Exercising Stock Options

The act of purchasing shares at your option's strike price — a decision with significant tax, timing, and financial implications that most option-holders don't fully understand until they're in the moment.

Exercising a stock option means using your right to purchase company stock at the pre-agreed strike price (also called the grant price or exercise price) established when the option was granted. If you have options to buy 1,000 shares at a $10 strike price and the current fair market value is $30, exercising those options lets you buy at $10, giving you $20/share of spread (or 'intrinsic value'). Options must be exercised after they vest and before they expire — most stock option plans have a 10-year expiration window from the grant date, and a 90-day post-termination exercise window (meaning if you leave the company, you typically have only 90 days to exercise before the options lapse).

The tax treatment of exercising stock options depends critically on whether you have Incentive Stock Options (ISOs) or Non-Qualified Stock Options (NSOs/NQSOs). NSOs are simpler: the spread at exercise is ordinary income taxed in the year you exercise, and the company withholds taxes at that point. ISOs are more tax-favorable in theory — there's no ordinary income tax at exercise if you hold the shares long enough — but exercising ISOs creates a tax preference item that may trigger Alternative Minimum Tax (AMT), a parallel tax system that catches ISO exercises as a taxable event even though regular income tax doesn't apply. This ISO/AMT interaction is one of the most confusing and financially consequential elements of equity compensation and has resulted in large, unexpected tax bills for employees at companies that later declined in value.

The timing of exercise involves weighing several factors: expected stock price appreciation, tax efficiency (ISO holding periods, AMT exposure, long-term vs. short-term capital gains), liquidity (at private companies, you may have no way to sell the shares after exercising, leaving you holding illiquid stock), and opportunity cost (exercising requires paying the strike price in cash, which has alternative uses). Early exercise — exercising options before they vest, often available for ISOs at private companies — combined with an 83(b) election can start the capital gains clock early and minimize taxes if the company appreciates significantly. This is a strategy most commonly used by early employees and founders at high-growth startups, and it carries real risk if the company fails to appreciate.

Key Decisions When Exercising Options

  • Exercise timing: at a private company, you may exercise during the vesting period or at a liquidity event (acquisition, IPO). At a public company, options can often be exercised and shares sold immediately (a 'cashless exercise').
  • Cash vs. cashless exercise: a cash exercise requires paying the strike price in cash; a cashless exercise (common at public companies) lets you exercise and simultaneously sell enough shares to cover the cost. No cash outlay needed.
  • ISO vs. NSO: know which type you have. ISOs have favorable long-term tax treatment but AMT exposure at exercise; NSOs generate ordinary income at exercise with simpler (if higher) tax treatment.
  • 90-day post-termination window: if you leave the company, you typically have 90 days to exercise vested options or lose them. This is a critical and often overlooked deadline — especially for early employees leaving pre-IPO companies.
  • Early exercise (83(b) election): at private companies, some plans allow early exercise of unvested options. Filing an 83(b) election within 30 days of early exercise can significantly reduce future taxes. Miss the 30-day window and this strategy is no longer available.
  • AMT planning for ISOs: exercise ISOs in a year when your other income is low to minimize AMT exposure. Consult a tax advisor before large ISO exercises — the AMT calculation is complex.

The 90-Day Departure Trap

The 90-day post-termination exercise window is one of the most financially painful surprises in the startup world. Employees who leave a company with significant unvested options often also hold large numbers of vested but unexercised ISOs — and if they don't have the cash to exercise within 90 days of departure, those options lapse permanently. This problem is acute at pre-IPO companies where options may have high strike prices, significant AMT exposure on exercise, and no liquid market to sell into. A few companies have extended the post-termination exercise window to 5 or 10 years, recognizing this as an employee-friendly differentiator. If you're evaluating a role with significant option equity, ask specifically about the post-termination exercise window — and factor in whether you'd be able to exercise your options if you had to leave before a liquidity event.

Example

An engineer has 10,000 NSOs at a $5 strike price. After 4 years of vesting, all 10,000 are vested. The company is now worth $25/share. She exercises all 10,000 shares: cost = $50,000 (10,000 × $5). The spread = $200,000 (10,000 × $20). For NSOs, the $200,000 spread is ordinary income in the year of exercise — taxed at her marginal rate plus applicable state taxes. If she's in the 32% federal bracket plus 9.3% California state, she owes approximately $83,000 in taxes on the exercise. She plans for this by exercising in December to give herself the next January to set aside tax payments. Her cost basis in the shares is $25/share; any appreciation above that will be taxed as capital gains.