Stock Options vs. RSUs: Tax Implications for Employees and Founders

Equity is how startups attract talent they couldn't otherwise afford — but the tax treatment of that equity is where many employees and founders get burned. Two grants of identical "value" can produce wildly different tax bills depending on whether they're stock options or RSUs, and depending on when you act. Understanding the differences before you sign (or before you exercise) can be worth tens of thousands of dollars.

This guide breaks down the three most common forms of startup equity — ISOs, NSOs, and RSUs — and exactly when and how each is taxed.

> Note: Equity taxation is genuinely complex and fact-specific (AMT, holding periods, 409A valuations all interact). This is an educational overview, not personal advice. Talk to a CPA before exercising options or making decisions with real dollars attached.

First, the big picture: options vs. units

Stock options give you the right to buy shares at a fixed price (the "strike" or "exercise" price), usually set at fair market value when granted. You choose whether and when to exercise. Options come in two flavors: ISOs (incentive stock options) and NSOs (non-qualified stock options).

RSUs (restricted stock units) are a promise to deliver shares (or cash) for free once they vest. There's nothing to buy — and nothing to decide. When they vest/settle, you simply receive shares.

That structural difference — option to buy vs. promise to give — drives everything about how they're taxed.

Incentive Stock Options (ISOs)

ISOs are the most tax-favored equity, and they're reserved for employees.

At grant: no tax.

At vesting: no tax.

At exercise: no regular income tax. But the "bargain element" (the difference between fair market value and your strike price) is an adjustment for the Alternative Minimum Tax (AMT). This is the classic trap — you can owe AMT on a paper gain in a private company whose shares you can't yet sell.

At sale: if you hold the shares long enough to make a "qualifying disposition" — more than 2 years from grant and more than 1 year from exercise — your entire gain is taxed as long-term capital gain. Miss those holding periods (a "disqualifying disposition") and part of the gain becomes ordinary income.

The upside: ISOs can convert your entire gain to favorable long-term capital-gains rates. The risk: AMT at exercise can create a tax bill before you have any cash from the shares. Timing your exercise carefully — and modeling AMT — is everything.

Non-Qualified Stock Options (NSOs)

NSOs are simpler and more flexible (they can go to contractors, advisors, and board members, not just employees), but less tax-favored.

At grant: no tax (assuming the strike is at fair market value).

At vesting: no tax.

At exercise: the bargain element (FMV minus strike price) is taxed as ordinary income right away — and for employees, it's subject to payroll tax withholding. This happens whether or not you sell the shares.

At sale: any further gain after exercise is capital gain (long- or short-term depending on how long you held).

The trade-off: no AMT complexity, but you pay ordinary-income tax at exercise on the spread, with no qualifying-disposition path to convert that piece to capital gains.

Restricted Stock Units (RSUs)

RSUs are the simplest to understand and the most common at later-stage and public companies.

At grant: no tax.

At vesting/settlement: the full fair market value of the shares is taxed as ordinary income — and subject to payroll withholding. You're taxed on the whole value, not a spread, because you paid nothing.

At sale: any gain or loss after vesting is capital gain/loss, measured from the value already taxed at vesting.

The key issue: you owe ordinary-income tax when RSUs vest whether or not you sell — and at a private startup, you may not be able to sell to cover the bill. Many companies handle this by withholding ("selling to cover") some shares at vesting, but at a private company that's not always possible, so plan for the cash impact.

Important — no 83(b) for RSUs. Founders sometimes ask about filing an 83(b) election on RSUs. You can't — the 83(b) election applies to restricted stock (actual shares), not RSUs. (See our separate post on 83(b) elections and founder equity for that mechanism.)

Founders usually hold actual restricted stock (not options or RSUs) and rely on the 83(b) election to lock in tax treatment at founding — a different mechanism covered in its own post. Employees typically receive ISOs (early), NSOs, or RSUs (later/larger companies). Knowing which bucket you're in tells you which set of rules — and which traps — apply to you.

Practical takeaways

Got ISOs? Model AMT before you exercise, and understand the two holding-period clocks. Early exercise (when the spread is tiny) can minimize AMT — but has its own risks.

Got NSOs? Remember you'll owe ordinary tax on the spread at exercise; have a plan for the cash.

Got RSUs? Budget for an ordinary-income tax hit at vesting, even if you can't sell. Don't count on the gross share value — count the after-tax amount.

Don't forget QSBS. If your shares are in a qualifying C-corp and held long enough, Qualified Small Business Stock can exclude a large chunk of your eventual gain from federal tax — interacting with all of the above.

Coordinate with your personal return. Big equity events can spike your income, trigger AMT, and change estimated-tax obligations. Surprises here are expensive.

The bottom line

ISOs, NSOs, and RSUs are three very different tax animals wearing the same "equity comp" label. The differences — AMT, holding periods, when ordinary income hits, whether you can even sell to pay the tax — decide how much of your equity you actually keep. Before you exercise options or let RSUs vest, run the numbers. The right timing can be the difference between capital-gains rates and a painful ordinary-income bill on money you haven't seen yet.

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Holding startup equity and unsure what you'll owe — or when? Le CPA Group helps employees and founders model exercises, plan around AMT, and time equity decisions. Get in touch for a personalized look, or subscribe for more equity-comp guidance.

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