Most Japanese employees assigned to the United States are covered by a company tax equalization policy. The pay slip shows a deduction labeled hypothetical tax, the employer pays the U.S. income tax, and yet the Form W-2 shows a figure far larger than the salary and the tax return is full of unfamiliar numbers. Without understanding the mechanics, the year-end equalization settlement and the treatment of personal income can be confusing. This article explains how tax equalization and gross-ups work, why employer-paid tax is taxable compensation, how it flows into the W-2, and what assignees themselves must still take care of. Rules are as of 2026.
The Idea Behind Tax Equalization: Pay Only What You Would Have Paid at Home
Tax equalization is designed so that an assignment neither increases nor decreases the employee’s tax burden. The employee has a hypothetical tax deducted from pay, approximating the Japanese income and inhabitant taxes he or she would have paid by staying in Japan, and in exchange the company pays the actual U.S. federal, state, and city taxes. A related approach, tax protection, reimburses the employee only when the U.S. tax exceeds the home-country tax, and lets the employee keep any savings.
- Hypothetical tax is usually computed on company-paid compensation such as base salary and bonus. Most policies exclude personal investment income and a spouse’s income.
- The company typically covers federal income tax, state income tax (and city tax in New York City), and sometimes social security taxes, but not tax on the employee’s personal income such as dividends, rental income, or cryptocurrency.
- After the return is prepared, the actual tax is compared with the hypothetical tax withheld during the year and the difference is settled between the company and the employee.
Employer-Paid Tax Is Wages: How the Gross-Up Works
Under U.S. tax law, tax paid by an employer on an employee’s behalf is additional compensation to the employee. If the company pays $10,000 of tax, that $10,000 is itself taxable; if the company pays that tax too, the cycle continues. A gross-up calculates the compensation needed so that, after tax, the employee is left with the intended amount. For an assignee with a combined federal and state marginal rate of 40%, covering $6,000 of tax requires additional grossed-up compensation of $6,000 divided by (1 minus 0.4), or $10,000.
What appears on the W-2
Box 1 taxable wages for an equalized assignee are built up roughly as follows:
| Item | Treatment on the W-2 |
|---|---|
| Base salary and bonus (U.S.-paid and Japan-paid combined) | Included in taxable wages |
| Hypothetical tax deducted from pay | Reduces taxable wages (treated as a reduction of compensation) |
| Employer-paid federal, state, and city taxes, including the gross-up | Included in taxable wages |
| Housing allowance, cost-of-living adjustment, home leave, children’s tuition, personal use of a company car | Included in taxable wages |
| Employer-paid moving expenses | Included (since 2018; made permanent by the OBBBA, except for military and similar personnel) |
| Employer-paid tax return preparation fees | Included in taxable wages |
| Employer-provided health insurance, retirement plan contributions within limits | Excluded from taxable wages |
Japan-paid salary must also be reported. A U.S. tax resident (a green card holder or someone meeting the substantial presence test) is taxed on worldwide income, so any Japan-paid compensation not already on the W-2 has to be added on the return. Many Japanese employers prepare a gross-up worksheet that reflects Japan-paid amounts and employer-paid taxes and either issue the W-2 on that basis or provide the figures for the return. Salary differential payments made by the Japanese parent company are deductible for the parent in Japan but are taxable compensation to the assignee in the United States.
Social Security Taxes and the U.S.-Japan Totalization Agreement
An employee who remains in the Japanese pension system and is sent to the U.S. for an expected period of five years or less can obtain a certificate of coverage from the Japan Pension Service under the U.S.-Japan Social Security Agreement and is then exempt from U.S. Social Security and Medicare taxes (the employee share is 6.2% and 1.45%, with the 2026 Social Security wage base at $184,500). Without the certificate, or when the assignment exceeds five years, U.S. FICA applies, and whether the company grosses it up depends on the policy.
What the Assignee Must Still Handle
- You are legally responsible for the return even when the company’s accounting firm prepares it. Review it carefully and provide complete information on Japanese rental income, dividends, cryptocurrency, and Japanese financial accounts.
- Tax on personal income is normally yours to pay. Because it is outside the hypothetical tax, the year-end settlement may require you to pay the company back. Items such as Japanese mutual funds, which may be PFICs requiring Form 8621, call for your own attention.
- The FBAR and Form 8938 are personal obligations unrelated to the company policy. If the combined balance of your Japanese accounts exceeds $10,000, an FBAR is required.
- State residency: New York State and City and California apply strict residency tests. Check whether state and city taxes are within the scope of the policy.
- Business travelers are different: for temporary trips expected to last one year or less, employer-paid lodging and meals can be excludable travel expenses, but that treatment does not apply to an assignee whose U.S. post has become the regular place of work.
Frequently Asked Questions
Is hypothetical tax deductible or creditable on my U.S. return?
No. Hypothetical tax is not a tax actually paid to any government; it is a compensation adjustment between you and your employer. It is reflected as a reduction of W-2 wages and nothing more.
Why does the year-end settlement say I owe money to the company?
This happens when the hypothetical tax withheld during the year was less than the recomputed stay-at-home tax under the policy, or when the company advanced tax on personal income that the policy assigns to you. Review the settlement worksheet to see which income was treated as company-covered and which as your responsibility.
Can I still owe U.S. tax after I return to Japan?
Yes. RSUs or stock options granted during the assignment that vest or are exercised after repatriation are partly U.S.-source income for the U.S. workdays and may require a Form 1040-NR. Many companies continue to equalize this trailing income for several years after the assignment ends.
This article is provided for general informational purposes only and does not constitute individual tax advice. Please review current IRS rules and your employer’s policy, and consult a qualified U.S. tax professional before acting.
Summary
Tax equalization keeps an assignee’s tax burden at the level it would have been in Japan, and the U.S. taxes the company pays are grossed up and added to the assignee’s taxable compensation. That is why the W-2 is so large, and why the hypothetical tax appears as a reduction of wages rather than a tax. Personal investment income and foreign account reporting remain your own responsibility, so understanding where the policy stops and your obligations begin is the best way to avoid settlement disputes and missed filings.
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