网络学习后的总结，理解不当请原谅，仅供参考。
For example, $10 stock option grant price for 2000 shares, vesting in 4 years.
Grant date: generally no tax implications.
Exercise date: normally upon termination of employment. Say after 3 year of grant date. Buy $10 x 1500 vested shares. Company will issue Form 3921 to show grant price $10, fair value on exercise date (say $30), and 1500 shares exercised.
No ordinary income tax but employee will need to calculate the AMT (alternative minimum tax) based on the difference between fair value $30 and cost $10 times 1500 shares x AMT tax rate. The cost basis of these stock option AMT will be $30 per share in the future.
Selling date: say selling these 1500 shares after IPO at $210. Capital gain = ($210 - $10)x1500 = $300,000; AMT based on ($210 - $30 ) x 1500 x AMT tax rate. Broker will issue Form 1099-B.
由于AMT, Exercise stock option 也有税务风险。在2000年网络股票泡沫期间，有员工获$1 x 50,000公司股权，在上市前估值到一股$100（409A fair value)时Execise换为股票，缴了几十万的AMT，不料上巿后不久公司股价大跌成仙股。白白打工几年缴了AMT。狼会吃肉，也会挨揍！
