Startup equity packages arrive with acronyms, not explanations. This guide covers equity compensation tax planning for RSUs, ISOs, and NSOs, the three most common forms of startup equity, and walks through what happens tax-wise at grant, vesting, exercise, and sale. The tax outcome depends on which type of equity you hold and when each event occurs, so this article treats grant, vesting, exercise, and sale as four distinct events, not interchangeable moments.
“Stock compensation” gets used as a catch-all term, but RSUs, ISOs, NSOs, and restricted stock are taxed under different rules, at different times, sometimes at different rates. Confusing one for another is one of the most expensive mistakes an equity holder can make.
Equity Type | Typical Tax Trigger | Key Planning Issue |
RSUs | Generally vesting/settlement | Ordinary income at the taxable event |
ISOs | Generally exercise and later sale | AMT and holding periods |
NSOs/NQSOs | Generally exercise | Ordinary compensation income on the spread |
Restricted stock | Generally vesting, unless an election applies | 83(b) election timing |
Restricted Stock Units are a company’s promise to deliver actual shares once vesting conditions are met. Unlike stock options, there is no exercise price and no purchase decision involved.
Hypothetical example: an employee receives 1,000 RSUs. At vesting, all 1,000 shares are worth $40 each. Under the general framework, $40,000 may be treated as compensation income at the taxable vesting/settlement event, subject to the plan terms and applicable rules. Shares may be withheld or sold to help cover withholding. The employee’s basis in the remaining shares generally reflects the amount already included in income. A later sale is a separate transaction, producing its own capital gain or loss based on how the price moved after vesting. This example is illustrative only, not personalized tax advice.
Because RSU income arrives on a fixed schedule tied to vesting dates, practical planning tends to focus on:
None of this is investment advice. Whether and when to sell vested shares is a tax and liquidity planning decision, not a recommendation about the stock itself, and employer withholding on RSU income frequently falls short of an employee’s actual final tax liability, particularly for higher earners.
Incentive Stock Options can qualify for favorable federal tax treatment under Section 422 of the Internal Revenue Code, but only if specific statutory requirements are met. ISOs can generally only be granted to employees, not contractors or non-employee directors.
An ISO generally does not create regular federal taxable compensation income at exercise. This is the key distinction from an NSO. However, the spread between the exercise price and fair market value at exercise can still be relevant for Alternative Minimum Tax purposes, and if the stock is sold in the same calendar year it was exercised, that AMT adjustment generally does not apply. Whether the eventual sale receives favorable long-term capital gain treatment depends on satisfying specific ISO holding-period requirements, covered further below.
This is the section that catches the most employees off guard. Exercising an ISO and holding the shares, rather than selling immediately, can generate an AMT adjustment even though no cash changed hands from a sale.
Hypothetical example: an employee exercises 10,000 ISOs at a $5 strike price. The fair market value at exercise is $25 per share. The spread is ($25 minus $5) multiplied by 10,000 shares, or $200,000.
Per current IRS guidance on Form 3921, this $200,000 spread can be an item included in alternative minimum taxable income for the year of exercise, provided the shares are not sold that same year.
This does not mean the employee owes $200,000 in AMT. The actual liability, if any, depends on the taxpayer’s full tax picture, including the AMT exemption amount, other income and deductions, and how the AMT calculation compares to regular tax. What it does mean is that a private-company ISO exercise can create a real cash tax obligation well before there is any way to sell shares to pay for it, which is why modeling this before exercising matters.
This article does not encourage exercising options speculatively based on an anticipated IPO or acquisition. Taxpayers weighing a private-company ISO exercise generally benefit from modeling more than one scenario, including the possibility the shares never become liquid.
Non-qualified stock options, also called nonstatutory stock options, do not need to meet the statutory requirements that apply to ISOs, and can be granted to employees, contractors, advisors, and directors alike.
Hypothetical example: an employee holds 10,000 NSOs with a $5 exercise price. At exercise, fair market value is $25 per share. The $200,000 spread is generally treated as compensation income for federal tax purposes at exercise, subject to withholding, similar in mechanics to wage income. The exercise price plus the amount included in income generally becomes the employee’s basis in the shares. Any further appreciation after exercise, if later sold, may generally produce a separate capital gain or loss, with the holding period beginning at exercise rather than at grant.
Feature | RSUs | ISOs | NSOs/NQSOs |
Grant | Generally no immediate tax | Generally no regular tax at grant | Generally no regular tax at grant |
Vesting | Generally taxable at vesting/settlement | Usually not taxable at vesting | Usually not taxable at vesting |
Exercise | Not applicable | Required, purchase at strike price | Required, purchase at strike price |
Ordinary income at exercise | N/A | Generally none for regular tax, but AMT may apply | Generally yes, on the spread |
AMT | Usually not the central issue | Major planning consideration | Different treatment; not the typical AMT trigger |
Holding period | Begins based on acquisition/basis rules at vesting | Special statutory ISO holding periods apply | Capital-gain holding period generally begins at exercise |
Liquidity concern | Tax can arise before a sale is possible | Significant for private-company shares | Tax at exercise can arise before any sale |
Key planning issue | Withholding adequacy and liquidity | AMT exposure and holding periods | Exercise-time tax and liquidity |
State tax treatment can differ from the federal framework above and is addressed separately later in this article.
A Section 83(b) election is a filing that lets a service provider choose to be taxed on property received in connection with services at the time of transfer, rather than later as it vests. This is generally relevant to restricted stock and similar property subject to a substantial risk of forfeiture, not to standard RSUs. Do not assume an 83(b) election applies to RSUs; RSUs involve a promise of future shares rather than property already transferred and subject to vesting restrictions, so an 83(b) election is generally not applicable to them.
The filing deadline is strict: an 83(b) election must generally be filed within 30 days of the transfer, with no extensions. If the 30th day falls on a weekend or legal holiday, the deadline generally shifts to the next business day. Missing the window is generally treated as a decision not to elect, and that outcome typically cannot be corrected later. As of 2025, the IRS introduced Form 15620, fillable by mail or, for the first time, through an IRS online account, alongside the traditional statement-based method under Treasury Regulation Section 1.83-2.
A timely election can lock in a low current value as the taxable amount and start the capital-gain holding period earlier. The risk: if the shares later decline in value or are forfeited, the tax paid is generally not recoverable in the way the taxpayer expected.
Hypothetical example: a founder receives restricted stock very early in the company’s life, when the shares carry a low current value but remain subject to a multi-year vesting schedule. By filing a timely 83(b) election, the founder can potentially be taxed on that low value at transfer rather than on the presumably higher value at each future vesting date, while also starting the holding-period clock earlier for later capital-gain purposes.
The risk runs the other direction too. If the company’s value later declines substantially, or the shares are forfeited before vesting, the tax the founder paid because of the election is generally not something they can get back. This is a decision that needs analysis before the 30-day deadline, not a default recommendation for every founder or every grant.
To potentially receive favorable long-term capital gain treatment on the full appreciation, ISO shares generally need to be held more than one year after exercise and more than two years after the option was granted.
A sale satisfying both holding-period requirements can potentially receive favorable capital-gain treatment on the appreciation over the exercise price, subject to the taxpayer’s full facts and the AMT analysis already discussed.
A sale before satisfying one or both holding periods is generally a disqualifying disposition. This can result in some or all of the original spread being treated as compensation income rather than capital gain, with any remaining gain treated separately. The exact calculation depends on the sale price relative to the exercise price and fair market value at exercise, and is not reduced to a single formula here.
Usually no immediate tax for standard RSUs or options, subject to award terms and applicable rules.
RSUs generally become taxable at vesting/settlement. Options generally do not become taxable simply by vesting; exercise is the next relevant event.
ISOs may create an AMT adjustment. NSOs generally create ordinary compensation income on the spread. RSUs have no exercise step.
The change in value after the prior taxable event generally produces a capital gain or loss, with the holding period determining short-term versus long-term treatment.
Equity compensation is a common source of underpayment surprises. Payroll withholding on RSU vesting and NSO exercise often uses a flat supplemental wage rate that does not account for the employee’s full marginal tax bracket, other income, or AMT exposure from ISO activity. A large single vesting event, option exercise, or stock sale can each push actual liability well past what was withheld.
Reviewing whether additional estimated payments are needed, per IRS guidance on estimated taxes, is worth doing after any significant equity event rather than waiting until the return is filed. This article does not tell readers to make a specific payment amount without calculating their own full tax situation.
State tax treatment does not automatically mirror the federal framework above. Relevant factors include where you were a resident at grant, vesting, and exercise, where the underlying work was actually performed, whether equity vested while working across more than one state, and how a given state sources or apportions equity income.
Moving to a different state before a liquidity event does not automatically eliminate state tax on equity that vested or was earned while you were a resident of, or working in, the prior state. Multi-state equity compensation, especially for employees who relocated during vesting, generally benefits from specialized analysis rather than a general rule applied uniformly.
Founders sometimes ask about Qualified Small Business Stock under Section 1202, which can potentially exclude a portion of capital gain on qualifying C corporation stock held long enough, subject to a gross-assets test, an active-business requirement, and other conditions. Recent federal legislation adjusted parts of this framework for stock acquired after the law’s effective date, while earlier stock may remain subject to prior rules. Whether a specific company’s stock qualifies is fact-specific and depends on the corporation’s history and the stock’s acquisition date. This is not a promise that any founder’s shares qualify, and it warrants dedicated professional review.
Major liquidity events compress a lot of decisions into a short window. Before a transaction closes, it is worth reviewing:
The planning window is before the transaction closes, not after. This article does not predict whether or when any IPO or acquisition will occur, and does not encourage pursuing a specific transaction.
List every RSU, ISO, NSO, and restricted stock grant, across every employer that issued equity.
Track grant dates, vesting dates, exercise dates, expiration dates, and any completed or planned sale dates.
Model RSU income, NSO spread, ISO AMT exposure, and potential capital gains separately.
Compare what has actually been withheld against a realistic projection of total liability.
Consider residency history and where the underlying services were performed.
Run the numbers for no sale, a partial sale, a full sale, and a range of possible sale prices.
Set aside funds for potential tax liabilities that may come due before shares are liquid.
Equity tax planning works best when coordinated across your stock plan administrator, CPA, a tax attorney where the facts warrant it, an estate attorney where relevant, and a financial adviser where appropriate.
Hypothetical example, for educational purposes only: a startup employee holds 5,000 RSUs, 10,000 ISOs, and 5,000 NSOs, each with different vesting schedules, ahead of a potential liquidity event.
No single tax bill applies to all three types together. Each grant type is analyzed on its own terms, then combined into one overall picture. This example does not calculate a final tax liability for any actual taxpayer.
☐ Grant agreements
☐ Equity award statements
☐ Vesting schedules
☐ Exercise confirmations
☐ Form 3921 for ISO exercises, where applicable
☐ Form 3922 for certain employee stock purchase transactions, where applicable
☐ W-2
☐ 1099-B
☐ Brokerage statements
☐ Cap-table or equity-platform records where relevant
☐ Copy of any 83(b) election filed
☐ Proof of timely 83(b) filing where applicable
☐ Employer withholding records
☐ Stock sale confirmations
☐ Acquisition, IPO, or tender-offer documentation
☐ Prior-year tax returns
☐ Prior-year AMT information
☐ State residency history
NexusWorks put together an Equity Compensation Tax Decision Guide to help readers identify what type of equity they have, when the taxable event is likely to occur, whether exercise is involved, whether AMT may be relevant, whether an 83(b) election may apply, which dates to track, what documents to bring to a CPA, and what questions to ask before exercising or selling.
This is an educational planning tool, not a substitute for individualized tax advice based on your actual grants and full financial picture.
Download the Equity Compensation Tax Decision Guide to start organizing your equity before your next taxable event.
Not every equity holder needs a formal review for every grant. The complexity of your equity mix and the size of the financial impact are what generally justify professional modeling.
NexusWorks helps startup employees, executives, and founders understand the tax implications of their equity compensation before major taxable events occur. This work sits within specialized tax advisory, alongside proactive tax planning, tax filing and compliance, and financial advisory and optimization for concentrated equity positions. Startups coordinating equity plans at the company level can also draw on fractional CFO support.
We do not promise tax savings, a particular AMT outcome, a specific refund, a specific capital-gain rate, favorable treatment tied to a successful IPO or acquisition, or elimination of state tax through relocation. What we can offer is a clear-eyed review of your equity and its tax consequences before you have to make an irreversible decision.
RSUs are generally taxed as ordinary income when they vest and settle into shares, based on fair market value at that time. A later sale creates a separate capital gain or loss based on how the price moved after vesting.
Generally at vesting/settlement, not at grant and not when you eventually sell. Employers typically withhold at vesting, often by withholding a portion of the shares, though this may not cover your full liability.
ISOs generally do not create regular taxable income at exercise, but the spread can be relevant for AMT purposes. A later sale may receive favorable capital-gain treatment if statutory holding periods are met.
The Alternative Minimum Tax adjustment that can arise when you exercise an ISO and hold the shares rather than selling in the same year. The exercise-price-to-FMV spread can be included in AMT income even though no shares were sold.
NSOs generally create ordinary compensation income at exercise, based on the spread between exercise price and fair market value. Later appreciation or depreciation generally produces a separate capital gain or loss at sale.
ISOs can only go to employees, must meet Section 422 requirements, and generally avoid regular income tax at exercise while potentially triggering AMT. NSOs can be granted more broadly and generally create ordinary income at exercise.
A filing that lets a service provider choose to be taxed on property received for services at transfer rather than as it vests. It must generally be filed within 30 days of transfer, with no extensions.
Generally, no. It typically applies to restricted stock and similar property actually transferred and subject to vesting restrictions, not to standard RSUs, which represent a promise of future shares.
Grant agreements, vesting schedules, exercise confirmations, Form 3921 or 3922 where applicable, your W-2 and 1099-B, brokerage statements, any 83(b) election filed, and prior-year returns including AMT information.
It can, but moving does not automatically eliminate tax owed to a state where equity vested or services were performed while you were a resident. Multi-state situations generally need specialized analysis.
