Stock options are one of the most valuable — and most misunderstood — forms of compensation. Tech employees and startup workers often have significant equity on paper but make costly mistakes when it comes to exercising, timing, and taxes. Getting this wrong can mean paying taxes on money you never received, or missing opportunities worth hundreds of thousands of dollars.
Disclaimer: Tax rules around equity compensation are complex and vary by situation, state, and company. This article is educational. Consult a licensed tax professional or financial advisor before making decisions about stock options.
The Basic Concept
A stock option gives you the right (but not the obligation) to buy shares of your company's stock at a specific price — called the strike price or exercise price — regardless of what the stock is actually worth.
If you have options with a $10 strike price and the stock is worth $50, you can buy shares worth $50 for $10 each — a $40 per-share gain. If the stock never rises above $10, your options are "underwater" (worth nothing to exercise).
Key Terms
Grant: When the company awards you the options.
Strike price (exercise price): The price at which you can buy shares, fixed at grant.
Vesting: The schedule over which your options become exercisable. Typical: 4-year vesting with a 1-year cliff (0% vests until 12 months in, then 25%, then monthly/quarterly for remaining 3 years).
Cliff: The minimum time before any options vest at all.
Exercise: Using your options to purchase shares at the strike price.
Expiration: Options expire — typically 10 years from grant. If you leave the company, you usually have 30–90 days to exercise (sometimes less). Unexercised options expire worthless.
409A valuation: An independent appraisal of the company's fair market value per share (required for private companies). Determines the strike price for new grants.
ISO vs. NSO: The Tax Difference
The two types of employee stock options have dramatically different tax treatment:
Incentive Stock Options (ISOs):
- Only available to employees (not contractors or advisors)
- Limited to $100,000/year in options that can first become exercisable
- No ordinary income tax when exercised (if holding requirements are met)
- AMT (Alternative Minimum Tax) implications — the "spread" at exercise is an AMT preference item
- Qualifying disposition: If you hold shares for 2 years after grant AND 1 year after exercise, gains are taxed at long-term capital gains rates (15% or 20%)
- Disqualifying disposition: If you sell before the holding periods, ordinary income tax applies to the spread at exercise
Non-Qualified Stock Options (NSOs/NQSOs):
- Can be granted to employees, contractors, advisors, anyone
- The spread at exercise (market value minus strike price) is taxed as ordinary income in the year of exercise — regardless of whether you sell
- Employer withholds tax at exercise
- Post-exercise gains are capital gains (short or long-term depending on holding period)
The practical difference: ISOs are tax-advantaged but complex. NSOs are simpler but you owe ordinary income tax at exercise.
The Exercise Decision
Exercising options before a liquidity event (IPO, acquisition) is a high-stakes decision, especially for ISOs:
Early exercise: Some option agreements allow exercising unvested options (with an 83(b) election). This starts the holding period clock early, potentially converting future gains to long-term capital gains. Risk: the shares may be worthless if the company fails.
Waiting to exercise at IPO/acquisition: Simpler and less risky, but you'll owe more in taxes (shorter holding period = less favorable capital gains treatment for ISOs; larger spread = more ordinary income for NSOs).
Post-company-departure exercise window: If you leave, you typically have 30–90 days to exercise or lose your options. Some companies (notably Stripe and others) have extended this window to years for long-tenured employees. Know your terms.
The AMT Problem with ISOs
For ISOs, the spread at exercise (market value minus strike price) is not regular income but is an AMT preference item. If the spread is large, you may owe Alternative Minimum Tax in the exercise year — even if you haven't sold any shares.
Example: You exercise 10,000 ISOs with a $1 strike price when shares are worth $20. Regular income tax: $0. But you have $190,000 in AMT preferences. Depending on your other income, you may owe significant AMT.
The catastrophic scenario: exercise ISOs → company value drops → you owe AMT on a gain you can no longer realize. This destroyed many employees' finances in the 2000 dot-com bust.
Mitigation: Work with a CPA specializing in equity compensation before exercising any significant number of ISOs.
RSUs: The Simpler Alternative
Many later-stage and public companies grant Restricted Stock Units (RSUs) rather than options. RSUs are simpler:
- No exercise required — shares vest automatically
- No strike price, no exercise decision
- Taxed as ordinary income at vesting (on the full fair market value)
- After vesting, treated like any other company stock for capital gains purposes
RSUs have no "underwater" risk — options can expire worthless; RSUs are always worth something as long as the stock has value.
Questions to Ask Your Employer
When evaluating equity compensation:
- What percentage of the fully diluted company do my options represent?
- What is the current 409A valuation per share?
- What is the strike price on my options?
- What is the vesting schedule and cliff?
- How long is my exercise window if I leave?
- Are these ISOs or NSOs?
- What is the preference stack? (liquidation preferences determine how much exits proceed to common shareholders)
Equity compensation can be life-changing wealth or a complex tax problem, depending on how well you understand it. The time to learn is before you exercise — not after.