RSUs and ISOs: A Tax Guide to Equity Compensation

Equity compensation is one of the most valuable benefits offered by employers — particularly in the technology, finance, and startup sectors. But Restricted Stock Units (RSUs) and Incentive Stock Options (ISOs) are also among the most misunderstood components of a compensation package when it comes to taxes. Getting the tax treatment wrong can mean unexpected bills, missed planning opportunities, or costly AMT exposure.

Here is a clear breakdown of how each type of equity compensation works and what you need to know to manage the tax consequences effectively.

An RSU is a promise by your employer to deliver shares of company stock to you at a future date — typically when a vesting condition is met (time-based, performance-based, or both). Unlike stock options, RSUs have no exercise price. You simply receive shares when they vest.

RSUs are taxed as ordinary income at the time of vesting — not when they are granted. The taxable amount is the fair market value (FMV) of the shares on the vesting date, regardless of whether you sell the shares immediately or hold them.

Your employer will typically withhold federal and state income tax, Social Security, and Medicare at vesting — often by withholding a portion of the shares themselves (called "sell-to-cover" or "net settlement"). The value of the shares withheld is remitted to the IRS on your behalf.

Example: You receive 500 RSUs that vest when the stock is trading at $40 per share. You recognize $20,000 of ordinary income at vesting. If your employer withholds 22% ($4,400), you receive 390 shares and 110 shares are withheld for taxes.

Once RSUs vest and you hold the shares, any subsequent gain or loss is treated as a capital gain or loss — measured from the FMV on the vesting date (your new cost basis).

• If you sell within one year of vesting: short-term capital gain (taxed as ordinary income)
• If you sell more than one year after vesting: long-term capital gain (taxed at 0%, 15%, or 20% depending on your income)

For most employees, selling immediately at vesting eliminates capital gains exposure entirely — you have already paid ordinary income tax on the full value, and there is no additional gain if the price has not moved.

Under-withholding: Employer withholding on RSUs is often at the flat supplemental rate (22% federal), which may be significantly lower than your actual marginal rate if you are in the 32%, 35%, or 37% bracket. This creates a tax shortfall that must be covered through estimated tax payments or at filing.

Forgetting the cost basis: When you sell RSU shares, your broker may report the full proceeds on Form 1099-B without accounting for the income already recognized at vesting. If you do not report your correct cost basis, you will pay tax twice on the same income.

Missing the W-2 income: RSU income is included in Box 1 of your W-2. Make sure your tax preparer knows you have RSUs so the income is not double-counted.

An ISO is the right to purchase company stock at a fixed price (the exercise price or strike price), typically set at the FMV on the grant date. ISOs are a form of stock option available only to employees (not contractors or directors) and must meet specific IRS requirements.

The key advantage of ISOs over non-qualified stock options (NSOs) is their preferential tax treatment — if you meet the holding period requirements, the spread at exercise is not subject to ordinary income tax or payroll taxes.

ISOs have a two-stage tax event:

Stage 1 — Exercise: When you exercise an ISO (purchase the shares at the strike price), you do not recognize ordinary income. However, the spread — the difference between the FMV at exercise and the exercise price — is an Alternative Minimum Tax (AMT) preference item. This can trigger AMT liability even though you have not sold the shares and received no cash.

Stage 2 — Sale: When you sell the shares, the tax treatment depends on whether you meet the qualifying disposition holding period:

• Qualifying disposition: You hold the shares for at least two years from the grant date AND at least one year from the exercise date. The entire gain (from exercise price to sale price) is taxed as long-term capital gain — no ordinary income, no payroll taxes.
• Disqualifying disposition: You sell before meeting both holding periods. The spread at exercise is taxed as ordinary income in the year of sale, and any additional gain is capital gain.

The AMT is the most significant risk associated with ISOs. When you exercise ISOs and hold the shares, the spread is added to your AMT income — even though you have not sold the stock and have no cash to pay the tax.

Example: You exercise ISOs to purchase 10,000 shares at $5 (your strike price) when the FMV is $25. The spread is $200,000. That $200,000 is an AMT preference item. If you are subject to AMT, you could owe tens of thousands of dollars in tax — on stock you have not yet sold.

If the stock subsequently declines in value before you sell, you can end up in a situation where you owe more in AMT than the shares are currently worth. This is the "AMT trap" that caught many employees during the dot-com crash.

The good news: AMT paid on ISO exercises generates an AMT credit that can be used to offset regular tax in future years when your regular tax exceeds your AMT. The credit is not lost — but it may take years to fully recover, and it provides no relief in the year the AMT is owed.

Exercise early in the year: If you plan to exercise and hold, doing so early in the year gives you more time to monitor the stock price and potentially sell before year-end if the stock declines — limiting AMT exposure.

Model your AMT before exercising: Before exercising a large block of ISOs, run a projection to determine how much AMT you will owe. This allows you to exercise only as many shares as you can afford to hold without creating an unmanageable tax bill.

Spread exercises over multiple years: Rather than exercising all ISOs at once, spreading exercises across multiple tax years can keep AMT exposure manageable each year.

Consider a same-day sale (disqualifying disposition): If AMT exposure is too high, selling the shares immediately upon exercise (a "cashless exercise") triggers ordinary income treatment — but eliminates the AMT risk entirely. You give up the preferential capital gains rate but avoid the cash flow problem.

Equity compensation requires proactive planning — not just reactive filing. Key year-end considerations include:

• Estimating RSU income from upcoming vesting events and adjusting withholding or estimated payments accordingly
• Modeling ISO exercise scenarios to optimize between AMT exposure and long-term capital gains treatment
• Tracking holding periods to ensure qualifying disposition treatment on ISO shares
• Harvesting capital losses to offset gains from RSU or ISO share sales
• Reviewing cost basis records to ensure accurate reporting on Form 8949

RSUs and ISOs are not standard W-2 income — they require specialized knowledge of AMT rules, holding period tracking, cost basis reporting, and multi-year planning. A general tax preparer who is unfamiliar with equity compensation can easily miss planning opportunities or create costly errors.

At Autarky Tax and Accounting, our CPAs and Enrolled Agents work with employees, executives, and founders who receive equity compensation as part of their total package. We help you understand your tax exposure, plan your exercises and sales strategically, and file accurately — so your equity works for you, not against you. Our individual tax services cover the full range of complex compensation situations.

Contact us to schedule a consultation before your next vesting event or ISO exercise.