What 'stock options' actually are
A stock option is the right — not the obligation — to buy a share at a pre-set strike price. If the company's share price rises above the strike, the option is "in the money" and can be exercised for a profit. If the price stays below the strike, the option is "underwater" and expires worthless.
Example. You're granted 10,000 options at a $3 strike price. Four years later, the company is public and trading at $18. Exercising: buy 10,000 × $3 = $30,000 worth of shares. Immediately sellable for 10,000 × $18 = $180,000. Pre-tax gain: $150,000.
The same 10,000 options if the company stays at $3 or goes out of business: worth zero. Options are leveraged bets on upside — they magnify gains but require the company to actually grow to have any value.
ISO vs NSO — the tax treatment difference
Incentive Stock Options (ISOs): Granted to employees only. No regular-income tax at exercise; AMT may apply. If held 1+ year post-exercise and 2+ years post-grant, the gain at sale is taxed as long-term capital gains (0-20% federal). The favorable tax treatment is why ISOs are candidate-friendly — but AMT can surprise you.
Non-qualified Stock Options (NSOs): Can be granted to employees, contractors, advisors, or directors. Difference between strike and fair market value at exercise is taxed as ordinary income. Further gain after exercise is taxed as short- or long-term capital gain depending on holding period.
Most startups grant ISOs to employees and NSOs to non-employees. When you receive an equity grant, read the agreement and confirm the type.
The AMT trap on ISO exercises
When you exercise ISOs while still holding the stock, the "bargain element" (FMV - strike price × shares) is added to your Alternative Minimum Taxable income. This can trigger a material AMT bill even though you haven't sold the stock.
Example. 10,000 ISOs at $2 strike, current 409A valuation $12. Bargain element: ($12 - $2) × 10,000 = $100,000 added to AMT income. For a single-filer in a high-income year, that can trigger an AMT bill of $15-25k — owed in cash, in the year of exercise, even though the stock is still illiquid in a private company.
Rule of thumb: before exercising ISOs, model the AMT impact. Many tax professionals recommend exercising small amounts across multiple years to avoid AMT cliffs. Use Secfi or CarryMoney-style platforms (or a CPA) to run the projection.
Private company options — discount aggressively
At a private company, your strike price is set by the latest 409A valuation. The 409A is usually 20-40% below the last preferred-round price. Your options have "fair value" tax basis at the 409A price, but the real economic outcome depends on a future liquidity event (IPO, acquisition, secondary).
The honest discount: multiply the theoretical value of your options by a probability of exit. 40% of seed-stage startups return zero; 70-80% of Series A startups return less than invested capital. A 0.1% stake in a pre-revenue startup at a $50M valuation has a "theoretical" value of $50k but an expected value (probability-weighted) of $10-20k.
Don't model your options at the last round price. Model at three scenarios: (1) dead (0x), (2) modest acquisition (1-2x the last valuation), (3) big exit (5-10x). Decide based on the middle scenario, not the best-case.
The post-termination exercise window
Most options come with a 90-day post-termination exercise window: if you leave the company, you have 90 days to exercise your vested options or lose them. This is candidate-unfriendly at private companies because you'd owe strike price + potential AMT in cash for illiquid shares.
Candidate-friendly alternatives: extended post-termination exercise (7-10 years), commonly offered by Coinbase, Quora, Pinterest, and others. If you're interviewing at a private company with a 90-day window, ask: "Can we extend the post-termination exercise period to 10 years?" Many companies will accommodate for senior hires.
The math: a 90-day window forces a cash-or-forfeit decision within 3 months of leaving. An extended window lets you wait until there's a liquidity event to decide. This is worth negotiating hard.
Exercise-and-sell strategy at IPO
At IPO, vested options become exercisable and (after any lockup period, typically 180 days) shares become sellable. The common strategy: exercise and immediately sell some shares to cover the tax, hold the rest for long-term capital gains treatment.
Example. 20,000 ISOs at $2 strike, stock at $50 post-IPO. Bargain element at exercise: $960,000. Sell 40-50% of the shares to cover AMT + exercise cost = $48k exercise + $180-220k AMT reserve. Hold the remaining shares until 1 year post-exercise to qualify for long-term capital gains.
Strategy details depend on your cost basis, AMT situation, and concentration risk. For grants above $100k in value, work with a CPA who specializes in equity compensation before exercising.
Disclaimer
This is not tax, legal, or financial advice. Stock option taxation is complex and varies by ISO vs NSO classification, holding periods, AMT interaction, state tax, and your overall income profile. For any option exercise worth more than a few thousand dollars, consult a CPA or CFP who specializes in equity compensation before acting. Private company equity is highly uncertain; model conservatively and never stake more than you can afford to lose.