jp mortgage derived

{
  "input": {
    "body": {
      "months": 420,
      "annual_rate": 0.012,
      "principal_yen": 35000000
    },
    "type": "http",
    "method": "POST",
    "bodyType": "json"
  },
  "output": {
    "type": "json",
    "example": {
      "ok": true,
      "note": "SAMPLE RESPONSE generated by the exact deterministic engine that serves production (jp-statutory has no LLM: same input always produces this byte-identical result, carrying the same rules_version and cited primary sources). Served free at /samples/{product} so you can verify the response shape, the rules_version field and the source citations before paying. No payment was taken. The sample_input shown is the catalog example input that produced this output.",
      "tool": "jp-mortgage",
      "as_of": null,
      "result": {
        "method": "level_payment",
        "months_paid": 421,
        "schedule_head": [
          {
            "month": 1,
            "balance_yen": 34932905,
            "payment_yen": 102095,
            "interest_yen": 35000,
            "principal_yen": 67095
          },
          {
            "month": 2,
            "balance_yen": 34865742,
            "payment_yen": 102095,
            "interest_yen": 34932,
            "principal_yen": 67163
          },
          {
            "month": 3,
            "balance_yen": 34798512,
            "payment_yen": 102095,
            "interest_yen": 34865,
            "principal_yen": 67230
          }
        ],
        "schedule_tail": [
          {
            "month": 419,
            "balance_yen": 102149,
            "payment_yen": 102095,
            "interest_yen": 204,
            "principal_yen": 101891
          },
          {
            "month": 420,
            "balance_yen": 156,
            "payment_yen": 102095,
            "interest_yen": 102,
            "principal_yen": 101993
          },
          {
            "month": 421,
            "balance_yen": 0,
            "payment_yen": 156,
            "interest_yen": 0,
            "principal_yen": 156
          }
        ],
        "total_paid_yen": 42880056,
        "total_prepaid_yen": 0,
        "total_interest_yen": 7880056,
        "monthly_payment_yen": 102095
      },
      "sample": true,
      "sources": [
        "deterministic-annuity-math"
      ],
      "summary": "借入35,000,000円・年1.200%・420回 -> 毎月102,095円、総利息7,880,056円",
      "billable": true,
      "breakdown": [],
      "disclaimer": "仮定条件に基づく概算試算。税務相談・手続代行・法律相談ではない。申告・届出への使用不可。確定額は官公署または税理士・社会保険労務士等に確認のこと。",
      "assumptions": [],
      "not_covered": [
        "住宅ローン控除(年度別上限・省エネ区分)",
        "団信・手数料",
        "変動金利の将来予測"
      ],
      "sample_input": {
        "months": 420,
        "annual_rate": 0.012,
        "principal_yen": 35000000
      },
      "rules_version": "2026.08.18",
      "carried_forward": [],
      "unverified_rules": []
    },
    "description": "JSON: monthly payment, total interest, schedule head/tail; prepayment mode returns interest saved + months shortened"
  }
}