{
  "id": "mortgage-recast",
  "version": "1999e5ee12c0",
  "status": "published",
  "name": "Mortgage Recast Calculator",
  "question": "What will a mortgage recast save?",
  "summary": "Computes the new monthly payment after a lump-sum mortgage recast, the interest it saves, and how it compares with paying the lump sum and keeping the old payment.",
  "category": "finance",
  "subcategory": "loans",
  "url": "https://www.acalculator.org/finance/mortgage-recast-calculator",
  "markdown": "https://www.acalculator.org/finance/mortgage-recast-calculator.md",
  "kind": "schedule",
  "method": "new payment = (B − lump) × r ÷ (1 − (1 + r)^−n), with B the balance, r the rate ÷ 12, and n the months left; old payment is the same formula on B; each plan runs month by month (interest = balance × r).",
  "assumptions": [
    "The rate and the number of months left do not change with the recast.",
    "Today’s payment is the one that repays today’s balance over the months left.",
    "The lump sum is paid now, before the first new payment; the fee is paid in cash, not added to the loan.",
    "Taxes, insurance, and mortgage insurance in the payment are not included.",
    "Values are not rounded to the cent between months; only the display is rounded."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "balance": {
        "title": "Mortgage balance today",
        "description": "The principal you owe today, before the lump sum.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 1000,
        "maximum": 100000000
      },
      "rate": {
        "title": "Interest rate",
        "description": "The mortgage’s fixed yearly rate. A recast keeps it.",
        "type": "number",
        "x-unit": "percent",
        "minimum": 0,
        "maximum": 30
      },
      "left": {
        "title": "Months left to pay",
        "description": "The number of monthly payments left on the mortgage, for example 300 for 25 years.",
        "type": "integer",
        "minimum": 1,
        "maximum": 480
      },
      "lump": {
        "title": "Lump sum",
        "description": "The extra principal you pay before the recast.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0,
        "maximum": 100000000
      },
      "fee": {
        "title": "Recast fee",
        "description": "The fee the servicer charges to recast the loan.",
        "type": "number",
        "x-unit": "USD",
        "minimum": 0,
        "maximum": 100000
      },
      "start": {
        "title": "First payment after the recast",
        "description": "The month of the first new payment. It dates the schedule and the payoff month.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "newPayment": {
      "label": "New monthly payment",
      "description": "The payment after the recast: the balance minus the lump sum, repaid over the months left.",
      "format": "money"
    },
    "oldPayment": {
      "label": "Payment today",
      "description": "The payment that repays today’s balance over the months left.",
      "format": "money"
    },
    "lower": {
      "label": "Lower by",
      "description": "How much less you pay each month after the recast.",
      "format": "money"
    },
    "savedRecast": {
      "label": "Interest saved by recasting",
      "description": "The interest saved compared with no lump sum, when the payment is recast.",
      "format": "money"
    },
    "breakEven": {
      "label": "Months to earn back the fee",
      "description": "How many months of lower payments it takes to cover the recast fee.",
      "format": "integer"
    },
    "savedPrepay": {
      "label": "Interest saved keeping the old payment",
      "description": "The interest saved compared with no lump sum, if you pay the lump sum and keep paying the old amount.",
      "format": "money"
    },
    "sooner": {
      "label": "Months sooner keeping the old payment",
      "description": "How many months earlier the loan ends if you pay the lump sum and keep paying the old amount.",
      "format": "integer"
    },
    "interest": {
      "label": "Interest after the recast",
      "description": "All the interest paid over the months left, after the recast.",
      "format": "money"
    },
    "after": {
      "label": "Balance after the lump sum",
      "description": "Today’s balance minus the lump sum.",
      "format": "money"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "balance": 300000,
      "rate": 6.5,
      "left": 300,
      "lump": 50000,
      "fee": 250,
      "start": "2026-09-29"
    },
    "outputs": {
      "newPayment": 1688.017903369099,
      "oldPayment": 2025.6214840429188,
      "lower": 337.6035806738198,
      "savedRecast": 51281.07420214577,
      "breakEven": 1,
      "savedPrepay": 143645.76099321403,
      "sooner": 95,
      "interest": 256405.3710107302,
      "after": 250000
    },
    "text": "Paying $50,000.00 on $300,000.00 and recasting lowers the payment from $2,025.62 to $1,688.02, saving $51,281.07 of interest."
  },
  "examples": [
    {
      "given": {
        "balance": 300000,
        "rate": 6.5,
        "left": 300,
        "lump": 50000,
        "fee": 250
      },
      "expect": {
        "oldPayment": 2025.621484042925,
        "newPayment": 1688.0179033691043,
        "savedRecast": 51281.07420214589,
        "savedPrepay": 143645.760993212,
        "sooner": 95,
        "breakEven": 1
      },
      "source": "hand calculation in content.mdx; Python 3 in docs/progress/WP-31/python/recast.py"
    },
    {
      "given": {
        "balance": 120000,
        "rate": 0,
        "left": 240,
        "lump": 20000
      },
      "expect": {
        "oldPayment": 500,
        "newPayment": 416.6666666666667,
        "sooner": 40,
        "savedRecast": 0
      },
      "source": "hand calculation in content.mdx: at 0%, 120,000 ÷ 240 and 100,000 ÷ 240; 100,000 ÷ 500 = 200 months"
    },
    {
      "given": {
        "balance": 200000,
        "rate": 7,
        "left": 360,
        "lump": 10000,
        "fee": 500,
        "start": "2026-11-01"
      },
      "expect": {
        "lower": 66.53024951791826,
        "breakEven": 8,
        "savedRecast": 13950.889826451428,
        "sooner": 52
      },
      "source": "hand calculation in content.mdx; Python 3 in docs/progress/WP-31/python/recast.py"
    }
  ],
  "sources": [
    "PNC, What Is a Mortgage Recast? https://www.pnc.com/insights/personal-finance/borrow/what-is-mortgage-recast.html",
    "Consumer Financial Protection Bureau, How does paying down a mortgage work? https://www.consumerfinance.gov/ask-cfpb/how-does-paying-down-a-mortgage-work-en-1943/",
    "Consumer Financial Protection Bureau, What is a prepayment penalty? https://www.consumerfinance.gov/ask-cfpb/what-is-a-prepayment-penalty-en-1957/",
    "Amortized loan payment and number of payments: S. A. Broverman, Mathematics of Investment and Credit, chapter 3."
  ],
  "related": [
    "mortgage",
    "mortgage-payoff",
    "amortization",
    "home-equity-loan"
  ],
  "changelog": []
}