Hometown-tax donation limit (ふるさと納税 控除上限)

How the ceiling is built

The yearly salary is the same salary-only model as the Japan take-home calculator: twelve equal months, no bonus, and 協会けんぽ social insurance for the workplace prefecture. That estimate produces employment income, the income levy of resident tax after the adjustment deduction, and the Reiwa 8 income-tax basic deduction.

The ceiling is the municipal rearrangement. When the special resident-tax piece is exactly 20% of the income levy, the donation is that amount divided by (90% − income-tax rate × 1.021), floored to the yen, plus ¥2,000. The rate comes from the Reiwa 8 base: resident-tax taxable income, minus the personal-deduction gap, minus any income-tax basic deduction above ¥480,000, then floored to ¥1,000.

A donation in calendar 2026 counts toward this ceiling. Income tax is the Reiwa 8 return. Resident tax is the Reiwa 9 assessment, collected from June 2027. One-stop filing (five municipalities or fewer, and no other reason to file) moves the whole benefit onto next year’s resident tax. The planning ceiling is the same.

Formula

What this estimate leaves out

• It is a planning figure. Year-end income is not final, and your city sets the income levy next year.
• Social insurance is the 協会けんぽ employee share from the take-home calculator, not 15% of salary.
• The Reiwa 8 basic deduction, including the extra amount used only for this rate, is included. Many quick tables still use an older deduction.
• Mortgage credit, medical expenses, life-insurance premiums, and iDeCo are not modelled. Each one can cut the usable ceiling.
• The income levy uses the standard 6% city plus 4% prefecture split. Some cities add an extra levy.
• The rate is read from C. The page does not recompute the income-tax bracket after the donation itself.
• From 2027 donations, a ¥1.93 million cap also applies to the special resident-tax deduction. It does not apply to donations made in 2026.

Not in this version

• Choosing a municipality, a gift, or a portal.
• The one-stop application and My Number filing, beyond the note above.
• Self-employment income, retirement income, and other income that is not salary.
• The special spouse deduction, disability, single-parent, working-student, and elderly-dependant cases.