Not All Options Are Created Equal
When a company grants you stock options, the offer letter specifies one of two types: ISOs (Incentive Stock Options) or NSOs (Non-Qualified Stock Options). The difference is entirely about when and how the IRS taxes you — and it can mean a difference of hundreds of thousands of dollars on the same underlying equity.
NSO — Non-Qualified Stock Options
NSOs are the simpler type. When you exercise an NSO (i.e., pay the strike price to buy the shares), the IRS immediately treats the "spread" — the difference between the current fair market value and your strike price — as ordinary income.
- Tax event: At exercise.
- Tax rate: Ordinary income rates. In 2024, the federal top bracket is 37%. Add California state income tax (up to 13.3%) and you can face a combined marginal rate above 50%.
- Mechanics: The spread is added to your W-2. Your employer withholds taxes just like salary. You owe the tax whether or not you sell the shares.
Example: You exercise 10,000 NSOs with a $1 strike price when the FMV is $20. The spread is $190,000. At a 45% combined rate, you owe $85,500 in taxes — immediately — even if you hold the shares and they later drop to zero.
ISO — Incentive Stock Options
ISOs are the tax-advantaged type, available only to employees (not contractors). The key benefit: no regular income tax at exercise.
- Tax event (regular): At sale, not at exercise.
- Qualifying disposition: If you hold the shares for at least 1 year after exercise AND 2 years after the original grant date, all gains are taxed as Long-Term Capital Gains (LTCG) — currently 20% federal for high earners, versus 37% ordinary income. This is the ISO benefit.
- Disqualifying disposition: If you sell before meeting those holding periods, the spread is taxed as ordinary income — same as an NSO.
- The trap: ISOs trigger the Alternative Minimum Tax (AMT) at exercise. See the next concept.
Key Structural Difference:
NSOs can be granted to employees, contractors, and board members. ISOs can only be granted to employees, and there is an annual ISO exercise limit of $100,000 in value (based on grant-date FMV). Options above that limit automatically convert to NSOs.