Employee Stock Option Plan: How Options Work, Vest, and Are Taxed

Employee stock options give you a contractual right to buy shares of your company at a fixed price, and how much money you keep depends on your vesting schedule, when you exercise, and which tax rules apply to your grant. The gap between your strike price and the market value of the stock is where the value sits. Taxes can eat a large piece of that gap if you don’t plan the timing.

Two grant types dominate: incentive stock options (ISOs), which can qualify for capital gains treatment but expose you to the alternative minimum tax, and non-qualified stock options (NQSOs), which are taxed as ordinary income the moment you exercise. Everything below flows from that split.

What an Employee Stock Option Actually Is

Your grant agreement is the contract, and every dollar decision starts with the numbers in it. The strike price (also called the grant price or exercise price) is what you pay per share when you exercise. The grant date is when the option was issued and starts the clock on vesting and tax holding periods. The expiration date is a hard deadline: if you haven’t exercised by then, the options disappear.

To see whether your options have value, subtract the strike price from the current fair market value. Options with a $15 strike price on a $50 stock carry $35 of intrinsic value each. If the stock trades below your strike price, the options are “underwater” and worth nothing to exercise; you’d be paying more per share than the market charges.

ISOs vs. NQSOs

The label on your grant drives the tax outcome. Read the grant agreement and confirm which type you hold before making any exercise decision.

Incentive stock options are governed by Section 422 of the Internal Revenue Code and can only be granted to employees, not consultants, advisors, or outside directors. The stock option plan must be approved by shareholders within 12 months before or after the board adopts it. There is also a $100,000 cap: if the fair market value of shares that first become exercisable in a single calendar year exceeds $100,000, the excess portion is treated as non-qualified.¹

Non-qualified stock options come with far fewer strings. Companies can grant them to employees, board members, contractors, and advisors, and the plan itself faces fewer administrative rules. The tradeoff is that NQSOs never qualify for the deferred tax treatment ISOs can.

Vesting: When You Actually Own the Right to Buy

A grant is not immediate ownership. Vesting is the process of earning the right to exercise, and companies use it to keep you around.

The most common schedule is four years with a one-year cliff. Nothing vests in the first twelve months. Leave before the cliff and you walk away with zero. At the one-year mark, 25% vests at once, and the remaining 75% usually vests in monthly or quarterly installments over the next three years. Monthly vesting means 1/48th of the total grant every month after the cliff.

Some companies use graded vesting without a cliff, so shares vest in equal installments from day one. Others tie vesting to performance milestones like revenue or product targets. Your grant agreement spells out the structure.

How to Exercise Your Options

Once options vest, you have several ways to actually buy the shares. The right choice depends on how much cash you have and whether you want to hold the stock or take the profit immediately.

Cash exercise. You pay the full strike price out of pocket. Exercising 1,000 shares at a $10 strike price costs $10,000. You end up owning all 1,000 shares outright.
Cashless exercise (same-day sale). Your broker sells all the shares immediately upon exercise, uses the proceeds to cover the strike price and fees, and deposits the balance in your account. You spend none of your own money and hold none of the stock.
Sell-to-cover. The broker sells only enough shares to cover the strike price, taxes, and fees, and you keep the rest. You end up holding stock without fronting cash.
Net exercise. The company itself withholds enough shares to cover the exercise price and delivers only the net shares to you. This is common at companies that want to limit dilution and avoids some securities-law issues for insiders since no market sale occurs.

Mechanically, most exercises run through a brokerage platform tied to your equity awards. You log in, pick the grant, enter the number of vested shares, choose the method, and confirm. Settlement generally takes a couple of business days.

How NQSOs Are Taxed

NQSOs create a tax event the day you exercise, whether or not you sell the shares. The spread between the strike price and the fair market value on the exercise date is ordinary income reported on your W-2.² Strike price of $10 on a $30 stock means $20 per share of ordinary income. On 1,000 shares, that is $20,000 added to your taxable wages for the year.

Your employer withholds on that income before you see it. The federal supplemental wage withholding rate is 22% on amounts up to $1 million and 37% above that.³ You also owe Social Security tax at 6.2% up to the annual wage base and Medicare at 1.45% with no cap. Combined withholding on the spread often lands around 30% or more before state taxes. The spread shows up on your W-2 in Box 12 under Code V.⁴

If you hold the shares after exercising and sell later at a higher price, the extra gain is a capital gain. Sell within a year and it is short-term (ordinary rates). Hold more than a year and it qualifies for long-term capital gains rates.

How ISOs Are Taxed

ISOs get better treatment under the regular tax system, and worse traps if you miss the holding rules.

When you exercise ISOs, no regular federal income tax is due on the spread. Nothing is withheld and nothing appears on your W-2 at exercise.² To lock in long-term capital gains treatment when you eventually sell, you must hold the shares at least two years from the grant date and at least one year from the exercise date.¹ Meet both and the entire profit from strike price to sale price is taxed at long-term capital gains rates (0%, 15%, or 20% depending on your income).

Sell before hitting either holding period and the transaction becomes a disqualifying disposition. The spread at exercise gets reclassified as ordinary income and you lose the capital gains benefit.⁵ Exercising in December and selling in January feels like a long hold, but it satisfies neither requirement.

Your employer files Form 3921 when you exercise ISOs, reporting the exercise date, fair market value, strike price, and number of shares. You receive a copy and use the information when preparing your return; you do not file the form yourself.⁶

The AMT Trap on ISO Exercises

This is the part that blindsides people. Even though you owe no regular income tax when you exercise ISOs, the spread counts as income for the Alternative Minimum Tax.² If the spread is large enough to push your AMT calculation above your regular tax liability, you owe the difference.

The AMT runs as a parallel calculation. You compute your regular tax, then recompute under AMT rules (which add back certain deductions and include the ISO spread), and pay whichever is higher. For 2026, the AMT exemption is $90,100 for single filers and $140,200 for married couples filing jointly, phasing out at $500,000 and $1,000,000 of AMT income respectively.⁷

An example makes the size of the problem clear. Exercise 10,000 ISOs with a $5 strike price when the stock is worth $25. That $200,000 spread produces zero regular income tax. It gets added to your AMT income. A single filer with $150,000 of regular income now sits at $350,000 of AMT income, well above the exemption, and the AMT bill can easily reach five figures.

AMT paid on ISO exercises generates a minimum tax credit you can carry forward and apply against regular tax in future years.⁸ The credit does not help the year you pay the AMT, but it softens the total cost over time. Running an AMT projection before exercising is the single best move to avoid a surprise.

Early Exercise and the 83(b) Election

Some companies, particularly startups, let you exercise options before they vest. Early exercise creates a tax-planning opportunity with a strict 30-day deadline.

When you early-exercise unvested shares, the stock you get is still subject to the vesting schedule. Leave before vesting and the company can repurchase the unvested shares at your original strike price. Under default tax rules you would owe tax as each tranche vests, on the spread between the strike price and the fair market value at that later vesting date. At a fast-growing startup, that spread can be enormous by the time later tranches vest.

A Section 83(b) election lets you flip that. Filing this election means you pay tax on the spread at the time of exercise instead of waiting for each vesting date.⁹ Exercise early when the fair market value equals or is close to the strike price and the taxable spread is small or zero. All future appreciation is then capital gain when you sell.

The catch: you must file the election with the IRS within 30 days of receiving the shares, and you cannot revoke it.⁹ The IRS offers Form 15620 for this purpose.¹⁰ Miss the deadline or watch the stock later fall below what you paid and you are stuck. You have already paid tax on value you may never realize, and if you forfeit unvested shares you get no deduction for the loss.

What Happens to Your Options When You Leave

Quitting, being laid off, and being fired all affect your options, and the timeline is tighter than most people expect.

Unvested options are almost always forfeited on your last day. They go back to the company. Vested options survive your departure but only for a limited window called the post-termination exercise period. Ninety days is the most common window, though some companies extend it to six months, a year, or longer. Your grant agreement states the exact period. Miss it and vested options expire worthless no matter how much intrinsic value they carry.

That creates a real squeeze for ISO holders. Exercising after leaving can trigger AMT liability without an easy way to sell the shares and cover the bill, especially at a private company. Some departing employees face a choice between writing a large check or walking away from equity they spent years earning.

If your company gets acquired, unvested options depend on the deal structure and your grant agreement. Double-trigger acceleration is the most common employee protection: unvested options vest fully only when two events both happen, the company is sold and you are involuntarily terminated (or your role changes materially) within a set period after closing, typically 9 to 18 months. Termination for cause usually doesn’t count. If the acquirer refuses to assume the option grants at all, the acceleration language in your agreement becomes critical.

Extra Considerations at Private Companies

Private-company options raise practical problems public-company employees never face. The biggest is illiquidity: you cannot easily sell shares you have exercised because there is no public market.

409A Valuations and Your Strike Price

Private companies must get an independent valuation (commonly called a 409A valuation) to set the fair market value before granting options. Your strike price must be at or above that value. If the company sets the strike below fair market value, the consequences fall on you: the options can be treated as deferred compensation subject to immediate income inclusion, a 20% additional tax, and interest charges.¹¹

The IRS treats a 409A valuation as valid for up to 12 months, unless a material event like a new funding round changes the value in the interim. Joining right before a large round can mean the strike price on options granted soon after will jump.

Selling Shares Before an Exit

Shares acquired through option exercises at private companies are typically restricted securities that cannot be freely traded.¹² Companies often impose additional transfer restrictions, including rights of first refusal that require you to offer shares back before selling to anyone else. Some companies run periodic tender offers or liquidity events, but those are at the company’s discretion.

Secondary markets exist for shares of some well-known private companies, but participating usually requires company approval and compliance with federal securities exemptions. Many private-company employees exercise and then wait months or years for an IPO or acquisition. That waiting period means tying up cash and potentially owing taxes with no guaranteed return.

Section 83(i) Deferral

Employees at qualifying private companies may be able to defer income tax on exercised options for up to five years under Section 83(i).⁹ The election is due within 30 days of the date your rights in the stock become transferable or are no longer subject to a substantial risk of forfeiture.

Eligibility is narrow. The company must have no publicly traded stock and must maintain a written plan granting options or RSUs to at least 80% of its U.S. employees with the same rights and privileges.⁹ You are disqualified if you are or ever have been the CEO, CFO, a 1% owner, or one of the four highest-paid officers.¹³ Few companies and employees meet all the conditions, but where they do the deferral can be valuable.

Other Tax Rules That Can Bite

The Wash Sale Rule

Sell company stock at a loss and then exercise options on the same stock (or buy shares in the open market) within 30 days before or after the sale and the IRS disallows the loss under the wash sale rule.¹⁴ The disallowed loss is added to the cost basis of the new shares, so it is not lost forever, but you cannot use it against gains this year. To avoid a wash sale, wait at least 31 days between the loss sale and any reacquisition, including through exercise.

The 3.8% Net Investment Income Tax

Capital gains from selling shares acquired through options may be subject to an additional 3.8% net investment income tax if your modified adjusted gross income exceeds $200,000 for single filers or $250,000 for married couples filing jointly.¹⁵ These thresholds are not inflation-adjusted, so more taxpayers cross them each year. A large ISO qualifying disposition or a significant NQSO exercise that pushes income above these levels can trigger the surtax on top of your capital gains rate.

State Taxes

State treatment of stock options varies widely. A few states impose no income tax at all. Some follow federal treatment closely. Others do not recognize the favorable capital gains treatment the federal code allows for qualifying ISO dispositions, meaning you could owe state tax at ordinary rates on a sale that qualifies for long-term federal capital gains. Move between states while holding options and the income allocation adds another layer. When the amounts are meaningful, a tax professional familiar with your state’s rules is worth the cost.

1
Office of the Law Revision Counsel. 26 USC 422 – Incentive Stock Options
2
Internal Revenue Service. Topic No. 427, Stock Options
3
Internal Revenue Service. 2026 Publication 15-T
4
Internal Revenue Service. Announcement 2002-108
5
Office of the Law Revision Counsel. 26 USC 421 – General Rules
6
Internal Revenue Service. Instructions for Forms 3921 and 3922
7
Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026
8
Internal Revenue Service. Topic No. 556, Alternative Minimum Tax
9
Office of the Law Revision Counsel. 26 USC 83 – Property Transferred in Connection With Performance of Services
10
Internal Revenue Service. Form 15620, Section 83(b) Election
11
Office of the Law Revision Counsel. 26 USC 409A – Inclusion in Gross Income of Deferred Compensation Under Nonqualified Deferred Compensation Plans
12
U.S. Securities and Exchange Commission. What Is a Private Secondary Market?
13
Internal Revenue Service. Guidance on the Application of Section 83(i)
14
Office of the Law Revision Counsel. 26 USC 1091 – Loss From Wash Sales of Stock or Securities
15
Congressional Research Service. The 3.8% Net Investment Income Tax: Overview, Data, and Policy Options