Rex says
Everyday utility math — the kind you'd otherwise pull up four browser tabs for. I keep it to one clean answer.
Try a scenario
Click to load — tweak from there.Inputs
Result
Total cooling degree days
510
Estimated AC electricity
612
Estimated cooling cost
$97.92
Average CDD per day
17.0
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How to use this
- 1Enter average outdoor temperature over period (°F).
- 2Enter number of days.
- 3Enter base temperature (°F).
- 4Enter kwh per cdd (from past bill).
- 5Enter electricity rate per kwh ($).
- 6Read your total cooling degree days on the right — it updates as you type.
- 7Hit Share to keep the scenario or send it to someone.
About this calculator
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.
Worked example
Using the values the calculator loads with:
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 $
Results
- Total cooling degree days: 510
- Estimated AC electricity: 612
- Estimated cooling cost: $97.92
- Average CDD per day: 17
What each field means
Inputs
- Average outdoor temperature over period (°F)
- The average outdoor temperature over period used in the calculation, measured in °F. Starts at 82 °F so you have a working example on load. Accepted range: 65–110 °F.
- Number of days
- The number of days used in the calculation. Starts at 30 so you have a working example on load. Accepted range: 1–365.
- Base temperature (°F)
- The base temperature used in the calculation, measured in °F. Starts at 65 °F so you have a working example on load. Accepted range: 60–70 °F.
- kWh per CDD (from past bill)
- The kwh per cdd (from past bill) used in the calculation. Starts at 1.2 so you have a working example on load.
- Electricity rate per kWh ($)
- The electricity rate per kwh used in the calculation, measured in $. Starts at 0.16 $ so you have a working example on load.
Results
- Total cooling degree days
- Returned as a whole number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated AC electricity
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Estimated cooling cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Average CDD per day
- Returned as a whole number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does CDD relate to my AC's SEER rating?
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.
Why do some regions with lower peak temperatures have similar annual CDD to hotter ones?
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.
Can I use this for a whole summer instead of a month?
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.
Does humidity affect the accuracy of CDD-based cost estimates?
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.
Accuracy and 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.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Cooling Degree Days Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cooling-degree-days
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cooling-degree-days" target="_blank" rel="noopener">Cooling Degree Days Calculator — RevenueLab</a> (2026).</p>
Source: [Cooling Degree Days Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cooling-degree-days) (2026).