Concentrated Stock Tax Calculator (2026)

The first question every executive asks before selling employer stock: how much will I actually keep? This calculator computes after-tax proceeds on a concentrated stock sale — federal capital gains tax correctly stacked on top of your other income, the 3.8% NIIT surtax, and state capital gains tax for CA, NY/NYC, WA, TX, FL, and custom rates. Uses 2026 IRS-verified thresholds.

Why the effective rate is almost never 15%

Federal long-term capital gains are taxed at 0%, 15%, or 20% — but the rate that applies to your gain depends on where your total taxable income falls, not the gain alone. The key principle: capital gains stack on top of ordinary income in the bracket calculation. If your W-2 income already puts you well above $613,700 (MFJ) before you sell a single share, every dollar of LTCG is taxed at 20%. Add the 3.8% NIIT and state tax, and the real combined rate for a California executive is typically 37–38%.

2026 LTCG thresholds (total taxable income including the gain):

Most executives selling a concentrated position are well above the 20% ceiling before the stock sale is even counted. The 15% bracket window is essentially unavailable to someone with $400K+ in W-2 income.

The 3.8% NIIT: the surcharge most executives don't anticipate

The Net Investment Income Tax (IRC §1411) adds 3.8% to investment income — including capital gains — for taxpayers whose modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly).¹ For any executive selling a concentrated position, total MAGI will exceed this threshold, so the full gain is subject to NIIT. The combined federal rate on long-term gains becomes 23.8% (20% + 3.8%) — not 20%. The NIIT thresholds have not been adjusted for inflation since 2013, meaning more taxpayers are caught each year.

State tax: the variable that changes the outcome most

For a $10M sale, the difference between states can exceed $1.3M in tax:

• California (13.3%): Taxes capital gains at ordinary income rates — no preferential LTCG rate. Top rate is 12.3% plus a 1% Mental Health Services Tax, reaching 13.3% for income over $1 million. A CFO selling $10M in stock at a 13.3% state rate pays $1.33M more than a CFO in Texas.
• New York + NYC (9.65% + 3.88%): NY state taxes LTCGs at ordinary income rates (9.65% for income $1M–$25M). NYC residents add 3.876% local tax, bringing the combined rate to ~13.53% at executive income levels.
• Washington State (7% / 9.9% tiered): WA capital gains tax applies only to long-term capital gains over a $278,000 annual standard deduction. The rate is 7% on the first $722,000 above the deduction ($278K–$1M of gains), then 9.9% on gains above $1M. WA has no ordinary income tax; short-term gains are not subject to the WA CGT.
• Texas, Florida, Nevada, Wyoming, South Dakota (0%): No state income or capital gains tax. The after-tax advantage over California on a $10M sale is approximately $1.3M.

Strategies to reduce the tax bill on a concentrated position

If the calculator output looks painful, these are the tools available to executives:

• 10b5-1 planned sell-down: Spread sales over 2–4 years, which can keep some gains in a lower bracket during lower-income years (transition years, early retirement). Required anyway for Rule 144 compliance.
• Exchange fund (IRC §721): Contribute shares to a partnership fund and receive a diversified interest — no current tax event. 7-year lockup required; $2M+ minimums typical. Effective rate: 0% at contribution.
• Direct indexing completion portfolio: A separately managed account harvests losses across a basket of stocks to offset concentrated-position gains over 3–5 years.
• Charitable giving (DAF or CRUT): Donating appreciated shares to a donor-advised fund eliminates the capital gain entirely and generates an FMV deduction (30% AGI limit). For charitably inclined executives, this is the most tax-efficient exit.
• Zero-cost collar or variable prepaid forward: Economic diversification without an immediate sale, subject to §1259 constructive sale analysis if the collar is too tight.
• Qualified Opportunity Zone deferral: Roll recognized gains into a QOZ fund within 180 days to defer — and potentially exclude appreciation — under IRC §1400Z-2.

Section 16 and Rule 144: why executives can't just "sell it all"

Selling a large block of employer stock involves compliance constraints that don't apply to ordinary investors:

• Rule 144 volume limits: Affiliate sellers (officers, directors, 10%+ shareholders) may sell no more than the greater of 1% of outstanding shares or the 4-week average weekly trading volume per 90-day period. For a mid-cap company, selling a $10M position can take 12–24 months under Rule 144.
• Section 16(b) short-swing profits: Any purchase and sale within a 6-month window creates a recoverable "short-swing profit" — regardless of whether you had MNPI. Plan any sale timing around your recent purchase history.
• Blackout windows: Company policy prohibits trading during the ~3 weeks before earnings release through 2 business days after — four times per year, accounting for 4+ months of restricted trading.
• 10b5-1 plan requirement: Virtually all planned sales by executive officers must be pre-arranged under a Rule 10b5-1 plan, with a 120-day cooling-off period between plan adoption and first trade under the 2022 SEC amendments.

These constraints mean most executives can't exit a concentrated position in a single tax year even if they wanted to. The multi-year spread that Rule 144 and blackout windows impose often has a silver lining: smoother income, potentially lower blended rates.