{
  "slug": "kelly-criterion",
  "title": "Kelly Criterion Bet Size Calculator",
  "heading": "Kelly Criterion Calculator",
  "category": "math",
  "url": "https://www.revenuelab.fyi/toolbox/kelly-criterion",
  "summary": "Optimal stake as a fraction of bankroll for a given edge.",
  "description": "The Kelly formula sizes a position to maximize long-run growth. Enter your estimated win probability and the odds offered to see full Kelly, half Kelly, and the dollar stake.",
  "formula": "f* = (bp − q) ÷ b, where b = decimal odds − 1, p = win probability, q = 1 − p.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=kelly-criterion",
  "inputs": [
    {
      "id": "bankroll",
      "label": "Bankroll",
      "kind": "number",
      "hint": null,
      "default": 5000,
      "unit": "$",
      "min": 0,
      "max": null
    },
    {
      "id": "prob",
      "label": "Your win probability",
      "kind": "number",
      "hint": null,
      "default": 55,
      "unit": "%",
      "min": 0,
      "max": 100
    },
    {
      "id": "odds",
      "label": "Decimal odds offered",
      "kind": "number",
      "hint": null,
      "default": 2,
      "unit": null,
      "min": 1.01,
      "max": null
    },
    {
      "id": "fraction",
      "label": "Kelly fraction used",
      "kind": "number",
      "hint": null,
      "default": 50,
      "unit": "%",
      "min": 5,
      "max": 100
    }
  ],
  "outputs": [
    {
      "id": "stake",
      "label": "Recommended stake",
      "format": "currency",
      "hint": null,
      "primary": true
    },
    {
      "id": "kelly",
      "label": "Full Kelly fraction",
      "format": "percent",
      "hint": null,
      "primary": false
    },
    {
      "id": "usedPct",
      "label": "Fraction of bankroll used",
      "format": "percent",
      "hint": null,
      "primary": false
    },
    {
      "id": "ev",
      "label": "Expected value per unit",
      "format": "percent",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Bankroll: 5000 $",
      "Your win probability: 55 %",
      "Decimal odds offered: 2",
      "Kelly fraction used: 50 %"
    ],
    "outputs": [
      "Recommended stake: $250.00",
      "Full Kelly fraction: 10.00%",
      "Fraction of bankroll used: 5.00%",
      "Expected value per unit: 10.00%"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter bankroll ($).",
      "Enter your win probability (%).",
      "Enter decimal odds offered.",
      "Enter kelly fraction used (%).",
      "Read your recommended stake 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": {
        "bankroll": 3000,
        "prob": 33,
        "odds": 1.2,
        "fraction": 30
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "bankroll": 5000,
        "prob": 55,
        "odds": 2,
        "fraction": 50
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "bankroll": 8000,
        "prob": 88,
        "odds": 3.2,
        "fraction": 80
      }
    }
  ],
  "limitations": [
    "Results are rounded for display; the underlying calculation keeps full precision.",
    "Very large or very small inputs may hit floating-point limits in the browser.",
    "Inputs outside the accepted range are clamped rather than rejected."
  ],
  "faq": [
    {
      "q": "Why use half Kelly?",
      "a": "Full Kelly is brutally volatile and assumes your probability estimate is exact. Half Kelly keeps most of the growth with a fraction of the drawdown."
    },
    {
      "q": "What if the result is negative?",
      "a": "You have no edge at those odds. The correct stake is zero."
    }
  ],
  "related": [],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Kelly Criterion Bet Size Calculator (https://www.revenuelab.fyi/toolbox/kelly-criterion)"
}