Tax Implications of Selling Shares in a Private Company

The tax implications of selling shares in a private company start with a simple formula and get complicated fast: you owe federal tax on the difference between what you paid for the stock and what you receive for it, at rates that range from 0% to over 37% depending on how long you held the shares and how you acquired them. For founders and early employees, the tax bill is often the single largest cost of a liquidity event. Several provisions can cut that bill sharply, sometimes to zero, but almost all of them depend on steps taken months or years before the deal closes.

How the Gain Is Calculated and Taxed

Your taxable gain equals the sale proceeds minus your adjusted basis. Basis is usually what you paid for the shares plus any additional capital you contributed. If you received the stock through options or a restricted stock grant, basis is calculated differently, and that calculation is covered further down.

Holding period determines the rate. Shares held more than one year produce long-term capital gains, taxed at 0%, 15%, or 20% depending on your total taxable income and filing status.¹ Shares held a year or less are short-term, taxed at ordinary income rates that reach 37% federally.

A large sale often 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 their net investment income or the amount their income exceeds the threshold.² Those thresholds don’t adjust for inflation. So a high-income founder selling long-held shares pays a combined federal rate of 23.8% before any state tax.

The QSBS Exclusion: The Biggest Lever

Section 1202 of the Internal Revenue Code is the most valuable break available to sellers of private company stock. It lets individual taxpayers exclude a large share of their gain from selling qualified small business stock (QSBS), sometimes eliminating the federal tax entirely. The rules changed on July 4, 2025, when the One, Big, Beautiful Bill was enacted, so the requirements depend on when the stock was issued.

Requirements That Apply to Any QSBS Claim

Every QSBS claim rests on the same foundation. The company must be a domestic C corporation. You must have acquired the stock at original issuance, directly from the company in exchange for cash, property, or services, rather than buying it from another shareholder.³ At least 80% of the corporation’s assets must be used in an active qualified business for substantially all of the holding period. Several industries are disqualified, including financial services, banking, insurance, farming, mining, hospitality, and professional service businesses whose main asset is employee skill or reputation. Most technology companies, manufacturers, and retailers qualify.

Stock Issued Before July 5, 2025

For stock 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.³ You must hold the stock for more than five years. The company’s aggregate gross assets (measured by tax basis) could not have exceeded $50 million at any time before issuance or immediately after. A founder who paid $1,000 for stock and sells for $8 million would exclude the entire gain and owe zero federal tax on it.

Stock Issued After July 4, 2025

The new law expanded QSBS in three ways for stock issued after enactment. The gross assets threshold rose from $50 million to $75 million, opening the exclusion to larger startups. The holding period dropped from more than five years to at least three. And the per-issuer cap rose to $15 million, or 10 times your adjusted basis if greater.³

The cap is per issuer and per taxpayer. If you sell QSBS in Company A and later in Company B, each sale gets its own exclusion limit. Founders who paid a nominal amount for their shares should track basis carefully, because the 10x-basis alternative does little when basis is $1,000.

Documenting the Claim

The IRS does not pre-certify QSBS status, so the burden of proof falls on you. Before or during the sale, collect documentation from the company showing the gross assets balance when your stock was issued, the date of original issuance, and the company’s business activities throughout your holding period. Board representations or officer certifications covering these points are common in acquisition agreements. If the company converted from an LLC or partnership, the gross assets analysis gets more complicated, and an early professional valuation is advisable for companies near the threshold.

If You Sold QSBS Too Early: The Section 1045 Rollover

If you sell QSBS before meeting the Section 1202 holding period, you may still defer the gain by rolling the proceeds into replacement QSBS. Section 1045 allows a non-corporate taxpayer who has held QSBS for more than six months to defer gain recognition by purchasing new QSBS within 60 days of the sale.⁴

Gain is recognized only to the extent the proceeds exceed what you spend on the replacement stock. Deferred gain reduces your basis in the new shares, so the tax is postponed rather than erased. The strategy helps most when an early secondary sale or tender offer forces liquidity before the five-year clock has run. The 60-day deadline is strict and cannot be extended.

How Deal Structure Changes the Bill

Stock Sale Versus Asset Sale

In a stock sale, you sell your shares directly. Your gain is proceeds minus basis, taxed at capital gains rates. This is the cleanest outcome for shareholders and the structure most founders 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 a liquidation, where each shareholder pays personal tax on the distribution. For a C corporation, that is double taxation. S corporations and LLCs generally avoid the entity-level layer, which makes asset sales less painful for those structures.

Earnouts and Escrow Holdbacks

Private deals frequently include contingent payments. Escrow holdbacks reserved for indemnification claims keep the same capital gains character as the rest of the proceeds. When funds are released from escrow, you report additional gain in the year you receive them.

Earnouts, where part of the price depends on hitting future revenue or performance targets, are messier. If the maximum earnout can be determined at closing, you may elect the installment method under Section 453 and spread gain across the years payments actually arrive. Each deferred payment may include imputed interest under Section 483 if any payments are due more than a year after the sale. That interest is taxed as ordinary income, not capital gains, and is calculated using the applicable federal rate at the time of the sale.⁵

Interest Charges on Large Installment Deals

Sellers using the installment method on bigger deals need to know about Section 453A. When the total face amount of installment obligations arising in a tax year exceeds $5 million, the seller must pay an interest charge to the IRS on the deferred tax liability each year the obligation remains outstanding.⁶ The rate tracks the IRS underpayment rate and fluctuates. On a large earnout, the government effectively charges you interest for the privilege of deferring the tax, and some sellers find it cheaper to recognize the gain upfront.

How You Got the Shares Changes the Tax

Founders and employees rarely bought their shares at full fair market value. The way the equity arrived determines both your basis and whether part of your proceeds is taxed at ordinary income rates rather than capital gains rates.

Non-Qualified Stock Options

With non-qualified stock options (NSOs), the tax event is at exercise. The spread between the stock’s fair market value on the exercise date and your exercise price is taxed as ordinary income and reported on your W-2.⁷ That ordinary income amount becomes your basis. Only gain above that basis is taxed as a capital gain when you sell, and the long-term holding period starts on the exercise date.

Incentive Stock Options

Incentive stock options (ISOs) look better on paper but carry a trap. There’s no regular income tax at grant or exercise, but the spread at exercise is an adjustment for the Alternative Minimum Tax, which can create a surprise bill in the exercise year before you’ve sold anything. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, with phaseouts beginning at $500,000 and $1,000,000 respectively.⁸ A large exercise can blow past the exemption easily.

To get the favorable treatment where the entire gain is long-term capital gain, you must hold the shares at least two years after the option grant date and at least one year after exercise.⁹ Selling before both periods are met triggers a disqualifying disposition, and the spread at exercise is reclassified as ordinary income. In a private company acquisition, timing around these periods is often impossible, which is why many ISO holders end up disqualified regardless of planning.

Restricted Stock Units and Restricted Stock Awards

Restricted stock units (RSUs) are simpler. The full fair market value of the shares on the vesting date is taxed as ordinary income and reported on your W-2. That value is your basis, and any gain or loss on a later sale is measured from the vesting date.¹⁰ If the sale happens shortly after vesting, there may be little additional gain.

Restricted stock awards (RSAs) default to the same treatment. But RSAs offer a planning tool RSUs do not. Under Section 83(b), you can elect to recognize ordinary income at the time of grant rather than at vesting. Make the election when the stock is worth almost nothing (as is common for early founders) and you pay a trivial amount of ordinary income tax upfront, start the capital gains clock immediately, and have all future appreciation taxed at capital gains rates when you eventually sell.

The 83(b) election must be filed with the IRS within 30 days of the grant using Form 15620, with a copy sent to the company.¹¹ Miss the 30-day deadline and it’s gone. No extension, no late procedure, no appeal.

If the Sale Is a Loss

Not every private company sale produces a profit. Normally a loss on stock is a capital loss, deductible only against capital gains plus up to $3,000 of ordinary income a year. Large losses then take years to use up.

Section 1244 changes that math. If the stock was originally issued by 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 a year ($100,000 for married couples filing jointly).¹² Ordinary losses offset all types of income without the $3,000 cap, which is a meaningful difference for founders whose startup failed but who have substantial W-2 or other income. The stock must have been issued directly to you for money or property, and you must be an individual taxpayer.

Estimated Tax Payments After a Big Sale

A private company sale typically produces a one-time spike that dwarfs your regular income. If you don’t make estimated payments to cover the 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. For higher-income taxpayers whose 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.¹³ In most sale situations, the 110% figure is the easiest safe harbor to hit, because last year’s liability was based on normal earnings.

If the sale closes late in the year, the annualized income installment method on Form 2210, Schedule AI, can reduce or eliminate penalties for earlier quarters by matching required payments to when the income was actually received.¹⁴

How to Report the Sale

Private company stock sales go on Form 8949, where you list each lot sold with its acquisition date, sale date, proceeds, and cost basis, classified as short- or long-term. Totals carry to Schedule D, which calculates net capital gain or loss for your Form 1040.¹⁵

Unlike publicly traded stock, private sales usually don’t generate a Form 1099-B. You’ll reconstruct basis and dates from stock purchase agreements, option exercise records, grant letters, and cap table records. Keep those documents permanently. In an audit, the burden is on you to prove basis and holding period.

A QSBS claim is reported on Form 8949 with a specific adjustment code. You’ll need documentation substantiating the five-year or three-year holding period, the company’s gross asset levels at the time of issuance, and compliance with the active business test throughout.¹⁶

Don’t Forget State Tax

State income tax adds a layer many sellers underestimate. Most states tax capital gains at the same rate as ordinary income, with the highest marginal rates running from zero in states with no income tax to above 13% in the highest-tax states. Your state of residence on the date of sale generally determines which state taxes the gain.

The federal QSBS exclusion does not automatically carry over to your state return. Many states don’t conform to Section 1202, which means you could owe state tax on the full gain even when your federal tax is zero. Sellers in non-conforming states sometimes find the state bill is their only tax on the transaction, which comes as a shock if they assumed the exclusion covered everything. Check conformity before closing.

If the company did business in states other than where you live, those states may try to tax a portion of the gain. The issue comes up more often in asset sales, where the business nexus is clearer, but some states take aggressive positions on stock sales as well. Sellers with potential multistate exposure should budget for the cost of filing non-resident returns and possibly contesting apportionment claims.

1
Internal Revenue Service. Topic No. 409, Capital Gains and Losses
2
Internal Revenue Service. Net Investment Income Tax
3
Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock
4
Office of the Law Revision Counsel. 26 USC 1045 – Rollover of Gain From Qualified Small Business Stock to Another Qualified Small Business Stock
5
Office of the Law Revision Counsel. 26 USC 483 – Interest on Certain Deferred Payments
6
Office of the Law Revision Counsel. 26 USC 453A – Special Rules for Nondealers
7
NASPP. Tax Withholding and Reporting for Equity Awards
8
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill
9
Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options
10
Morgan Stanley at Work. Restricted Stock, Performance Stock Awards and Taxes – What to Know
11
Internal Revenue Service. Form 15620, Section 83(b) Election
12
Office of the Law Revision Counsel. 26 USC 1244 – Losses on Small Business Stock
13
Internal Revenue Service. 2026 Form 1040-ES, Estimated Tax for Individuals
14
Internal Revenue Service. Instructions for Form 2210
15
Internal Revenue Service. About Form 8949, Sales and Other Dispositions of Capital Assets
16
Internal Revenue Service. 2025 Instructions for Form 8949 – Sales and Other Dispositions of Capital Assets