A right to buy shares later at a fixed price (the strike price). Options typically vest over four years with a one-year cliff. Common for employees; you don't own shares until you exercise.
stock option
/stɒk ˈɒpʃən/ noun — A contractual right granted to an employee, advisor, or contractor to purchase a specified number of shares of company stock at a fixed price (the strike price or exercise price) during a defined window. Stock options are not shares themselves; they are rights that must be exercised — by paying the strike price — to become actual equity ownership.
Why it matters
Stock options are the primary tool for equity compensation beyond the founding team. They allow startups to attract talent by offering a share of future upside without requiring the employee to immediately purchase shares or the company to issue shares before they're earned.
Understanding how options work is essential whether you're granting them or receiving them. The difference between ISOs and NSOs, the timing of exercise decisions, and the 90-day window after departure can mean thousands of dollars in tax savings or losses.
For founders, understanding the option pool and how it affects dilution is equally important. The option pool is typically established before a funding round, which dilutes existing shareholders before the investment closes — a dynamic that changes the effective pre-money valuation from a founder's perspective.
How it works
A stock option gives you the right to buy a specific number of shares at a fixed price (the strike price) set at the time of grant. Options typically vest over four years with a one-year cliff — nothing vests during the first year, 25% vests on the one-year anniversary, then the remaining 75% vests monthly over the next three years.
There are two main types. ISOs (Incentive Stock Options) get favorable tax treatment if holding requirements are met, but are only available to employees and are capped at $100,000 in exercisable value per year. NSOs (Non-Qualified Stock Options) can go to anyone — employees, consultants, advisors — but the spread between strike price and fair market value at exercise is taxed as ordinary income.
You don't own any shares until you exercise, which means paying the strike price multiplied by the number of options you're exercising. If you leave the company, you typically have 90 days to exercise vested options or they expire worthless. Some employee-friendly companies offer extended windows of 5-10 years.
Early exercise — exercising options before or shortly after they vest — can be advantageous when combined with an 83(b) election. This starts your capital gains holding period early and locks in a low taxable spread while the company is still worth little.
ISOs vs. NSOs compared
| Feature | ISO | NSO |
|---|---|---|
| Who can receive | Employees only | Anyone (employees, advisors, contractors) |
| Annual limit | $100,000 exercisable per year | No limit |
| Tax at exercise | No regular income tax (potential AMT) | Spread taxed as ordinary income |
| Qualifying disposition | Hold 1yr from exercise + 2yrs from grant for LTCG | LTCG only applies to gain after exercise |
| Best for | Employees expecting significant company growth | Advisors, contractors, or grants exceeding ISO limits |
History and origin
Stock options as a form of employee compensation date to the 1950s, when Congress created the ISO structure to encourage executive retention at public companies. The preferential tax treatment was designed to align employee incentives with long-term shareholder value by rewarding those who held shares for extended periods.
Options became the dominant form of startup equity compensation in Silicon Valley during the 1980s and 1990s as tech companies needed to compete with established firms for engineering talent without being able to offer equivalent cash salaries. Companies like Fairchild Semiconductor, Intel, and Apple granted options broadly across their employee base — a practice that was unusual in other industries, where options were typically reserved for senior executives.
The dot-com era made stock options famous and, for many employees, extremely lucrative. Post-bubble accounting rule changes (FAS 123R in 2004) required companies to expense options on their income statements for the first time, prompting some public companies to shift toward Restricted Stock Units (RSUs). However, options remain the standard tool at private startups because RSUs create an immediate tax liability upon vesting that is difficult to pay when shares cannot be sold.
Frequently asked questions
What is the difference between ISOs and NSOs?
ISOs (Incentive Stock Options) are only available to employees, have a $100,000 annual exercisable limit, and can qualify for preferential capital gains tax treatment. NSOs (Non-Qualified Stock Options) can be granted to anyone, have no annual limit, and the spread at exercise is taxed as ordinary income regardless of how long you hold the shares afterward.
When should I exercise my stock options?
Exercising early — ideally when the strike price is close to fair market value — minimizes taxes and starts your long-term capital gains holding period. An early exercise with an 83(b) election means you pay taxes on a minimal spread at grant rather than a large spread later. Later exercise, when the company is worth more, results in higher ordinary income taxes for NSOs or potential AMT exposure for ISOs.
What happens to my options if I leave the company?
Standard option agreements give you 90 days from your last day to exercise vested options. After that window, vested options expire. Unvested options are always forfeited at departure. Some companies extend the exercise window to 5 or 10 years — a much more employee-friendly policy. Always check your option agreement before resigning.
What does it mean to exercise stock options?
Exercising your options means paying the strike price per share to convert your option rights into actual shares of stock. If you have options on 10,000 shares at a $0.50 strike price, exercising costs $5,000 and gives you 10,000 shares of common stock. You don't own shares — or participate in an exit — until you exercise.
What is a stock option pool?
An option pool is a reserved block of shares set aside for future grants to employees, advisors, and contractors. Investors usually require the option pool to be set — and sometimes enlarged — before their investment closes, which dilutes existing shareholders before the round rather than after.
How are stock options taxed?
For NSOs: the spread between strike price and fair market value at exercise is taxed as ordinary income. For ISOs: if you hold shares at least one year from exercise and two years from grant, gains qualify for long-term capital gains rates — a significant advantage. Early exercise with an 83(b) election can dramatically reduce the taxable spread for both types.
How many stock options should an early employee receive?
Equity grants vary by stage and role. At seed stage, a VP-level hire might receive 0.25-1%. An engineer at Series A might receive 0.1-0.25%. Earlier employees generally receive larger grants to compensate for higher risk. Grants are typically expressed as a number of shares or as a percentage of the fully diluted share count.
Learn more
- Types of startup equity: common stock, options, SAFEs, and more
- 83(b) election explained: how to save on taxes when you exercise early
- Vesting explained: cliffs, acceleration, and the schedule that protects everyone
- How much equity should you give startup advisors?
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