PersonalCFO

Stock Option Tax Calculator

Calculate the tax impact of exercising stock options. ISOs and NSOs have fundamentally different tax treatment — ISOs trigger AMT instead of regular income tax, while NSOs generate ordinary income and FICA taxes on the spread at exercise.

Option Details

$
Price you pay per share
$
Fair market value per share

Your Income

$

Exercise Summary

Spread per Share
$25.00
$35.00 - $10.00
Total Spread (Gain)
$25,000
1,000 shares
Exercise Cost
$10,000
Cash needed to exercise
Shares Value at FMV
$35,000
Total value after exercise

Tax on Exercise (NSO)

Federal Income Tax
$6,000
On spread as ordinary income
Total Tax on Exercise
$6,000
24.0% of spread
NSO spread of $25,000 is taxed as ordinary income (W-2 supplemental income). This includes federal income tax, Social Security (up to wage base), and Medicare.
Total Gain
$25,000
Tax Cost
$6,000
Net After Tax
$19,000

ISO vs NSO Comparison

ISONSODifference
Ordinary income on exercise$0$25,000ISO saves $25,000
FICA taxes$0$0No FICA on ISOs
AMT impact$0$0None
State tax on exercise$0$0$0
Total tax on exercise$0$6,000ISO saves $6,000
Net after tax$25,000$19,000

ISO comparison assumes qualifying disposition (held >1 year from exercise, >2 years from grant). A disqualifying disposition is taxed like an NSO.

ISO vs NSO: How Stock Option Taxes Work

Incentive Stock Options (ISOs) receive favorable tax treatment: no regular income tax or FICA at exercise. However, the spread (FMV minus strike price) is an AMT preference item. If the spread is large enough, you may owe Alternative Minimum Tax. When you eventually sell, gains are taxed as long-term capital gains if you meet both holding periods (1 year from exercise, 2 years from grant).

Non-Qualified Stock Options (NSOs) are simpler but more expensive at exercise. The spread is ordinary income — subject to federal income tax, state tax, Social Security (up to the wage base), and Medicare taxes. The upside: your cost basis is set to FMV at exercise, so future gains are only on appreciation above FMV.

The AMT trap with ISOs. Exercising ISOs in a year when your stock has appreciated significantly can trigger a large AMT bill — even though you received no cash. Many employees discover this only at tax time. This calculator shows the AMT impact before you exercise.

Qualifying vs. disqualifying dispositions. If you sell ISO shares before meeting the holding period requirements (1 year from exercise + 2 years from grant), it becomes a disqualifying disposition. The spread at exercise is taxed as ordinary income — essentially the same as an NSO. Plan your sales carefully.

Strategy: exercise ISOs early. If you believe in the company, exercising ISOs early (when the spread is small) minimizes AMT exposure. The earlier you exercise, the sooner the holding period clock starts, and the smaller the AMT preference item.