{
  "$comment": "Machine-readable companion to https://valem.run/calculators/tools/debt-payoff. Formula, inputs, outputs, engine-verified test vectors, cited sources and the re-runnable Valem ModelSpec behind the page.",
  "url": "https://valem.run/calculators/tools/debt-payoff",
  "dataUrl": "https://valem.run/calculators/tools/debt-payoff.json",
  "license": {
    "name": "CC BY 4.0",
    "url": "https://creativecommons.org/licenses/by/4.0/",
    "attribution": "Decision tools debt payoff planner model by Valem (https://valem.run/calculators/tools/debt-payoff), CC BY 4.0.",
    "note": "Covers the model — the expression of each rule and the arrangement of the catalog. The rates and thresholds themselves are law and are not licensed by anyone; the cited sources are where they come from."
  },
  "verificationUrl": "https://valem.run/calculators/tools/debt-payoff/verify",
  "country": "tools",
  "countryName": "Decision tools",
  "formula": "debt-payoff",
  "formulaName": "Debt payoff planner",
  "title": "Debt Payoff Calculator — snowball vs avalanche",
  "answer": "The avalanche method — paying the highest interest rate first — always costs less in interest than the snowball method, which pays the smallest balance first; the snowball’s advantage is motivational, and this model prices exactly what that motivation costs.",
  "lang": "en",
  "currency": "USD",
  "taxYear": "",
  "verification": {
    "claim": "internal-consistency",
    "statement": "The Valem engine reproduces this model's stated formula through 3 self-test cases (below, and re-runnable against the spec). That asserts internal consistency, NOT that the formula matches current law — the cited sources are the evidence for that, and carry the date each was last checked.",
    "selfTestCases": 3,
    "ratesAreIllustrative": false,
    "sourcesCheckedOn": "2026-08-02"
  },
  "sources": [],
  "terminalOutput": "schedule",
  "inputs": [
    {
      "name": "debts",
      "type": "array",
      "label": "Your debts"
    },
    {
      "name": "monthlyBudget",
      "type": "number",
      "label": "Total you can pay each month",
      "minimum": 0
    },
    {
      "name": "strategy",
      "type": "string",
      "label": "Which debt gets the extra money",
      "enum": [
        "avalanche",
        "snowball"
      ]
    }
  ],
  "outputs": [
    {
      "name": "totalBalance",
      "type": "number",
      "label": "Total owed today",
      "format": "number",
      "formula": "$round($sum($map(debts, function($d) { $d.balance })), 2)"
    },
    {
      "name": "totalMinimums",
      "type": "number",
      "formula": "$round($sum($map(debts, function($d) { $d.minPayment })), 2)"
    },
    {
      "name": "avalanche",
      "type": "object",
      "formula": "$simulate($sort(debts, function($x, $y) { $x.aprPct < $y.aprPct }), monthlyBudget, $const.maxMonths)"
    },
    {
      "name": "snowball",
      "type": "object",
      "formula": "$simulate($sort(debts, function($x, $y) { $x.balance > $y.balance }), monthlyBudget, $const.maxMonths)"
    },
    {
      "name": "monthsToFree",
      "type": "integer",
      "label": "Months to debt free",
      "format": "number",
      "formula": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.months )"
    },
    {
      "name": "totalInterest",
      "type": "number",
      "label": "Interest you pay",
      "format": "number",
      "formula": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.interest )"
    },
    {
      "name": "payoffOrder",
      "type": "string",
      "formula": "( $s := strategy = \"snowball\" ? snowball : avalanche; $join($s.order, \" → \") )"
    },
    {
      "name": "interestSaved",
      "type": "number",
      "label": "Avalanche saves",
      "format": "number",
      "formula": "( $s := snowball; $a := avalanche; $round($s.interest - $a.interest, 2) )"
    },
    {
      "name": "clearsInHorizon",
      "type": "boolean",
      "formula": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.cleared )"
    },
    {
      "name": "schedule",
      "type": "array",
      "label": "What you still owe, month by month",
      "formula": "( $s := strategy = \"snowball\" ? snowball : avalanche; [$s.history] )"
    }
  ],
  "testCases": [
    {
      "description": "three debts totalling 11,500 on a 600 budget, avalanche — highest rate first",
      "given": {
        "monthlyBudget": 600,
        "strategy": "avalanche"
      },
      "expect": {
        "totalBalance": 11500,
        "totalMinimums": 265,
        "monthsToFree": 23,
        "totalInterest": 1509.23,
        "clearsInHorizon": true,
        "interestSaved": 112.56,
        "schedule[0].interest": 142.5,
        "schedule[0].balance": 11042.5,
        "schedule[22].balance": 0
      }
    },
    {
      "description": "the same debts on snowball — clears in the same 23 months but costs 112.56 more in interest",
      "given": {
        "monthlyBudget": 600,
        "strategy": "snowball"
      },
      "expect": {
        "monthsToFree": 23,
        "totalInterest": 1621.79,
        "interestSaved": 112.56
      }
    },
    {
      "description": "paying only the minimums stretches it to 66 months and nearly quadruples the interest",
      "given": {
        "monthlyBudget": 265,
        "strategy": "avalanche"
      },
      "expect": {
        "monthsToFree": 66,
        "totalInterest": 5876.6,
        "interestSaved": 30.42,
        "clearsInHorizon": true
      }
    }
  ],
  "spec": {
    "id": "debt-payoff",
    "version": "1.0.0",
    "schema": {
      "type": "object",
      "properties": {
        "debts": {
          "type": "array",
          "minItems": 1,
          "maxItems": 8,
          "items": {
            "type": "object",
            "properties": {
              "name": {
                "type": "string"
              },
              "balance": {
                "type": "number",
                "minimum": 0
              },
              "aprPct": {
                "type": "number",
                "minimum": 0,
                "maximum": 60
              },
              "minPayment": {
                "type": "number",
                "minimum": 1
              }
            }
          }
        },
        "monthlyBudget": {
          "type": "number",
          "minimum": 0,
          "description": "Total you can put toward debt each month"
        },
        "strategy": {
          "type": "string",
          "enum": [
            "avalanche",
            "snowball"
          ]
        },
        "totalBalance": {
          "type": "number",
          "readOnly": true
        },
        "totalMinimums": {
          "type": "number",
          "readOnly": true
        },
        "avalanche": {
          "type": "object",
          "readOnly": true
        },
        "snowball": {
          "type": "object",
          "readOnly": true
        },
        "monthsToFree": {
          "type": "integer",
          "readOnly": true
        },
        "totalInterest": {
          "type": "number",
          "readOnly": true
        },
        "payoffOrder": {
          "type": "string",
          "readOnly": true
        },
        "interestSaved": {
          "type": "number",
          "readOnly": true,
          "description": "What avalanche saves against snowball on these debts"
        },
        "clearsInHorizon": {
          "type": "boolean",
          "readOnly": true
        },
        "schedule": {
          "type": "array",
          "readOnly": true,
          "items": {
            "type": "object",
            "properties": {
              "month": {
                "type": "integer"
              },
              "balance": {
                "type": "number"
              },
              "interest": {
                "type": "number"
              }
            }
          }
        }
      },
      "required": [
        "debts",
        "monthlyBudget"
      ]
    },
    "constants": {
      "maxMonths": 120
    },
    "library": {
      "layers": [
        {
          "define": "( $monthStep := function($rows, $budget) { ( $grown := $map($rows, function($r) { ( $acc := $r.balance <= 0 ? 0 : $round($r.balance * $r.aprPct / 1200, 2); $nb := $round($r.balance + $acc, 2); $merge([$r, {\"accrued\": $acc, \"balance\": $nb, \"due\": $nb <= 0 ? 0 : $min([$r.minPayment, $nb])}]) ) }); $surplus := $max([0, $budget - $sum($grown.due)]); $alloc := $reduce($grown, function($s, $r) { ( $extra := ($r.balance > 0 and $s.hit = false) ? $min([$s.rem, $r.balance - $r.due]) : 0; { \"rem\": $s.rem - $extra, \"hit\": $s.hit or $r.balance > 0, \"out\": $append($s.out, [$merge([$r, {\"balance\": $round($r.balance - $r.due - $extra, 2)}])]) } ) }, {\"rem\": $surplus, \"hit\": false, \"out\": []}); { \"rows\": [$alloc.out], \"interest\": $round($sum($grown.accrued), 2), \"paid\": $round($sum($grown.due) + ($surplus - $alloc.rem), 2) } ) }; $simulate := function($ordered, $budget, $maxMonths) { ( $r := $reduce([1..$maxMonths], function($a, $m) { $a.done ? $a : ( $step := $monthStep($a.rows, $a.budget); { \"rows\": $step.rows, \"budget\": $a.budget, \"interest\": $round($a.interest + $step.interest, 2), \"paid\": $round($a.paid + $step.paid, 2), \"months\": $m, \"done\": $sum($step.rows.balance) <= 0, \"history\": $append($a.history, [{\"month\": $m, \"balance\": $round($sum($step.rows.balance), 2), \"interest\": $step.interest}]) } ) }, {\"rows\": [$ordered], \"budget\": $budget, \"interest\": 0, \"paid\": 0, \"months\": 0, \"done\": false, \"history\": []}); { \"order\": [$map($ordered, function($d) { $d.name })], \"months\": $r.months, \"interest\": $r.interest, \"paid\": $r.paid, \"cleared\": $r.done, \"history\": [$r.history] } ) }; [\"monthStep\", \"simulate\"] )"
        }
      ]
    },
    "defaultValues": [
      {
        "path": "$",
        "expr": "{\"debts\": [{\"name\": \"Store card\", \"balance\": 500, \"aprPct\": 6, \"minPayment\": 25}, {\"name\": \"Credit card\", \"balance\": 3000, \"aprPct\": 24, \"minPayment\": 60}, {\"name\": \"Car loan\", \"balance\": 8000, \"aprPct\": 12, \"minPayment\": 180}], \"monthlyBudget\": 600, \"strategy\": \"avalanche\"}"
      }
    ],
    "derivations": [
      {
        "path": "$.totalBalance",
        "expr": "$round($sum($map(debts, function($d) { $d.balance })), 2)"
      },
      {
        "path": "$.totalMinimums",
        "expr": "$round($sum($map(debts, function($d) { $d.minPayment })), 2)"
      },
      {
        "path": "$.avalanche",
        "expr": "$simulate($sort(debts, function($x, $y) { $x.aprPct < $y.aprPct }), monthlyBudget, $const.maxMonths)"
      },
      {
        "path": "$.snowball",
        "expr": "$simulate($sort(debts, function($x, $y) { $x.balance > $y.balance }), monthlyBudget, $const.maxMonths)"
      },
      {
        "path": "$.monthsToFree",
        "expr": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.months )"
      },
      {
        "path": "$.totalInterest",
        "expr": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.interest )"
      },
      {
        "path": "$.clearsInHorizon",
        "expr": "( $s := strategy = \"snowball\" ? snowball : avalanche; $s.cleared )"
      },
      {
        "path": "$.payoffOrder",
        "expr": "( $s := strategy = \"snowball\" ? snowball : avalanche; $join($s.order, \" → \") )"
      },
      {
        "path": "$.interestSaved",
        "expr": "( $s := snowball; $a := avalanche; $round($s.interest - $a.interest, 2) )"
      },
      {
        "path": "$.schedule",
        "expr": "( $s := strategy = \"snowball\" ? snowball : avalanche; [$s.history] )"
      }
    ],
    "constraints": [
      {
        "id": "budget-covers-minimums",
        "expr": "monthlyBudget >= totalMinimums",
        "message": "Your monthly budget is below the total of the minimum payments — the balances would grow rather than fall",
        "policy": "flag"
      },
      {
        "id": "has-a-debt",
        "expr": "$count(debts) >= 1",
        "message": "Add at least one debt",
        "policy": "rollback"
      }
    ],
    "viewDefinition": {
      "renderer": "builtin",
      "defaultView": "main",
      "views": [
        {
          "id": "main",
          "label": "Debt payoff",
          "layout": "vertical",
          "components": [
            {
              "id": "assumptions",
              "type": "alert",
              "variant": "info",
              "label": "This is a projection from your assumptions",
              "text": "The simulation charges interest monthly, pays every minimum, and throws whatever is left at one debt at a time. It assumes you never miss or change a payment and that no new borrowing happens. Both strategies are run on the same numbers, so the comparison between them is exact even where the absolute months are not."
            },
            {
              "id": "debtsList",
              "type": "sectionList",
              "label": "Your debts",
              "bind": "$.debts",
              "itemView": "debtItem",
              "addLabel": "Add a debt",
              "removeLabel": "Remove"
            },
            {
              "id": "planSet",
              "type": "fieldSet",
              "legend": "Your plan",
              "components": [
                {
                  "id": "budgetField",
                  "type": "numericField",
                  "label": "Total you can pay each month",
                  "bind": "$.monthlyBudget",
                  "placeholder": "600"
                },
                {
                  "id": "strategyField",
                  "type": "radioField",
                  "label": "Which debt gets the extra money",
                  "bind": "$.strategy",
                  "options": [
                    {
                      "value": "avalanche",
                      "label": "Avalanche — highest interest rate first (cheapest)"
                    },
                    {
                      "value": "snowball",
                      "label": "Snowball — smallest balance first (fastest first win)"
                    }
                  ]
                }
              ]
            },
            {
              "id": "sep1",
              "type": "separatorLine"
            },
            {
              "id": "headline",
              "type": "group",
              "layout": "horizontal",
              "components": [
                {
                  "id": "monthsTile",
                  "type": "statTile",
                  "label": "Months to debt free",
                  "bind": "$.monthsToFree",
                  "format": "number"
                },
                {
                  "id": "interestTile",
                  "type": "statTile",
                  "label": "Interest you pay",
                  "bind": "$.totalInterest",
                  "format": "number"
                },
                {
                  "id": "savedTile",
                  "type": "statTile",
                  "label": "Avalanche saves",
                  "bind": "$.interestSaved",
                  "format": "number",
                  "caption": "vs snowball, same budget"
                },
                {
                  "id": "balanceTile",
                  "type": "statTile",
                  "label": "Total owed today",
                  "bind": "$.totalBalance",
                  "format": "number"
                }
              ]
            },
            {
              "id": "orderText",
              "type": "staticText",
              "text": "'You clear them in this order: ' & payoffOrder"
            },
            {
              "id": "sep2",
              "type": "separatorLine"
            },
            {
              "id": "balanceChart",
              "type": "dataChart",
              "label": "What you still owe, month by month",
              "chartType": "line",
              "bind": "$.schedule",
              "chartX": "month",
              "chartSeries": [
                {
                  "field": "balance",
                  "label": "Balance remaining"
                }
              ]
            },
            {
              "id": "scheduleTable",
              "type": "dataTable",
              "label": "Month by month",
              "bind": "$.schedule",
              "tableColumns": [
                {
                  "field": "month",
                  "header": "Month",
                  "width": "25%"
                },
                {
                  "field": "balance",
                  "header": "Balance left",
                  "format": "number",
                  "width": "40%"
                },
                {
                  "field": "interest",
                  "header": "Interest charged",
                  "format": "number",
                  "width": "35%"
                }
              ],
              "pageSize": 12
            }
          ]
        },
        {
          "id": "debtItem",
          "label": "Debt",
          "layout": "horizontal",
          "components": [
            {
              "id": "debtName",
              "type": "textField",
              "label": "Name",
              "bind": "$.debts[*].name",
              "placeholder": "Credit card"
            },
            {
              "id": "debtBalance",
              "type": "numericField",
              "label": "Balance",
              "bind": "$.debts[*].balance",
              "placeholder": "3000"
            },
            {
              "id": "debtApr",
              "type": "numericField",
              "label": "APR (%)",
              "bind": "$.debts[*].aprPct",
              "placeholder": "24"
            },
            {
              "id": "debtMin",
              "type": "numericField",
              "label": "Minimum payment",
              "bind": "$.debts[*].minPayment",
              "placeholder": "60"
            }
          ]
        }
      ]
    },
    "tests": [
      {
        "description": "three debts totalling 11,500 on a 600 budget, avalanche — highest rate first",
        "given": {
          "$.monthlyBudget": 600,
          "$.strategy": "avalanche"
        },
        "expect": {
          "$.totalBalance": 11500,
          "$.totalMinimums": 265,
          "$.monthsToFree": 23,
          "$.totalInterest": 1509.23,
          "$.clearsInHorizon": true,
          "$.interestSaved": 112.56,
          "$.schedule[0].interest": 142.5,
          "$.schedule[0].balance": 11042.5,
          "$.schedule[22].balance": 0
        }
      },
      {
        "description": "the same debts on snowball — clears in the same 23 months but costs 112.56 more in interest",
        "given": {
          "$.monthlyBudget": 600,
          "$.strategy": "snowball"
        },
        "expect": {
          "$.monthsToFree": 23,
          "$.totalInterest": 1621.79,
          "$.interestSaved": 112.56
        }
      },
      {
        "description": "paying only the minimums stretches it to 66 months and nearly quadruples the interest",
        "given": {
          "$.monthlyBudget": 265,
          "$.strategy": "avalanche"
        },
        "expect": {
          "$.monthsToFree": 66,
          "$.totalInterest": 5876.6,
          "$.interestSaved": 30.42,
          "$.clearsInHorizon": true
        }
      }
    ]
  }
}