Equity compensation comes in three primary forms — Incentive Stock Options (ISOs), Non-Qualified Stock Options (NSOs), and Restricted Stock Units (RSUs) — and each follows completely different tax rules at every stage from grant to sale. Misunderstanding these rules costs employees thousands of dollars annually through premature exercises, missed holding periods, and unexpected Alternative Minimum Tax bills. The fundamental distinction is timing: when does a taxable event occur, and is the income taxed as ordinary income or capital gains? For NSOs and RSUs, the answer is relatively straightforward — ordinary income at exercise or vesting, respectively. For ISOs, the rules create both opportunity and risk through a deferred tax treatment that can backfire spectacularly via the AMT. Whether your equity package is worth $50,000 or $5 million, understanding the tax mechanics is the difference between optimizing your compensation and leaving money on the table.
Restricted Stock Units are the most common form of equity compensation at public companies, and their tax treatment is the most straightforward. RSUs are a promise to deliver shares of stock on a future vesting date — you own nothing until they vest. When RSUs vest, the fair market value of the shares on that date is taxed as ordinary income, subject to federal income tax, state income tax, Social Security (up to the wage base of $176,100 in 2026), and Medicare tax (including the 0.9% Additional Medicare Tax on earnings above $200,000). Your employer withholds taxes at vesting, typically by selling a portion of the shares — a process called "sell to cover." If 100 RSUs vest when the stock price is $150, you have $15,000 in ordinary income. At a combined withholding rate of roughly 40% (22% federal supplemental rate + FICA + state), approximately 40 shares are sold for taxes and you receive 60 shares. Your cost basis in those 60 shares is $150 per share. If you sell at $180 later, you pay capital gains tax on the $30 per share appreciation — long-term if held over one year from the vesting date, short-term if not.
Non-Qualified Stock Options give you the right to buy company stock at a predetermined strike price. No tax event occurs at grant. The taxable event happens when you exercise — buy the shares. The spread between the fair market value at exercise and your strike price is taxed as ordinary income, subject to all payroll taxes. If your strike price is $20, the stock is at $85 when you exercise, and you exercise 1,000 options, the spread is $65 per share × 1,000 = $65,000 in ordinary income. Federal tax at the 24% bracket: $15,600. FICA on $65,000: $4,973. State tax in California at roughly 9.3%: $6,045. Total tax at exercise: approximately $26,618, or 41% of the spread. After exercise, your cost basis is $85 per share (the FMV at exercise). Any subsequent gain or loss from $85 is a capital gain or loss. The key planning consideration with NSOs is timing: if you believe the stock will appreciate significantly, exercising earlier means less ordinary income and more potential long-term capital gains treatment on future appreciation.
Incentive Stock Options receive preferential tax treatment — but with a major catch. Like NSOs, ISOs give you the right to buy at a strike price, and no tax is owed at grant. Unlike NSOs, exercising ISOs triggers no regular income tax. The spread at exercise is not subject to ordinary income tax or payroll taxes. Instead, if you hold the shares for at least two years from the grant date and one year from the exercise date, the entire gain from strike price to eventual sale price is taxed as long-term capital gains (0%, 15%, or 20% depending on income). On 1,000 shares with a $20 strike exercised at $85 and sold at $120, qualifying disposition treatment means you pay long-term capital gains on the full $100 per share gain ($100,000 total). At the 15% LTCG rate, that's $15,000 in tax versus approximately $26,600 + additional capital gains tax under NSO treatment. The savings can be enormous.
The AMT trap is the ISO catch that blindsides thousands of employees every year. While the ISO exercise spread isn't subject to regular income tax, it is a preference item for the Alternative Minimum Tax. The AMT is a parallel tax system that adds back certain deductions and income items, applies a flat 26% or 28% rate, and requires you to pay the greater of your regular tax or AMT. If you exercise ISOs with a large spread — say $200,000 — that amount gets added to your AMT income. The 2026 AMT exemption is approximately $88,100 for single filers, so $200,000 in ISO spread minus the exemption leaves roughly $111,900 subject to 26% AMT, creating a potential AMT bill of $29,094 — on income you haven't actually realized as cash. This is how employees of pre-IPO companies end up with six-figure tax bills on paper gains that later evaporate if the stock price drops. The AMT paid does create a credit you can use in future years, but the cash flow impact is immediate. Before exercising a large ISO position, model the AMT impact using tax software or a CPA.
State tax implications add another layer of complexity. California taxes all equity compensation as ordinary income at the time of exercise or vesting, with rates up to 13.3%. If you were a California resident when ISOs were granted and later moved to Texas, California may still claim a portion of the income based on the ratio of time the options were earned in California. New York applies a similar allocation method. Washington State imposes a 7% capital gains tax on gains exceeding $270,000, which can affect the sale of vested equity. For planning purposes, the highest-impact strategies are: (1) exercise ISOs in January to create the longest possible window to meet the qualifying holding period before year-end tax planning; (2) exercise only enough ISOs per year to stay below the AMT threshold; (3) for NSOs, consider exercising in a year when your other income is lower; (4) for RSUs, recognize that you have no control over vesting-date taxation but full control over when to sell the after-tax shares and whether to hold for long-term capital gains treatment on post-vest appreciation. A tax-aware equity strategy, implemented consistently over a multi-year vesting schedule, can save 5-15% of your total equity compensation value.