{
  "slug": "cooling-degree-days",
  "title": "Cooling Degree Days Calculator",
  "heading": "Cooling Degree Days (CDD) Calculator",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/cooling-degree-days",
  "summary": "Estimate air conditioning demand and cost from average temperature above base 65°F.",
  "description": "Cooling degree days accumulate for each degree a day's average temperature exceeds a 65°F base — the mirror image of heating degree days. Utilities, HVAC engineers, and crop modelers use accumulated CDD to size air conditioning loads, forecast electric demand, and normalize summer energy bills across different weather years. A city with 1,800 annual CDD (like Chicago) has a moderate cooling season, while Phoenix runs over 4,000 CDD annually, which is why the same size house needs a much bigger AC system there. This calculator converts an average temperature and duration into CDD, then estimates kWh and cost using a simple building-load factor you calibrate from a past bill.",
  "formula": "CDD = max(0, avg daily temp − base) × days; estimated kWh = CDD × building factor ÷ SEER-derived efficiency term; cost = kWh × rate.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=cooling-degree-days",
  "inputs": [
    {
      "id": "avgTemp",
      "label": "Average outdoor temperature over period",
      "kind": "number",
      "hint": null,
      "default": 82,
      "unit": "°F",
      "min": 65,
      "max": 110
    },
    {
      "id": "days",
      "label": "Number of days",
      "kind": "number",
      "hint": null,
      "default": 30,
      "unit": null,
      "min": 1,
      "max": 365
    },
    {
      "id": "base",
      "label": "Base temperature",
      "kind": "number",
      "hint": null,
      "default": 65,
      "unit": "°F",
      "min": 60,
      "max": 70
    },
    {
      "id": "buildingFactor",
      "label": "kWh per CDD (from past bill)",
      "kind": "number",
      "hint": null,
      "default": 1.2,
      "unit": null,
      "min": 0.01,
      "max": null
    },
    {
      "id": "rate",
      "label": "Electricity rate per kWh",
      "kind": "number",
      "hint": null,
      "default": 0.16,
      "unit": "$",
      "min": 0,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "cdd",
      "label": "Total cooling degree days",
      "format": "number",
      "hint": null,
      "primary": true
    },
    {
      "id": "kwh",
      "label": "Estimated AC electricity",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "cost",
      "label": "Estimated cooling cost",
      "format": "currency",
      "hint": null,
      "primary": false
    },
    {
      "id": "perDay",
      "label": "Average CDD per day",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Average outdoor temperature over period: 82 °F",
      "Number of days: 30",
      "Base temperature: 65 °F",
      "kWh per CDD (from past bill): 1.2",
      "Electricity rate per kWh: 0.16 $"
    ],
    "outputs": [
      "Total cooling degree days: 510",
      "Estimated AC electricity: 612",
      "Estimated cooling cost: $97.92",
      "Average CDD per day: 17"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter average outdoor temperature over period (°F).",
      "Enter number of days.",
      "Enter base temperature (°F).",
      "Enter kwh per cdd (from past bill).",
      "Enter electricity rate per kwh ($).",
      "Read your total cooling degree days 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": {
        "avgTemp": 65,
        "days": 18,
        "base": 60,
        "buildingFactor": 0.72,
        "rate": 0.16
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "avgTemp": 82,
        "days": 30,
        "base": 65,
        "buildingFactor": 1.2,
        "rate": 0.16
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "avgTemp": 110,
        "days": 48,
        "base": 70,
        "buildingFactor": 1.92,
        "rate": 0.16
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "How does CDD relate to my AC's SEER rating?",
      "a": "Higher SEER means fewer kWh per CDD for the same building, so your building factor (kWh per CDD, back-calculated from an actual bill) already bakes in your specific system's efficiency, insulation, and house size without needing a separate SEER lookup."
    },
    {
      "q": "Why do some regions with lower peak temperatures have similar annual CDD to hotter ones?",
      "a": "CDD accumulates over the whole season, so a region with a long, mild summer (moderate heat for many months) can rack up similar total CDD to a region with a short, brutal summer — duration matters as much as peak intensity."
    },
    {
      "q": "Can I use this for a whole summer instead of a month?",
      "a": "Yes, just use the season's average daily temperature and total day count; NOAA publishes seasonal and annual CDD normals for most US cities if you want a benchmark instead of calculating from raw temperature logs."
    },
    {
      "q": "Does humidity affect the accuracy of CDD-based cost estimates?",
      "a": "Indirectly — CDD is temperature-only, but in humid climates AC systems run longer removing moisture at the same temperature, so the building factor calibrated from a humid-summer bill will already capture that extra load implicitly."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/heating-degree-days",
    "https://www.revenuelab.fyi/toolbox/heat-index-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Cooling Degree Days Calculator (https://www.revenuelab.fyi/toolbox/cooling-degree-days)"
}