As a US citizen, you owe US tax on worldwide income no matter where you live — including capital gains from selling stock held through a non-US broker in Japan. Enter your other income and the gain to estimate your US federal tax.
US Capital Gains Tax Calculator
Estimate US federal tax on long-term gains from selling foreign stock, as an American living in Japan
For stock held more than 1 year. Short-term gains are taxed as ordinary income and aren’t covered by this calculator.
* 2026 IRS thresholds. Estimates federal tax only — state tax, if any, and the specific mechanics of the Foreign Tax Credit against Japanese tax on the same gain aren’t included.
How to Use
- Select your filing status.
- Enter your other taxable income for the year, not counting this gain.
- Enter the long-term capital gain from this sale (stock held more than 1 year).
- Click Calculate to see the capital gains tax, the Net Investment Income Tax if it applies, and your total estimated US federal tax.
How the calculation works
Long-term capital gains “stack” on top of your other taxable income and are taxed at 0%, 15%, or 20% depending on which bracket that income falls into. If your modified adjusted gross income exceeds $200,000 (single) or $250,000 (MFJ), an additional 3.8% Net Investment Income Tax applies to the lesser of your investment income or the amount over the threshold.
2026 brackets — Single: 0% up to $49,450, 15% up to $545,500, 20% above
Married Filing Jointly: 0% up to $98,900, 15% up to $613,700, 20% above
For how Japan separately taxes the same gain and how the two interact, see How Japan Taxes Your Overseas Stock Gains.
Frequently Asked Questions
Q. Why do US citizens in Japan owe US tax on a Japan-based brokerage sale?
A. The US taxes citizens on worldwide income regardless of where they live — this is citizenship-based taxation, unlike most countries which tax based on residency only.
Q. Does this account for Japanese tax on the same gain?
A. No. Japan separately taxes the gain, and a Foreign Tax Credit may reduce double taxation, but the specific credit mechanics aren’t modeled in this simplified calculator.
Q. What if I held the stock for less than a year?
A. Short-term gains (held 1 year or less) are taxed as ordinary income at your regular tax bracket, not at the preferential long-term rates this calculator uses.
Key Takeaways
- US citizens owe US tax on worldwide capital gains regardless of residence.
- Long-term gains are taxed at 0%, 15%, or 20% depending on your total taxable income.
- An extra 3.8% NIIT applies above $200,000 (single) / $250,000 (MFJ) MAGI.