Tax Loss Harvesting Calculator

The Tax Loss Harvesting Calculator simulates the Japanese tax offset system (損益通算/Songeki Tsūsan) for stocks and investment funds. In Japan, capital gains and dividend income from listed stocks are taxed at a flat rate of 20.315% (15.315% income tax + 5% resident tax) under the separate self-assessment taxation system.

When you incur capital losses, you can offset them against capital gains and dividend income from the same year to recover withheld taxes. Moreover, any remaining losses can be carried forward for up to 3 years through filing a tax return (繰越控除/Kurikoshi Kōjo).

This tool calculates your net taxable income, tax savings, and remaining carryforward losses by entering your current year's gains, losses, dividend income, and up to 3 years of prior carryforward losses. It also displays losses expiring this year and a detailed breakdown of which carryforward losses are being used, helping inform your investment decisions.

Use it for pre-filing tax simulations and investment strategy planning. All calculations are performed entirely in your browser — no data is sent to any server.