What the calculator estimates
The result is the largest donation estimated to remain within the standard Furusato Nozei relief rules, apart from the annual ¥2,000 personal cost. Planning mode derives taxable-income and resident-tax figures from projected inputs. Tax-figures mode uses values supplied from tax documents for a more direct estimate.
The three relief components
- Income-tax deduction: the eligible donation amount multiplied by the applicable income-tax rate and the 2.1% reconstruction surtax.
- Resident-tax basic credit: generally 10% of the eligible donation amount.
- Resident-tax special credit: the remaining statutory percentage, capped at 20% of the resident-tax income levy.
The calculator also tests the broader income-tax and resident-tax donation ceilings. The lowest applicable ceiling controls the result.
Tax year and rounding
The current model is labeled for calendar year 2026. It includes the 2026 income-tax brackets and the applicable basic and salary-income deduction model used by this calculator. Intermediate tax bases and the final recommendation are rounded conservatively to reflect how Japanese tax calculations use prescribed units.
Planning assumptions
Planning mode assumes the standard combined 10% resident-tax income levy and asks the user to supply social insurance and other relevant deductions. The default recommendation applies a 5% safety buffer because final income and deductions can change before year end.
Where this method is not sufficient
Professional review is appropriate for substantial business, property, capital-gains or overseas income; carried losses; home-loan tax credits; unusual local tax rates; very high income; major mid-year changes; or any case where the tax treatment is uncertain.