How RSUs, ISOs, ESPPs, and NSOs Are Sourced for Tax Purposes: Key Similarities and Differences

When you receive equity compensation and have lived or worked in multiple jurisdictions (whether states or countries), determining where your income is taxable—also known as income sourcing—is crucial. Each type of equity award is taxed differently, and the rules for allocating that income across jurisdictions can vary based on the type of award and timing.

This guide explains the key similarities and differences in sourcing rules for four common types of equity compensation:

  • Restricted Stock Units (RSUs)

  • Incentive Stock Options (ISOs)

  • Employee Stock Purchase Plans (ESPPs)

  • Non-Qualified Stock Options (NSOs)

What Is Income Sourcing?

Income sourcing refers to how income from equity compensation is allocated to various jurisdictions for tax purposes. This affects whether a country or state can tax you on that income and whether you can claim a foreign tax credit, which is particularly important if you’ve:

  • Moved states or countries during the vesting or holding periods, or

  • Worked for a global company while working internationally.

Why Sourcing Matters

  • You could owe state or international tax even if you don’t live there when the equity vests, is exercised, or sold.

  • Different jurisdictions have different sourcing periods (e.g., grant-to-vest vs. vest-to-exercise).

  • Poor documentation can lead to double taxation or missed deductions.

  • High-income equity events (IPOs, liquidity events) can trigger audits if sourcing isn't done correctly.

RSUs: Grant-to-Vesting Sourcing

RSUs are the simplest in terms of sourcing. Since they are taxed as ordinary income when they vest, the income is generally sourced based on where you performed the work during the grant-to-vest period.

  • If you moved during the vesting period, multiple jurisdictions may claim a portion.

  • Example: The RSUs vested while you were working and a resident of the US. 50% of the RSU vesting period was spent working in Canada and 50% in the United States, Canada may claim tax on 50% of the RSU income. The US would report 100% of the RSU income and you would be able to claim a foreign tax credit (up to the US effective rate) on the Canada source portion (50%).

Many foreign countries apply similar rules, but specific methods can vary.

ISOs: Alternative Minimum Tax & Sourcing

ISOs are not taxed at grant or exercise under regular U.S. tax rules, though they can trigger AMT.

ISOs offer favorable tax treatment under U.S. tax law, but can introduce complexity, especially when:

  • You exercise ISOs while living or working abroad

  • You’re subject to AMT (Alternative Minimum Tax)

  • You pay foreign income tax on the ISO income and want to claim a Foreign Tax Credit (FTC)

AMT Income Is U.S.-Sourced by Default, but Exceptions Exist

  • By default, the IRS treats ISO AMT income as U.S.-sourced because the income arises from a U.S. statutory tax preference item.

  • However, you can allocate (source) this income between countries if services were performed outside the U.S. between grant and vest.

When shares are sold:

  • If it’s a qualified disposition, gains are taxed as long-term capital gains and typically not sourced based on where the work occurred.

  • If it’s a disqualified disposition (e.g. sold too early), part of the gain becomes ordinary income, and sourcing may apply—usually using the grant-to-vest period.

Foreign tax authorities may not recognize ISOs and could treat them similarly to NSOs, taxing the bargain element at exercise.

ESPPs: Grant-to-Purchase Sourcing

For qualified ESPPs, taxation occurs only at sale, and part of the income is treated as ordinary income based on the discount at purchase. The sourcing of that income generally reflects:

  • The grant-to-purchase period—i.e., the time during which you were making contributions and earning the right to buy the stock at a discount.

Some countries (and U.S. states) may alternatively use the purchase-to-sale period for sourcing capital gains, but the ordinary income component is most commonly sourced over grant-to-purchase.

Because ESPPs typically have multiple offering and purchase dates, you may need to track and source each lot separately.

NSOs: Grant-to-Vest

NSOs are taxed in two phases:

  1. At exercise (ordinary income on the bargain element)

  2. At sale (capital gain)

For sourcing purposes, the income at exercise is typically sourced over the grant-to-vest period—especially for U.S. federal tax purposes and many state and international systems.

Non-employee NSOs (e.g. contractors) may have different sourcing and reporting rules.

International & State Tax Coordination

If you've moved between states or countries while equity was vesting or being held:

  • Even if you’re no longer working/living there, each jurisdiction may tax a pro-rata share of the income based on days worked.

  • Double taxation is possible, especially if one country taxes at vesting and another at sale.

  • Tax treaties and foreign tax credits may offer relief—but applying them correctly requires careful coordination and documentation.

Best Practices for Managing Equity Compensation Sourcing (RSUs, ISOs, NSOs, ESPPs)

Whether you're receiving stock grants, options, or participating in an ESPP, sourcing rules can significantly impact your tax liability—especially if you’ve lived or worked in multiple jurisdictions. Use the following best practices to stay ahead:

Track Key Dates and Events

  • Record grant, vesting, exercise, and sale dates for each award.

  • Maintain a timeline that aligns with your work locations during each period.

Document Where You Worked

  • Keep a detailed location log showing where you performed services throughout the equity lifecycle.

  • If you moved across states or countries, note exact dates of relocation and work performed in each place.

Keep Supporting Documents

  • Save grant agreements, vesting schedules, brokerage confirmations, and W-2s.

  • For international cases, keep foreign payslips and proof of tax residency or work permits.

Review Your Employer's Reporting

  • Check your W-2 or foreign equivalents to ensure income sourcing is accurate.

  • If it’s not prorated correctly (e.g., 100% sourced to a state you left months ago), you may need to file adjustments.

Plan Ahead for Exercises and Sales

  • Consider the tax impact of location before exercising or selling equity.

  • In high-tax jurisdictions (e.g., CA, NY), income may be sourced there even if you've moved—timing matters.

Mitigate Double Taxation

  • Understand how to use foreign tax credits or state credit mechanisms to avoid being taxed twice on the same income.

  • Leverage tax treaties or consult advisors for special international cases.

Work with a Cross-Border Tax Advisor

  • Especially important if you’re:

    • Working remotely across borders

    • Transitioning between states or countries

    • Facing a large liquidity event (e.g., IPO, tender offer)

By staying organized, documenting your history, and proactively managing sourcing issues, you’ll reduce audit risk and potentially save thousands in unnecessary taxes.

Need help applying this to your situation? Zeisei Group specializes in equity compensation for globally mobile professionals—get in touch to learn more.