Rating uses two axes: housing-cost ratio (after-tax basis) × monthly surplus. ◎ Safe <30% / ○ Sound 30–40% (or 40–50% with ample surplus) / △ Caution / × Reconsider
Social insurance is an estimate (Kyokai Kenpo Tokyo health insurance, employee pension, employment insurance, long-term care for age 40+). Bonus portions apply the standard-bonus caps (health ¥5.73M/yr, pension ¥1.5M/payment).
Social insurance on variable pay (commission, etc.) is estimated assuming bonus-style payment. Unlike income tax, social insurance is not reconciled at year-end; premiums are fixed separately on salary and on each bonus (each with its own cap), so the total varies with how pay is split.
Income tax includes the special reconstruction surtax (base income tax × 2.1%). Residential tax is the 10% income levy plus a ¥5,000 per-capita levy.
The income-adjustment deduction (cap ¥150k) applies when income exceeds ¥8.5M with a dependent under 23 (approximated as dependents ≥ 1).
The spousal deduction applies only when the spouse meets the income requirement; in dual-income / pair-loan mode it is automatically excluded.
Mortgage tax credit: 0.7% of year-end balance; the portion not offset against income tax is credited against residential tax up to ¥97,500. Excluded if total income exceeds ¥20M.
The basic deduction phases out above ¥24M total income. The spousal deduction is excluded above ¥10M total income.
Post-retirement income is entered directly as after-tax monthly take-home (combine pension, severance, asset drawdown, etc.).
The deferred-lump-sum option approximates SBI Sumishin Net Bank's "deferred-lump-sum hybrid mortgage" (modeled with appraised value ≈ property price). The lump sum at term end must be settled via sale, refinancing, or own funds.
The 1.25× payment-cap rule is not modeled. Living costs assume 1.5% annual inflation (education & car costs are flat). This is an approximate simulation.
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