{
  "address": "73ee86d1f3d837daba5eded55dc45636",
  "category": "other",
  "question": "How much total interest is paid over the life of a $200000 loan at 6% annual interest amortized over 360 months?",
  "answer": "$231,676.00",
  "askedBy": {
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  "answeredBy": "method",
  "madeAt": "2026-09-30T22:39:30.722Z",
  "validUntil": null,
  "validityClass": "forever",
  "sources": [
    {
      "label": "Principles of Corporate Finance",
      "url": null
    }
  ],
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  "supersededBy": null,
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  "answerMethod": "method",
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  "source": {
    "kind": "edition_page",
    "value": "Brealey, Myers, Allen, Principles of Corporate Finance, 13th ed., Chapter 3, section 3-3 (Loan Amortization)",
    "retrieved_utc": "2026-09-30T19:31:29Z"
  },
  "qsha256": "18d246c09491ed91d4d27dbc5bf05c01a89dc9942691d7d4993323d36b67b2f4",
  "runOne": null,
  "cardContractVersion": "card_contract/1",
  "deck_id": "method-deck",
  "deck_title": "Method Deck",
  "method": {
    "name": "Total interest over a loan",
    "version": "1",
    "source_url_or_file": "methods/total-interest-over-loan.cjs",
    "sha256_of_method_file": "cd9918e6055497712e3d4787d3d4a137709b07303e5d44a5793f0398b843f94c"
  },
  "receipt": {
    "inSubstrate": false,
    "local": true,
    "modelCallsAtMint": 0,
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  },
  "method_deck": {
    "inputs": [
      {
        "name": "principal",
        "type": "number",
        "unit": "currency units",
        "required": true,
        "description": "Original loan amount",
        "min": 0
      },
      {
        "name": "annual_rate_percent",
        "type": "number",
        "unit": "%",
        "required": true,
        "description": "Nominal annual interest rate, compounded monthly",
        "min": 0
      },
      {
        "name": "months",
        "type": "integer",
        "required": true,
        "description": "Number of monthly payments (loan term in months)",
        "min": 1
      }
    ],
    "outputs": [
      {
        "name": "monthly_payment",
        "unit": "currency units",
        "description": "Fixed monthly payment"
      },
      {
        "name": "total_paid",
        "unit": "currency units",
        "description": "Sum of all payments over the loan"
      },
      {
        "name": "total_interest",
        "unit": "currency units",
        "description": "Total interest paid over the loan"
      }
    ],
    "steps": [
      "Convert the annual rate to a decimal: r = annual_rate_percent / 100; monthly rate i = r / 12.",
      "Compute the fixed monthly payment using the standard annuity formula: payment = principal * i * (1+i)^months / ((1+i)^months - 1) (or principal/months if i = 0).",
      "total_paid = payment * months.",
      "total_interest = total_paid - principal.",
      "Round monthly_payment, total_paid, and total_interest to 2 decimals (money to cents)."
    ],
    "constants": [],
    "examples": [
      {
        "name": "worked example",
        "inputs": {
          "principal": 200000,
          "annual_rate_percent": 6,
          "months": 360
        },
        "expected": {
          "answer": "$231,676.00"
        },
        "check": "hand computation: payment = 1199.10 (see loan-payment-amortized), total_paid = 1199.10*360 = 431676.00, total_interest = 431676.00-200000 = 231676.00"
      },
      {
        "name": "test vector: zero interest",
        "inputs": {
          "principal": 12000,
          "annual_rate_percent": 0,
          "months": 12
        },
        "expected": {
          "answer": "$0.00"
        },
        "check": "hand computation: payment = 1000.00, total_paid = 12000.00, total_interest = 0.00"
      }
    ],
    "disclaimer": null,
    "deck_category": "finance"
  },
  "status": "minted",
  "kind": "method",
  "provenanceClass": "own_question",
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    "chain": [
      {
        "source": {
          "kind": "edition_page",
          "value": "Brealey, Myers, Allen, Principles of Corporate Finance, 13th ed., Chapter 3, section 3-3 (Loan Amortization)",
          "retrieved_utc": "2026-09-30T19:31:29Z"
        },
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        "supersedes": null,
        "added_utc": "2026-09-30T22:39:30.722Z",
        "added_by": "method:Total interest over a loan",
        "why": "the method that computed this answer",
        "check": null,
        "status_label": "pending",
        "signature": null
      }
    ]
  }
}