Incentive Stock Options (ISOs) are one of the most common forms of equity compensation — and one of the most misunderstood when it comes to taxes.
- ISOs are a great form of compensation with very little risk and significant potential upside
- ISOs differ from regular stock options in how they're treated at time of sale (qualifying vs. disqualifying dispositions)
- Exercising ISOs may trigger the Alternative Minimum Tax
- Planning when to exercise can save you thousands — use our ISO Planner to find your optimal window
Stock Options — The Basics
Before diving into ISOs specifically, here's the core terminology you'll need:
- An Option is a promise that grants you the right to Exercise (buy) a stock at an agreed-upon price in the future. That price is called the Strike Price.
- Exercising an Option means paying money to convert the option into an actual share of stock you own. The date you do this is your Exercise Date.
- The Fair Market Value (FMV) is what the stock would sell for on the open market. When you exercise an ISO, the FMV is recorded even if the company isn't yet public.
- After exercising, you can sell the resulting stock at any time. The price you sell at is the Sale Price.
ISO-Specific Terminology
Grants / Awards
ISOs are typically received as part of a compensation package. The batch of ISOs promised to you is called an Equity Grant or Award. Each grant comes with a set strike price and a Grant Date — the date the grant is legally assigned to you. You can receive multiple grants over your tenure, each with different dates and potentially different strike prices.
Vesting
Vesting is the process by which options actually become yours. Even if you have a grant, the options aren't yours until they vest. Typical vesting schedules run 3–5 years to incentivize employees to stay.
A common structure is a 4-year schedule with a 1-year cliff — meaning no options vest in your first year, but after 12 months a chunk vests all at once, and then the rest vest quarterly or monthly after that.
The date a set of options vests is your Vesting Date. Your company's equity platform (Carta, Fidelity, Schwab, etc.) will track all of this for you.
Tax Implications of ISOs
When you exercise an ISO, you need to report it at tax time. Beyond regular income tax, exercising ISOs is one of the few things that can trigger the Alternative Minimum Tax (AMT) — a separate parallel tax system that runs alongside your regular taxes. You only pay AMT if it exceeds your regular income tax, but ISO exercises are one of the most common reasons it does.
Although you aren't taxed immediately at exercise, you will effectively be taxed twice on an ISO: once when you exercise (via potential AMT), and again when you sell the resulting stock (as a capital gain).
This isn't as unfair as it sounds — it works similarly to income tax on wages plus capital gains on investments. There's just a different calculation involved.
There's More: Qualifying vs. Disqualifying Dispositions
When you eventually sell the stock from an ISO exercise, the tax treatment depends on when you sell relative to when you exercised and when the grant was awarded. Read about qualifying vs. disqualifying dispositions to understand how timing affects your tax rate.