Stock Options Tax Impact Calculator
Model the federal tax cost of exercising ISO (Incentive Stock Options) vs NSO (Non-Qualified Stock Options) at various sale timings.
ISO vs NSO — The Critical Distinction
ISOs (Incentive Stock Options): Tax-advantaged stock options under IRS Section 422. No ordinary income at exercise. If you hold 1+ year from exercise AND 2+ years from grant (qualifying disposition), the entire gain at sale is long-term capital gains (15-20%). Catch: the bargain element at exercise (FMV minus strike, times shares) becomes an AMT preference item that year — can trigger Alternative Minimum Tax owing potentially tens of thousands of dollars in the exercise year.
NSOs (Non-Qualified Stock Options): No special tax treatment. At exercise, the bargain element (FMV minus strike) is ordinary income — taxed at your marginal rate AND subject to FICA. No AMT issue. Any gain after exercise is capital gain. Sources: IRS Section 422, Section 83, Form 6251 instructions. Last updated: May 2026.
The ISO AMT Trap
If you exercise ISOs and hold (intending to qualify for long-term capital gains treatment), the bargain element becomes an AMT preference item. Example: exercise 10,000 ISOs at $2 strike when FMV is $20, bargain element = $180,000. This $180K is added to your regular income for AMT calculation — potentially generating $30K-$50K of AMT owed in April even though you haven't sold and have NO CASH.
Pre-IPO employees have lost houses to ISO AMT when the stock subsequently crashed. Always (1) calculate AMT BEFORE exercising, (2) exercise small tranches to spread AMT across years, or (3) plan an early disposition to convert to NSO treatment if AMT would be unsustainable.
Exercise Strategies
(1) Same-day exercise-and-sell. Buy and sell instantly. ISO qualifying disposition disallowed — taxed as ordinary income. NSO: ordinary income at exercise = full gain (no cap gains layer). Simple, no equity risk, no AMT.
(2) Early exercise. Exercise immediately at grant when FMV ≈ strike (bargain element near $0). Start the long-term capital gains clock early. Requires 83(b) election filed within 30 days. Risky — you may lose the exercise cash if the company fails.
(3) Hold qualifying period. Exercise and hold 1+ year (ISO: + 2+ years from grant). Whole gain at sale is long-term capital gains (15-20% federal). Best if you believe in the stock long-term and can manage AMT.
Should You Exercise Before IPO or After?
Pre-IPO exercise: small bargain element (small AMT exposure), starts long-term clock early, but illiquid until IPO. Post-IPO exercise: larger bargain element (huge AMT exposure if ISO), but liquid — you can sell some to cover taxes. Most knowledgeable employees exercise early-stage ISOs when bargain element is small (under $100K-$200K) and hold; they wait on later-stage ISOs and do same-day sells at IPO.
Frequently Asked Questions
What is the difference between ISO and NSO?
ISOs (Section 422) require employee status and are tax-advantaged \u2014 no ordinary income at exercise if you meet holding requirements (1 year post-exercise, 2 years post-grant). NSOs have no special treatment \u2014 bargain element is ordinary income at exercise. ISOs have an AMT trap; NSOs do not. Most early employees get ISOs; later employees and contractors get NSOs.
What is the 83(b) election?
An IRS election that lets you pay tax at grant on the bargain element of restricted stock or early-exercised options \u2014 converting future appreciation to capital gains. Must be filed within 30 days of acquisition. Costs current ordinary income tax but locks in long-term cap gains treatment for future gain. Common with early-stage startups.
Can I get AMT credit back in future years?
Yes. AMT paid creates an AMT credit that can be applied to regular tax in future years when your regular tax exceeds AMT. The credit is non-refundable but has no expiration \u2014 you can carry it forward indefinitely. Many ISO exercisers recover much of their AMT in 2-5 years.
What is a qualifying disposition?
ISO sale that meets BOTH (1) 1+ year after exercise, AND (2) 2+ years after grant. Triggers preferential tax treatment \u2014 entire gain at sale is long-term capital gains. Disqualifying disposition (selling earlier) forfeits ISO benefits \u2014 bargain element becomes ordinary income, future gain is short or long-term cap gains.
Are stock options taxed when granted?
Generally no. Both ISOs and NSOs have no tax at grant. ISOs are taxed at exercise (AMT) and sale. NSOs are taxed at exercise (ordinary income) and sale (capital gains). Restricted Stock (not options) IS taxed at grant unless you make 83(b) election \u2014 that's a key distinction from options.
Should I exercise my options before leaving the company?
Most option plans give 90 days post-employment to exercise vested options \u2014 after which you lose them. Before leaving: (1) calculate exercise cost and AMT, (2) consider whether you have liquidity to exercise without selling other assets, (3) compare to current FMV. Many employees exercise within the 90-day window even at cost \u2014 losing options entirely is usually worse than the AMT risk.