ISOs, NSOs, and RSUs: How Each Type of Equity Compensation Is Taxed

As a startup expands, new hires are more likely to receive options or units instead of restricted stock as part of their compensation. The company starts to hand out different equity grands, most commonly NSOs (Non-Qualified Stock Options), ISOs (Incentive Stock Options), and RSUs (Restricted Stock Units). Each grant type gets taxed on a different timeline. Learning how your specific equity works gives you a chance to plan your finances and avoid a sudden large tax bill.

NSOs (Non-Qualified Stock Options): How and When You’re Taxed

Among the three, NSOs are the simplest and most straightforward. NSOs give you the right to buy shares of company stock at a set discount price (also known as strike price). You do not owe taxes when the company grants these options or when you vest them over time. You get taxes on the day you buy the shares. When you exercise an NSO, the IRS taxes the gap between what you pay for the share and what it’s actually worth, which is called the spread. This spread is treated as regular income, so your employer is required to automatically withhold taxes on that difference.

ISOs (Incentive Stock Options): Tax Benefits and the AMT Risk

ISOs work a bit differently. They are tax-advantaged options available exclusively for employees, provided the grant follows specific IRS guidelines under Section 422. The main benefit of an ISO is that buying the stock doesn’t trigger standard income tax or nor does your employer withhold taxes from your paycheck on that day.

However, ISOs come with a hidden downside: they can trigger the Alternative Minimum Tax or AMT. The AMT is a parallel tax system that treats your paper profits (the difference between the stock’s current fair market value and your lower purchase price) as actual taxable income for that year. This means you are required to pay whichever calculation produces the higher tax bill: your standard income tax or your AMT calculation, meaning you could end up owing a significant cash tax payment in the year you exercise, even if you haven’t sold any shares to generate actual cash profit, and even if the stock price crashes after.

The real advantage of an ISO is in the tax savings when you finally sell your stock. If you meet two specific timing rules: 1) you hold the stock for at least two years from the day the options were granted; and 2) hold the stock at least one year from the day you exercised (bought) the stock before selling them. Once you meet these criteria, your entire profit qualifies to be taxed as long-term capital gains. However, if you sell your shares before meeting both these holding requirements, you lose the tax advantage and a portion of your gains gets bumped back up to be taxed in higher, ordinary income rates. Note that the IRS puts a cap on how many ISOs can vest in a single calendar year – that is, only up to $100,000 worth of stock can vest as ISOs per year. If you have options that vest above this limit, the excess are automatically treated as standard NSOs instead.

RSUs (Restricted Stock Units): When Taxes Hit Automatically

RSUs operate on a completely different set of rules from options. An RSU isn’t an option to buy any shares. It is simply a promise from your employer to give your actual shares of stock once you meet certain milestone, like staying at the company for a set period.

Because you don’t receive any stock when an RSU is granted, you cannot file a section 83(b) election since this only applies when you actually own the stock upfront.

The tax for an RSU gets triggered when your shares vest and your company delivers them to your account also known as settlement. During this time, the fair market value of the stock is taxed as regular income similar to when a bonus gets taxed. When you sell the stock later on, you only pay capital gains tax (or claim a capital loss) on the price difference between that original starting value and your final sale price.

NSOs vs. ISOs vs. RSUs: Who Controls the Tax Timing

When you look at equity compensation, the difference between these awards comes down to two factors: when the IRS taxes your earnings as regular income and who controls that timing. With NSOs, you choose when your income tax gets triggered by deciding when to exercise your options, and you are taxed on the spread between your purchase prices and the stock’s current market value. With ISOs, you can avoid regular income tax and have your profit taxed at lower long-term capital gains rates, as long as you hold the shares long enough to meet the time requirements. With RSUs, you have no control over the timing; income tax hits you automatically as soon as your shares vest and land in your account.

Know Your Grant Type Before You Plan

Because each grant follows completely different tax rules, your first move should always be checking your grant paperwork to confirm your exact award type. Confirming which type of equity you hold is the single most important step in preparing your finances and avoiding a costly tax bill.

This overview focuses on the common federal-income tax treatment of employee equity awards. State, local, and international taxes, deferred-compensation rules, company-specific plan terms, and special elections such as Section 83(i) for certain private-company awards can all produce different results.

This article is for general educational purposes only and does not constitute tax, legal, or accounting advice, nor does it create an advisory-client relationship. Tax law changes, and the right answer depends on your specific facts. Consult a qualified tax advisor before making decisions based on anything here.