across the years you actually collect. Deferred payments due more than a year after the sale may carry an imputed interest component under Section 483, taxed as ordinary income at the applicable federal rate in effect at the time of the sale.5Office of the Law Revision Counsel. 26 USC 483 – Interest on Certain Deferred Payments
Interest Charges on Large Installment Obligations
Section 453A applies when the face amount of installment obligations arising in a tax year exceeds $5 million. Above that threshold, the seller pays an interest charge to the IRS on the deferred tax liability each year the obligation is outstanding, tied to the IRS underpayment rate.6Office of the Law Revision Counsel. 26 USC 453A – Special Rules for Nondealers On large earnouts, the interest cost can erode much of the deferral benefit. Some sellers do better recognizing the gain upfront.
How You Got the Shares Changes the Answer
Founders and employees rarely buy shares outright at fair market value. How the equity was granted determines both your basis and whether part of the sale proceeds gets taxed at ordinary rates rather than capital gains rates.
Non-Qualified Stock Options
With NSOs, the tax event is at exercise. The spread between fair market value on the exercise date and your exercise price is ordinary income and appears on your W-2.7NASPP. Tax Withholding and Reporting for Equity Awards That amount becomes your basis. Only gain above basis is taxed as a capital gain when you sell, and the long-term holding clock starts on the exercise date.
Incentive Stock Options
ISOs get no regular income tax at grant or exercise, but the spread at exercise is an adjustment for the Alternative Minimum Tax and can produce a surprise bill in the exercise year. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, phasing out beginning at $500,000 and $1,000,000 respectively.8Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
To get full long-term capital gains treatment, you must hold the shares at least two years after grant and at least one year after exercise.9Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options Selling before hitting both is a disqualifying disposition, and the spread at exercise is reclassified as ordinary income. In an acquisition, hitting both holding periods is often impossible, so many ISO holders end up disqualified regardless.
RSUs, RSAs, and the 83(b) Election
With restricted stock units, the full fair market value at vesting is ordinary income on your W-2. That value is your basis, and any later gain or loss is measured from the vesting date.10Morgan Stanley at Work. Restricted Stock, Performance Stock Awards and Taxes – What to Know If the sale follows soon after vesting, there may be little additional gain.
Restricted stock awards default to the same treatment, but they offer something RSUs don’t. Under Section 83(b), you can elect to recognize ordinary income at grant instead of at vesting. Made when the stock is worth almost nothing, the election costs a trivial amount of ordinary tax, starts the capital gains holding clock immediately, and pushes all future appreciation into capital gains territory.
The 83(b) election must be filed with the IRS within 30 days of grant using Form 15620, with a copy to the company.11Internal Revenue Service. Form 15620, Section 83(b) Election Missing the deadline is fatal. No extension, no cure, no appeal. It is one of the most expensive mistakes in startup tax planning.
Selling at a Loss: Section 1244
If the shares sell at a loss, the default treatment is a capital loss, deductible only against capital gains plus $3,000 of ordinary income per year. Large losses take years to absorb at that pace.
Section 1244 changes that math. If the company qualifies as a small business corporation that received no more than $1 million in total money and property for its stock, losses on that stock can be treated as ordinary losses up to $50,000 per year, or $100,000 for married couples filing jointly.12Office of the Law Revision Counsel. 26 USC 1244 – Losses on Small Business Stock Ordinary losses offset all income without the $3,000 annual cap. The stock has to have been issued directly to you for money or property, and you must be an individual taxpayer.
Estimated Tax Payments After the Sale
A private company sale usually produces a one-time income spike that dwarfs normal earnings. Without estimated payments to cover the extra tax, the IRS charges an underpayment penalty calculated quarterly.
The safe harbor is paying the lesser of 90% of the current year’s tax or 100% of last year’s tax. If prior-year adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the second prong rises to 110% of last year’s tax.13Internal Revenue Service. 2026 Form 1040-ES, Estimated Tax for Individuals The 110% prong is usually the easiest to hit, because last year’s liability was based on normal earnings.
If the sale closed late in the year, look at the annualized income installment method on Form 2210, Schedule AI. It recalculates required payments based on when the income was actually received rather than spreading it evenly across quarters. A seller whose deal closed in November would not owe estimated payments in earlier quarters based on the sale proceeds.14Internal Revenue Service. Instructions for Form 2210 The form is tedious but can eliminate penalties for back-loaded income.
Reporting the Sale
Private company stock sales go on Form 8949, listing each lot with acquisition and sale dates, proceeds, and basis. Gains and losses are classified as short-term or long-term on that form, and the totals carry to Schedule D and then Form 1040.15Internal Revenue Service. About Form 8949, Sales and Other Dispositions of Capital Assets
Unlike public stock, private sales usually don’t generate a Form 1099-B. You have to reconstruct basis and dates from purchase agreements, option exercise records, grant letters, and cap table data. Keep those documents permanently. In an audit, the burden is on you to prove basis and holding period.
QSBS exclusions are reported on Form 8949 using a specific adjustment code. Expect to substantiate the holding period (five years, or three for post-July 2025 stock), the company’s gross assets when your stock was issued, and its compliance with the active business test throughout your holding period.16Internal Revenue Service. 2025 Instructions for Form 8949 – Sales and Other Dispositions of Capital Assets
State Taxes and QSBS Non-Conformity
Most states tax capital gains at the same rate as ordinary income. Top marginal rates range from zero in states without an income tax to above 13% in the highest-tax states. Your state of residence on the sale date generally decides which state taxes the gain.
The federal QSBS exclusion does not automatically follow to the state return. Many states do not conform to Section 1202, meaning the full gain can be state-taxable even when the federal tax is zero. Sellers in non-conforming states sometimes discover the state bill is their only tax on the transaction, which is a shock if they assumed the exclusion covered everything. Check state conformity before closing.
If the company did business in states other than where you live, those states may claim a share of the gain. That’s more common in asset sales, where the business nexus is clearer, but some states press the point on stock sales too. Sellers with multistate exposure should budget for non-resident filings and potential apportionment disputes.