When you exercise non-qualified stock options, the difference between your strike price and the stock’s fair market value that day is taxed as ordinary income, and it’s also subject to Social Security and Medicare tax. That single moment is where most of the tax on NSO stock options happens. Any further gain after you exercise is a separate capital gain when you eventually sell the shares. Nothing is taxed when the options are granted, and nothing is taxed when they vest.
When the Tax Actually Hits
NSOs fall under Section 83 of the Internal Revenue Code, which governs property transferred in exchange for services.1Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services The grant itself isn’t a taxable event. Vesting isn’t either, on its own. The taxable moment is exercise, because that’s when you acquire shares that are no longer subject to a substantial risk of forfeiture.
So the tax picture for a typical NSO runs in two stages. Stage one is exercise: you pay your strike price, you receive shares, and the spread between what you paid and what the shares are worth becomes ordinary income for that tax year. Stage two is sale: whatever the shares do between exercise and sale is capital gain or loss, measured from a cost basis that includes both the strike price and the spread you already paid tax on.
How the Spread Is Taxed at Exercise
The spread is ordinary income, taxed at the same federal rates as your salary. If your strike price is $5 and the stock is trading at $25 on the day you exercise, you have $20 per share of ordinary income. That’s true whether you sell the shares immediately or hold them.
Your employer reports the income on your W-2 in Box 1 as wages and again in Box 12 with Code V, which specifically identifies NSO exercise income.2Internal Revenue Service. Announcement 2002-108 – Reporting of Nonstatutory Stock Option Income If you exercised as a non-employee (consultant, advisor, board member), the income shows up on Form 1099-NEC instead. NSOs are the only common form of equity compensation available to non-employees, which is why companies use them for anyone outside the W-2 workforce.
Federal rates for 2026 run from 10% to 37%. A single filer reaches the top bracket at $640,600 in taxable income; married couples filing jointly reach it at $768,700.3Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026 A large exercise can move you into a higher bracket for the year on its own, which is why people with long option terms sometimes split exercises across multiple years to soften the bracket impact.
Social Security and Medicare on the Spread
The spread is wages, so it’s also subject to FICA. Social Security tax runs at 6.2% up to the annual wage base, which is $184,500 for 2026.4Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax5Social Security Administration. Contribution and Benefit Base If your regular wages have already crossed that cap by the time you exercise, no more Social Security tax applies.
Medicare is 1.45% on all wages with no cap. An Additional Medicare Tax of 0.9% applies once your wages exceed $200,000 for single filers or $250,000 for married filing jointly.4Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax Employers withhold the extra 0.9% once your wages in the calendar year pass $200,000, regardless of your filing status. If that withholding doesn’t line up with what you actually owe, you reconcile on your return.
Most states tax the spread as ordinary income too, at rates ranging from zero in no-income-tax states to over 13% in the highest-tax states. If you moved during the year, or if you live in one state and work in another, allocating NSO income between states gets complicated quickly and usually deserves a conversation with a tax preparer.
Withholding Is Rarely Enough
Employers withhold federal income tax on the spread at the flat supplemental wage rate, which is 22% for most people and 37% on supplemental wages above $1 million in a year. If your marginal rate is 32% or 35%, the 22% flat withholding leaves a gap. That gap becomes a balance due at filing, and if it’s large enough, an underpayment penalty on top.
Anyone exercising a meaningful NSO grant should look at estimated tax payments for the quarter of the exercise rather than assuming payroll withholding covered it.
Capital Gains When You Sell the Shares
Once you exercise and hold the shares, everything from that point forward runs on capital gains rules. The holding period starts the day you exercise. Sell within one year, and the gain is short-term, taxed at ordinary income rates. Hold longer than a year, and you qualify for long-term capital gains rates of 0%, 15%, or 20%, depending on your taxable income.6Internal Revenue Service. Topic No. 409, Capital Gains and Losses
High earners face an additional 3.8% Net Investment Income Tax on capital gains once modified adjusted gross income exceeds $200,000 (single) or $250,000 (married filing jointly).7Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax The NIIT doesn’t apply to the exercise spread, since that’s wage income, but it does apply to the gain when you sell. For someone in the top brackets, that pushes the federal rate on post-exercise gains to 23.8%.
The Cost Basis Trap That Costs People Real Money
Your cost basis in the shares is the strike price plus the spread that was already taxed as wages. Exercise 100 shares at $10 when the stock is worth $50, and your basis is $5,000, not $1,000. The $4,000 spread already went through your W-2.
Here’s where the mistake happens. For NSOs granted after 2013, brokerages are not permitted to adjust the reported cost basis upward to include the wage income.8Internal Revenue Service. Instructions for Form 1099-B (2026) The Form 1099-B you get when you sell will typically show basis of only $1,000, the cash you paid. If you copy that number onto your return without an adjustment, you pay capital gains tax on the $4,000 you already paid ordinary income tax on. The same dollars get taxed twice.
The fix is an adjustment on Form 8949 that increases your reported basis to reflect the compensation income. Keep your W-2 showing Box 12 Code V, plus the exercise confirmation statement, together with your tax records. Trying to rebuild the correct basis years later, after a job change or a broker change, is painful and sometimes impossible.
Section 83(b) and Early Exercise
Some companies let you exercise options before they vest. The shares you receive stay subject to a repurchase right — if you leave before vesting, the company buys them back, usually at your strike price. Without any special election, early exercise doesn’t help you tax-wise: Section 83 still treats each batch of shares as taxable when its vesting condition lapses, using the fair market value on that later date.
A Section 83(b) election flips this. By filing the election within 30 days of the early exercise, you choose to recognize the entire spread as ordinary income right then, at the transfer date, instead of piece by piece as the shares vest.1Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services When you early-exercise at a moment when the strike price equals fair market value, the spread is near zero and the current tax bill is minimal. From that point forward, all appreciation is capital gain, and the long-term holding clock runs from the exercise date rather than each vesting date.
You file by submitting IRS Form 15620 to the IRS office where you file your return, and you must also give a copy to the company.9Internal Revenue Service. Form 15620, Section 83(b) Election The 30-day deadline is absolute. Miss it, and the election is gone. It’s also irrevocable. If the company fails, or you leave before vesting and the shares get repurchased, you cannot recover the taxes you already paid. That’s the trade: certainty of capital gains treatment on future appreciation, in exchange for paying tax now on value that might never materialize.
Section 409A and the Strike Price Problem
The strike price on an NSO has to be at least fair market value on the grant date. If it’s lower, the option gets treated as deferred compensation under Section 409A, and the consequences land on the option holder, not the company: all vested amounts become immediately taxable, a 20% additional tax applies on top of regular income tax, and a premium interest charge runs back to the vesting date.
For public companies the strike price question is easy. For private companies, the standard defense is a 409A valuation, an independent appraisal that establishes fair market value. Using an independent appraiser creates a safe harbor: the IRS bears the burden of showing the value was unreasonable, rather than the company having to prove it was reasonable. Most venture-backed companies refresh their valuations annually or after material events like a funding round.
If you’re receiving NSOs from a private company, ask when the last 409A valuation was completed. A stale valuation, meaning one older than 12 months or one that predates a significant business event, raises the risk that the strike price doesn’t reflect current fair market value. And when that risk becomes a real 409A problem, it becomes a problem on your tax return.
The Exercise-and-Hold Tax Trap
The single most damaging pattern with NSOs is exercising when the stock is high, holding for long-term capital gains treatment, and watching the stock fall. You exercise at $50, owe ordinary income tax on the full spread, and then the stock slides to $15. The tax bill is fixed at the $50 valuation. The shares that were supposed to pay it are worth a fraction of that. This has wiped out employees at both startups and public companies during market downturns.
Two habits help. Sell enough shares at exercise to cover the tax bill in cash, even if you plan to hold the rest. And when you’re deciding how much to exercise in a given year, look at the total tax hit against your ability to write that check without needing the shares themselves to pay for it.
Private-Company NSOs Carry Extra Risk
For private-company options, add liquidity risk on top of the tax picture. You may exercise, owe taxes on the spread that year, and hold shares you can’t sell for years, if ever. There’s no public market. Secondary sales may be blocked by the company’s bylaws or subject to a right of first refusal. An IPO or acquisition is never guaranteed. Before exercising private-company NSOs, add up the full cash outlay — strike price plus estimated federal, state, and FICA taxes — and decide whether you can afford to lose that amount entirely if the shares never become liquid.