{
  "slug": "marathon-finish-time",
  "title": "Marathon Finish Time Predictor",
  "heading": "Marathon Time Predictor",
  "category": "fitness-health",
  "url": "https://www.revenuelab.fyi/toolbox/marathon-finish-time",
  "summary": "Project a marathon or half finish time from a recent race result.",
  "description": "Riegel's formula projects longer-distance performance from a recent shorter race. Enter what you ran and how fast, and see the projected marathon, half, 10K, and 5K equivalents.",
  "formula": "T2 = T1 × (D2 ÷ D1)^1.06 (Riegel).",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=marathon-finish-time",
  "inputs": [
    {
      "id": "dist",
      "label": "Recent race distance",
      "kind": "number",
      "hint": null,
      "default": 6.2,
      "unit": "mi",
      "min": 0.5,
      "max": null
    },
    {
      "id": "mins",
      "label": "Finish time",
      "kind": "number",
      "hint": null,
      "default": 50,
      "unit": "min",
      "min": 1,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "marathon",
      "label": "Projected marathon",
      "format": "duration",
      "hint": null,
      "primary": true
    },
    {
      "id": "half",
      "label": "Projected half marathon",
      "format": "duration",
      "hint": null,
      "primary": false
    },
    {
      "id": "tenK",
      "label": "Projected 10K",
      "format": "duration",
      "hint": null,
      "primary": false
    },
    {
      "id": "fiveK",
      "label": "Projected 5K",
      "format": "duration",
      "hint": null,
      "primary": false
    },
    {
      "id": "marPace",
      "label": "Marathon pace (min/mi)",
      "format": "decimal",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Recent race distance: 6.2 mi",
      "Finish time: 50 min"
    ],
    "outputs": [
      "Projected marathon: 230",
      "Projected half marathon: 110",
      "Projected 10K: 50",
      "Projected 5K: 24",
      "Marathon pace (min/mi): 8.79"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter recent race distance (mi).",
      "Enter finish time (min).",
      "Read your projected marathon on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "dist": 3.7199999999999998,
        "mins": 30
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "dist": 6.2,
        "mins": 50
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "dist": 9.920000000000002,
        "mins": 80
      }
    }
  ],
  "limitations": [
    "Population formulas describe averages; individual bodies vary, especially at the extremes of height, age, or muscle mass.",
    "Results do not account for medical conditions, medication, or pregnancy.",
    "Use this as a directional reference, not a diagnosis — talk to a clinician before acting on it."
  ],
  "faq": [
    {
      "q": "How accurate is this?",
      "a": "Good within a few percent for trained runners projecting up to about double the input distance. It flatters undertrained runners projecting from a 5K to a marathon."
    },
    {
      "q": "Why 1.06?",
      "a": "It's the empirical fatigue exponent Pete Riegel derived from race data. Well-trained endurance athletes sometimes sit closer to 1.05."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/running-pace",
    "https://www.revenuelab.fyi/toolbox/calories-burned-running"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Marathon Finish Time Predictor (https://www.revenuelab.fyi/toolbox/marathon-finish-time)"
}