What ISOs and NSOs Mean for Your Taxes (And Why the Difference Is Expensive)
Sam's List Editorial | 2026-06-23
What ISOs and NSOs Mean for Your Taxes (And Why the Difference Is Expensive) Two engineers at the same startup get the same number of options at the same strike price. One owes nothing the year they exercise. The other gets a five-figure tax bill for stock they haven't sold and can't sell. The only difference: one set of options was labeled ISO and the other NSO. That's the entire game with ISO vs NSO tax . The letters on your grant document quietly decide when you get taxed, how you get taxed, and whether the IRS asks you to pay tax on paper gains you can't spend. Most employees never read past "stock options — congrats." Here's what actually happens. ISOs Can Get Capital Gains Treatment — If You Survive the Holding Period Incentive stock options (ISOs) are the friendlier-looking of the two, and the trap is hidden inside that. When you exercise an ISO, there's no regular income tax at exercise. None. If you then hold the shares long enough — more than two years from the grant date and more than one year from the exercise date — the entire gain from your strike price to your sale price is taxed as long-term capital gain. That's the lower rate, often 15% or 20% federally instead of ordinary rates that climb to 37%. That's the dream scenario. Buy at a $2 strike, sell years later at $40, and the $38 spread is a long-term gain instead of a paycheck. The catch is the word "survive." If you sell early — a "disqualifying disposition" — the favorable treatment evaporates and part of the gain snaps back to ordinary income. The tax code rewards patience and punishes the people who panic-sell. The AMT Surprise That Catches People Who Exercise and Hold Here's the thing nobody tells you about ISOs: exercising and holding can trigger the alternative minimum tax. For regular tax, exercising an ISO is a non-event. But for the alternative minimum tax (AMT), the spread between fair market value and your strike price — the "bargain element" — counts as income the year you exercise, under IRC §56(b)(3). You bought stock and sold nothing, and the AMT system still says you have income. Consider a typical example. You exercise 10,000 ISOs at a $2 strike when the 409A fair market value is $12. That's a $10 spread, or $100,000 of bargain element. For regular tax, zero. For AMT, that $100,000 gets added to your alternative minimum taxable income, and depending on your other income it can produce a real tax bill — easily $15,000 to $25,000 — on shares you can't sell because the company is still private. This is the AMT ISO exercise problem in one sentence: you can owe cash tax on...
