The contract sets the base temperature and how the daily average temperature is calculated. In an example in a report commissioned by the Japan Meteorological Agency, the daily average temperature is the day's maximum and minimum temperatures added together and divided by 2. The rules for futures on US cities that the US exchange CME (Chicago Mercantile Exchange) filed in May 2024 do the same, with a base of 65°F. Because those futures count in Fahrenheit, their values are in °F days. With a base of 18°C, a day with an average of 10°C has 8°C days of heating degree days, and a day with an average of 20°C has 2°C days of cooling degree days, and these are added up for each day of the period. A document from the Ministry of Land, Infrastructure, Transport and Tourism uses these terms and the unit °C days for indexes that estimate the heat needed for cooling and heating.
Degree day
- Japanese
- デグリーデー
- Also known as
- HDD, CDD
- Last reviewed
- September 25, 2026
This is a draft, shown for review before publication.
Degree days are the sum, over a set period, of the daily differences between the average temperature and a base temperature. Counted in Celsius, as temperatures are in Japan, the unit is °C days. Heating degree days (HDD) add up the differences on days when the average is below the base, and cooling degree days (CDD) add up the differences on days when it is above the base. They are used as indexes for weather derivatives.