By Harry Prabandham · Updated September 27, 2026
Equity Compensation
How Employee Stock Options Work: A Plain-English Primer
A stock option is the right to buy company shares at a fixed strike price. ISOs and NSOs are taxed differently, and ISOs can trigger AMT at exercise.
How Employee Stock Options Work: A Plain-English Primer
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What is an employee stock option?
- It is the right, not the obligation, to buy a set number of shares at a fixed strike price until an expiration date.
- The strike is usually the fair market value on the grant date, which for private companies comes from a 409A valuation.
- Options typically vest over time, often four years with a one-year cliff, and unvested options are usually forfeited if you leave.
- An option only has value if the share price rises above the strike, and exercising means paying the strike to own shares.
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Full Guide
What is an employee stock option?
- It is the right, not the obligation, to buy a set number of shares at a fixed strike price until an expiration date.
- The strike is usually the fair market value on the grant date, which for private companies comes from a 409A valuation.
- Options typically vest over time, often four years with a one-year cliff, and unvested options are usually forfeited if you leave.
- An option only has value if the share price rises above the strike, and exercising means paying the strike to own shares.
What is the difference between ISOs and NSOs?
- With NSOs, the spread at exercise is taxed as wages, with withholding and payroll taxes; later growth is capital gain or loss.
- With ISOs, exercise creates no regular income tax, but the spread counts for the alternative minimum tax.
- Selling ISO shares more than two years after grant and one year after exercise makes the whole gain over the strike long-term capital gain.
- Selling sooner is a disqualifying disposition: the exercise spread becomes ordinary income, though not subject to payroll taxes.
- ISOs go only to employees, and any ISOs over $100,000 of grant-date value first exercisable in one year are treated as NSOs.
When does the AMT come into play?
- For 2026, the AMT exemption is $90,100 single and $140,200 joint, phasing out 50 cents per dollar above $500,000 and $1,000,000 of AMT income.
- AMT rates are 26% and 28%, applied to a broader income base that includes the ISO spread.
- AMT caused by ISO exercises usually creates a credit that can be used in later years when regular tax is higher.
- California has its own AMT, so state exposure needs modeling too.
What happens to options when you leave the company?
- Many plans give 90 days after departure to exercise vested options before they expire.
- ISOs exercised more than three months after employment ends are taxed as NSOs.
- Some companies offer longer post-termination windows, but the extended options generally lose ISO status.
- Options usually expire ten years after grant, or five years for ISOs held by owners of more than 10% of the company.
What exercise approaches do people commonly consider?
- Early exercise with an 83(b) election, when allowed, while the spread is small or zero.
- Spreading ISO exercises across several years to stay near the point where AMT begins.
- Exercising and selling at the same time in an IPO, acquisition, or tender offer, which produces ordinary income.
- Holding shares after exercise adds concentration risk, and the price can fall below the value you paid tax on.
Key takeaways
- Know your grant type, strike, vesting schedule, expiration date, and post-termination window.
- NSOs create wage income at exercise; ISOs can create AMT at exercise and better treatment at sale if held long enough.
- The 2026 AMT phase-out changes make ISO modeling more important for high earners.
- Confirm tax projections with a CPA; Rubric does not prepare tax returns or give legal advice.
Related Topics
Equity Compensation
ISOs vs NSOs: How Stock Option Taxes Differ
NSO spreads are taxed as wages at exercise; ISO spreads skip regular tax but can trigger AMT, and qualify for long-term rates if holding periods are met.
Tax PlanningAlternative Minimum Tax (AMT) Planning
AMT is a parallel federal tax you pay when it exceeds regular tax. ISO exercises are the most common trigger; 2026 law changes widen its reach.
Equity CompensationLeaving a Startup With Stock Options: The Exercise Deadline
When you leave a company, vested options usually expire unless exercised within a set window, often 90 days, and ISOs lose tax status after three months.