State Tax Apportionment for RSUs

The Challenge of Mobile Workforces and Deferred Compensation

If you receive Restricted Stock Units (RSUs), stock options, or other forms of deferred compensation, and you live or work in multiple states, determining how much of that income is taxable in each state is a high-stakes calculation. State revenue departments are increasingly aggressive in pursuing their share of this high-value compensation, especially as remote and mobile executive roles become the norm.

Across almost all states with an income tax, the fundamental question is: Where were the services performed that earned this compensation? Because RSUs often vest over several years, the services earning that stock may have been performed in multiple jurisdictions. To divide this income equitably, states use an apportionment formula.

The Baseline: Nuances of the Workday Ratio

The default rule utilized by nearly all state tax authorities (including California, New York, and Massachusetts) is the workday ratio (or duty-day method).

Under this method, the taxable portion of the RSU income in a specific state is determined by a fraction based on the period between the grant date and the vest date:

• Numerator: The total number of days you were physically present and working in that specific state.
• Denominator: The total number of working days everywhere during that same period.

The Denominator Nuance: It is critical to understand how the denominator is calculated. Some states allow for the exclusion of weekends, holidays, and sick days from the denominator, while others may default to total calendar days if your records are unclear. A denominator that includes only "working days" rather than "calendar days" can significantly shift the percentage of income allocated to a state. Without a meticulous daily log that distinguishes between working days, travel days, and personal days, an auditor will likely default to the formula most advantageous to the state.

The "Trailing Liability" Risk

Many taxpayers mistakenly believe that once they move out of a high-tax state, their tax liability to that state ends. For RSU holders, this is a dangerous assumption. States maintain trailing liability: when units vest years after you have relocated, your former state of residence will look back at the entire vesting period. If you worked in that state during any portion of the grant-to-vest period, they will demand their proportional share.

If you stop tracking your locations the moment you move, you lose your ability to accurately calculate the denominator for those later years, making it impossible to defend your apportionment when the tax bill finally arrives years later.

When the Baseline Fails: The "Managing Agent" Concept

While the workday ratio is the standard, there are situations where a simple day count may not accurately reflect how the income was actually earned. This was the central theme in the high-profile Appeal of Prince in California.

In Prince, the taxpayer argued that a simple day count was inequitable because their role and the value they provided to the company changed dramatically over the vesting period. The argument hinges on the "Managing Agent" concept: that an executive's high-level decision-making and increased responsibilities in a new location may be the primary driver of a "sky-rocketing" stock price, rather than routine management performed in a previous state.

Taxpayers may argue for an alternative apportionment method if they can prove that the appreciation in stock value was tied to specific milestones or roles held in specific jurisdictions. However, these "equitable" arguments are technically demanding and require a higher standard of proof.

The Burden of Proof: "Clear and Convincing" Evidence

States presume the standard workday ratio is the most reasonable method. If you wish to deviate from it to optimize your tax position, the burden is entirely on you to provide clear and convincing evidence that the standard formula is unfair.

Auditors do not accept "reconstructed" calendars or "best-guess" estimates. In a residency or apportionment audit, authorities routinely request:

• Cell phone carrier records (tower data);
• Credit card and bank statements showing point-of-purchase locations;
• Travel receipts, boarding passes, and corporate "swipe card" logs.

The most powerful defense is a contemporaneous, GPS-verified log. A log that is created automatically as the days occur carries substantially more weight than a spreadsheet created three years later in response to an audit notice.

Intersection with Special Accrual Rules

For residents of certain states, such as New York, the apportionment of RSUs is further complicated by Special Accrual rules. When a resident changes their domicile, New York may require the "accrual" of certain types of income—including deferred compensation—to the resident period, even if the payment is received later. Navigating the intersection of RSU apportionment and special accrual requires a sophisticated understanding of both sets of rules.
Read more about the New York Special Accrual Rule here.

The Foundation for Optimization: Data is King

Whether you accept the baseline workday ratio or attempt a complex alternative apportionment argument based on changing roles and stock valuations, you cannot optimize what you do not track.

If you lack basic daily location logs to prove exactly when and where you worked during every phase of a multi-year vesting period, your tax strategy will fail. Meticulous day tracking is not just a "good habit"—it is the absolute foundation upon which all RSU tax apportionment and audit defense is built.

Conclusion

Apportioning RSUs and deferred compensation across multiple states requires navigating complex rules. The standard workday ratio is the baseline, but alternatives may exist for executives whose roles and stock values change dramatically. However, no tax strategy can survive without rock-solid evidence of your location history over the multi-year vesting periods.

Download the Domicile365 App to create an automatic, defensible, GPS-based log of your days across all jurisdictions. Signup for a free 60-day trial to start building your foundation for equitable tax apportionment today.