ISO Vs RSU: Which Is Better

The better one is the one that costs you less tax, and that answer changes with your income, your company's stock trajectory, and how long you're willing to wait. If you just received an offer letter with a mix of both, start with how each one is taxed.

How Each One Works

A restricted stock unit (RSU) is a promise. Your company grants you shares, they vest on a schedule, and on the day they vest you owe ordinary income tax on the value. The IRS treats them like a paycheck.

An incentive stock option (ISO) is a right to buy shares at a fixed price, called the strike price. You are not taxed when you receive it, and not taxed when you exercise it under the regular income tax system. If you hold the shares long enough after exercising (one year from exercise, two years from grant), any gain at sale is taxed at long-term capital gains rates. For a high earner, that difference can be about 15 to 17 percentage points federally (37% ordinary income plus Medicare tax on RSU wages, against 20% plus the 3.8% net investment income tax on long-term gains).

The catch: ISO exercises create an alternative minimum tax (AMT) preference item. The spread between your strike price and the fair market value at exercise is added back for AMT purposes, and the bill can arrive before you've sold a single share.

The Rules, Tradeoffs, and Watchouts

RSUs are simpler. The bill is predictable, but the default 22% federal withholding on supplemental wages (37% only on supplemental wages above $1M in a year) does not cover those in the 24%, 32%, 35%, or 37% brackets. That gap shows up at filing.

ISOs require more planning. You could exercise at a $50 spread, hold through a correction, sell in a later year at a $10 gain, and still owe AMT on that original $50 spread from the exercise year (some of it may come back over time as an AMT credit).

One limit worth knowing (it is not indexed for inflation): ISOs are capped at $100,000 per year in vesting value based on grant-date fair market value. Anything above that converts to nonqualified stock option (NSO) treatment automatically. Many tech employees hit this ceiling without realizing it. The AMT exemption also phases out at higher income levels, so your effective AMT exposure on a large ISO exercise can be higher than a planning calculator suggests.

When One Clearly Wins

Two high earners not rich yet (HENRYs) at the same company, same grant date, same $500,000 equity award (illustrative).

The first receives RSUs. At vesting, she pays ordinary income tax at 37% federal and keeps roughly $315,000 after tax. No AMT exposure, no holding period risk.

The second receives ISOs with a $1 strike price on stock now worth $50. He exercises, holds three years, sells at $80, and pays 20% long-term capital gains plus 3.8% net investment income tax. He keeps more than the RSU holder. But in the exercise year he had an AMT item equal to the full spread, and without planning, he wrote a check to the IRS in April without selling a share.

ISOs win when the stock appreciates and you can absorb the AMT exposure in the exercise year. RSUs win when simplicity and liquidity matter more, or when your marginal rate advantage over capital gains is smaller than it looks on paper.

How This Connects to Your Equity Compensation Plan

This decision sits inside a larger set of choices around equity compensation. The full picture, including how the AMT trap works in detail, what happens when you layer ISOs and NSOs together, and how to manage concentration risk once shares vest, is covered in Equity Compensation: A Practical Guide to RSUs, ISOs, and NSOs.

Frequently Asked Questions

Can I have both ISOs and RSUs from the same employer?

Yes, and many tech and pre-initial public offering (pre-IPO) packages include both. The tax treatment runs completely separately for each grant.

Do RSUs ever qualify for long-term capital gains treatment?

Only on appreciation after vesting. The value at vest is always ordinary income; gains above that basis receive capital gains treatment if you hold the shares.

What triggers the $100,000 ISO limit?

The limit applies to the grant-date fair market value of shares that become exercisable in a single calendar year, with the excess converting to NSO treatment automatically.

Is the AMT credit refundable if I pay AMT on an ISO exercise?

No. You accumulate a nonrefundable minimum tax credit that offsets future regular tax liability, and timing and income levels in future years determine when you can use it.

What to Do Next

This decision turns on your effective marginal rate in the vesting or exercise year, your AMT position, and whether you have the balance sheet to hold ISO shares through the required periods without forcing a sale.

A common misstep: people exercise ISOs in a strong year, plan to hold, then face a correction and sell before the holding period is met. That triggers a disqualifying disposition and loses the capital gains treatment. The AMT preference item from the exercise year still stands.

If your equity package is worth more than one year's salary, or you are inside 18 months of a liquidity event, exercise timing, AMT exposure, and your other income are worth coordinating with an advisor who works through this regularly.

The information provided is for educational purposes only and does not constitute investment, legal, or tax advice. Tax law changes frequently, so verify current rules before acting. Consult with qualified professionals for guidance specific to your situation.