ISO Vs RSU: Which Is Better
ISOs and RSUs are taxed in fundamentally different ways — understanding which one actually benefits you depends on your income, timeline, and AMT exposure.
Neither is better. The one that costs you less tax is better, and that answer changes depending on 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, here is what actually separates them.
How Each One Works
An 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 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 20 percentage points or more.
The catch: ISO exercises create an 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% withholding your company applies does not cover those in the 32%, 35%, or 37% brackets. That gap surfaces quietly at filing.
ISOs require more planning. You could exercise at a $50 spread, hold through a correction, sell at a $10 gain, and still owe AMT on that original $50 spread from the exercise year.
One 2026 limit worth knowing: ISOs are capped at $100,000 per year in vesting value based on grant-date fair market value. Anything above that converts to 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 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 meaningfully 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 large check in April without selling a share.
ISOs win when the stock appreciates significantly 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-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?
You accumulate a minimum tax credit that offsets future regular tax liability, but timing and income levels in future years determine when you can actually use it.
What to Do Next
What decides this is 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.
Where it goes wrong: 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, the coordination between exercise timing, AMT exposure, and your other income is too consequential to treat as a side project. That is the kind of conversation worth having 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 — verify current rules before acting. Consult with qualified professionals for guidance specific to your situation.
More in this guide
This is one piece of a bigger picture. For the full strategy, see our pillar guide:
Equity Compensation: A Practical Guide to RSUs, ISOs, and NSOs →Or see how we handle this for clients:
Tax Optimization →The information provided is for educational purposes only and does not constitute investment, legal, or tax advice. All investing involves risk, including the potential loss of principal. Consult with a qualified financial professional before making any financial decisions. Securities and advisory services offered through LPL Financial, a Registered Investment Advisor. Member FINRA & SIPC.
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