Stock Options: ISOs, NSOs, and the AMT Trap
June 2026 · 11 min read
Stock options are the original form of tech equity compensation, and they're still the standard at startups. The basic idea: your company gives you the right to buy stock at a fixed price (the "strike price"). If the stock goes up, you buy at the lower price and profit from the difference.
Simple enough. But there are two flavors — ISO and NSO — and picking the wrong move with ISOs can put you in serious tax trouble. Let's go through it.
ISO and NSO: the quick version
| ISO | NSO | |
|---|---|---|
| Who gets them | Employees only | Anyone — employees, contractors, advisors |
| Tax at exercise | No regular income tax. But may trigger AMT. | Taxed as ordinary income immediately |
| Tax at sale | Long-term capital gains if you hold long enough | Capital gains on appreciation after exercise |
| The catch | AMT can surprise you with a huge bill | You pay ordinary income on the spread — up to 37% |
| $100K limit | Only $100K can first vest per year | No limit |
NSOs: simple but expensive
Non-Qualified Stock Options are the straightforward ones. When you exercise, the difference between the market value and your strike price is treated like a cash bonus — it goes on your W-2 as ordinary income. Your employer withholds taxes. Done.
If you later sell the shares for a profit above the exercise price, that additional gain is a capital gain (short or long term depending on holding period).
NSOs are common for contractors and advisors because the company doesn't have to worry about the employee-only ISO rules. From a tax perspective, they're worse than ISOs — but they're also simpler and harder to screw up.
ISOs: better on paper, dangerous in practice
Incentive Stock Options have a huge tax advantage: if you follow the rules, your entire profit is taxed as long-term capital gains (15-20%) instead of ordinary income (up to 37%). The rules: hold the shares for at least 1 year after exercise and 2 years after the grant date.
So far so good. Here's the problem.
When you exercise ISOs, the spread between your strike price and the fair market value is added back to your income for Alternative Minimum Tax purposes. AMT is a parallel tax system with its own rates (26-28%) and its own exemption amount. If the AMT calculation exceeds your regular tax, you pay the difference.
This can get ugly fast.
The nightmare scenario (this is real):
You work at a startup with a $1 strike price and the 409A valuation is now $50.
You exercise 10,000 ISOs.
AMT preference item: ($50 - $1) × 10,000 = $490,000.
Your regular income: $150K salary. AMT exemption: ~$88K (phases out at higher incomes).
AMT taxable: ~$552K. AMT owed: roughly $140,000.
You now owe the IRS $140,000 for stock you can't sell because the company is still private.
This is not a hypothetical. It happened to people during the dot-com bubble and it happens today. The key number to watch: if your ISO spread × number of shares approaches or exceeds your regular income, you almost certainly have an AMT problem. Run the numbers before exercising. Hire a CPA who knows equity comp. Don't guess.
The 83(b) election: a genuine tax hack
If your company allows early exercise — meaning you can buy your options before they vest — combined with an 83(b) election, you can potentially pay zero tax on future appreciation.
Here's the mechanics: you exercise immediately after receiving the grant, when the strike price equals the current 409A valuation. The spread is $0, so there's no AMT impact. You file an 83(b) election within 30 days, telling the IRS "tax me now on the $0 gain." Your capital gains clock starts immediately. If you hold for 1+ year after exercise and 2+ years after grant, all appreciation is long-term capital gains.
The risk is that you're buying illiquid startup stock with your own money. If the company goes under, you lose 100% of your exercise cost. Only do this if you can afford to lose that money AND you have enough conviction in the company to bet real cash on it.
A framework for "when should I exercise?"
Rather than a one-size-fits-all rule, here's how I think about it based on the stage:
Pre-seed through Series A
Early exercise + 83(b) if allowed and you believe in the company. The strike price is probably pennies. Your risk is low in absolute dollars.
Series B through pre-IPO
Don't exercise yet unless the spread is tiny. The AMT risk is real at this stage. Wait until you have clarity on a liquidity event, or exercise in small batches to stay under the AMT threshold.
Post-IPO
Exercise and sell (cashless exercise) or exercise and hold if you want to start the capital gains clock. Post-IPO, the stock is liquid — you can sell shares to cover the tax, which makes the AMT risk manageable.
You're leaving the company
You typically have 90 days to exercise vested ISOs after your last day. This deadline is unforgiving. If you miss it, your options expire worthless. Calculate the AMT impact, and if it's manageable, exercise what you can afford. If it's not, it might be worth paying a CPA specifically for this decision.